Abstract: Thermal electron attachment to SF(5)Cl has been studied with the flowing afterglow Langmuir probe technique. The rate coefficient is moderate, 4.8(+/-1.2)x10(-8) cm(3) s(-1), and invariant with temperature over the temperature range of 300-550 K. The reaction is dissociative, forming mainly SF(5) (-)+Cl. Minor yields of Cl(-) and FCl(-) were also found. The yields of the minor channels increase slightly with temperature. Statistical unimolecular rate modeling is employed to elucidate the character of the dissociation pathways and to support the assumption that the dissociations involve the formation of metastable anionic SF(5)Cl(-).

Abstract: AIMS: To use selected ion flow tube mass spectrometry (SIFT-MS) to analyse the molecular species emitted by heated 'street' cannabis plant material, especially targeting ammonia. MATERIALS AND METHODS: Samples of 'street' cannabis leaf, held under a UK Home Office licence, were prepared by finely chopping and mixing the material. The samples were then heated in commercially available devices. The air containing the released gaseous compounds was sampled into the SIFT-MS instrument for analysis. Smoke from standard 3% National Institute on Drug Abuse (NIDA) cannabis cigarettes was also analysed. FINDINGS: For 'street' cannabis, ammonia was present in the air samples from the devices at levels approaching 200 parts per million (p.p.m.). This is compared with peak levels of 10 p.p.m. using NIDA samples of known provenance and tetrahydrocannabinol content (3%). Several other compounds were present at lower levels, including acetaldehyde, methanol, acetone, acetic acid and uncharacterized terpenes. CONCLUSIONS: Awareness of the risks of inhaling the smoke directly from burning cannabis has led to the development of a number of alternative methods of delivery, which are claimed to be safer than direct smoking. Ammonia at toxic levels is produced from heating 'street' cannabis in these commercially available devices. Thus, the use of these devices to deliver 'street' cannabis is now open to question and further research is needed to investigate their safety.

Abstract: A study has been carried out, involving three healthy volunteers, of the ammonia levels in breath exhaled via the mouth and via the nose and in the static oral cavity using on-line, selected ion flow tube mass spectrometry (SIFT-MS), obviating the problems associated with sample collection of ammonia. The unequivocal conclusion drawn is that the ammonia appearing in the mouth-exhaled breath of the three volunteers is largely generated in the oral cavity and that the ammonia originating at the alveolar interface in the lungs is typically at levels less than about 100 parts-per-billion, which is a small fraction of the total breath ammonia. This leads to the recommendation that exhaled breath analyses should focus on nose-exhaled breath if the objective is to use breath analysis to investigate systemic, metabolic disease. Copyright (C) 2008 John Wiley & Sons, Ltd.

Abstract: A study has been carried out of the reactions of three isomers of hydroxybutyric acid, giving special attention to 3-hydroxybutyric acid, 3-HBA, with H3O+ and NO+ ions to acquire the required kinetic data for a selected ion flow tube mass spectrometry, SIFT-MS, search for 3-HBA in the headspace of urine since it is known to be one of the �ketone bodies� important in the diagnosis of ketoacidosis. Thus, the product ions formed in the reactions of the H3O+ and NO+ precursor ions with the three hydroxy acids were established by sampling the headspace above the pure compounds over a range of absolute humidities from 1.5% (ambient air) to 6% (liquid headspace at 37 C and exhaled breath). Then these data, together with the rate coefficients for the reactions estimated by calculation, were used to detect and quantify 3-HBA in the headspace of an aqueous solution of this compound of known concentration and above urine donated by two volunteers. The level of 3-HBA above the urine samples after they were acidified with hydrochloric acid was seen to be typically 40 parts-per-billion, ppb, which is much lower than that for acetone seen to be typically 800ppb. Exploiting the aqueous solution data as a reference, the 3-HBA concentration in the urine samples was estimated to be about 1-2 mmol/L, which is typical of the urine from healthy individuals. (c) 2008 Elsevier B.V. All rights reserved.

Abstract: Selected ion flow tube mass spectrometry (SIFT-MS) has been used to carry out a pilot parallel study on five volunteers to determine changes occurring in several trace compounds present in exhaled breath and emitted from skin into a collection bag surrounding part of the arm, before and after ingesting 75 g of glucose in the fasting state. SIFT-MS enabled real-time quantification of ammonia, methanol, ethanol, propanol, formaldehyde, acetaldehyde, isoprene and acetone. Following glucose ingestion, blood glucose and trace compound levels were measured every 30 min for 2 h. All the above compounds, except formaldehyde, were detected at the expected levels in exhaled breath of all volunteers; all the above compounds, except isoprene, were detected in the collection bag. Ammonia, methanol and ethanol were present at lower levels in the bag than in the breath. The aldehydes were present at higher levels in the bag than in breath. The blood glucose increased to a peak about 1 h post-ingestion, but this change was not obviously correlated with temporal changes in any of the compounds in breath or emitted by skin, except for acetone. The decrease in breath acetone was closely mirrored by skin-emitted acetone in three volunteers. Breath and skin acetone also clearly change with blood glucose and further work may ultimately enable inferences to be drawn of the blood glucose concentration from skin or breath measurements in type 1 diabetes. Copyright (C) 2008 John Wiley & Sons, Ltd.

Abstract: Collection of exhaled breath condensate (EBC) is a relatively simple noninvasive method of breath analysis; however, no data have been reported that would relate concentration of volatile compounds in EBC to their gaseous concentrations in exhaled air. The aim of the study was to investigate which volatile compounds are present in EBC and how their concentrations relate to results of direct breath analysis. Thus, samples of EBC were collected in a standard way from several subjects and absolute levels of several common volatile breath metabolites (ammonia, acetone, ethanol, methanol, propanol, isoprene, hydrogen cyanide, formaldehyde and acetaldehyde) were then determined in their headspace using selected ion flow tube mass spectrometry (SIFT-MS). Results are compared with those from on-line breath analyses carried out immediately before collecting the EBC samples. It has been demonstrated that SIFT-MS can be used to quantify the concentrations of volatiles in EBC samples and that, for methanol, ammonia, ethanol and acetone, the EBC concentrations correlate with the direct breath levels. However, the EBC concentrations of isoprene, formaldehyde, acetaldehyde, hydrogen cyanide and propanol do not correlate with direct breath measurements.

Abstract: Selected ion flow tube mass spectrometry (SIFT-MS) has been used to carry out a pilot parallel study on five volunteers to determine changes occurring in several trace compounds present in exhaled breath and emitted from skin into a collection bag surrounding part of the arm, before and after ingesting 75 g of glucose in the fasting state. SIFT-MS enabled real-time quantification of ammonia, methanol, ethanol, propanol, formaldehyde, acetaldehyde, isoprene and acetone. Following glucose ingestion, blood glucose and trace compound levels were measured every 30 min for 2 h. All the above compounds, except formaldehyde, were detected at the expected levels in exhaled breath of all volunteers; all the above compounds, except isoprene, were detected in the collection bag. Ammonia, methanol and ethanol were present at lower levels in the bag than in the breath. The aldehydes were present at higher levels in the bag than in breath. The blood glucose increased to a peak about 1 h post-ingestion, but this change was not obviously correlated with temporal changes in any of the compounds in breath or emitted by skin, except for acetone. The decrease in breath acetone was closely mirrored by skin-emitted acetone in three volunteers. Breath and skin acetone also clearly change with blood glucose and further work may ultimately enable inferences to be drawn of the blood glucose concentration from skin or breath measurements in type 1 diabetes.

Abstract: A study has been carried out, involving three healthy volunteers, of the ammonia levels in breath exhaled via the mouth and via the nose and in the static oral cavity using on-line, selected ion flow tube mass spectrometry (SIFT-MS), obviating the problems associated with sample collection of ammonia. The unequivocal conclusion drawn is that the ammonia appearing in the mouth-exhaled breath of the three volunteers is largely generated in the oral cavity and that the ammonia originating at the alveolar interface in the lungs is typically at levels less than about 100 parts-per-billion, which is a small fraction of the total breath ammonia. This leads to the recommendation that exhaled breath analyses should focus on nose-exhaled breath if the objective is to use breath analysis to investigate systemic, metabolic disease.

Abstract: BACKGROUND: Despite its importance, total body water (TBW) is usually estimated rather than measured due to the complexity of isotope dilution methods. The aim of this study was to demonstrate the applicability in haemodialysis (HD) patients of a recently developed on-line breath test, previously validated in healthy subjects, that uses the gold standard deuterium dilution method to measure TBW. In particular we wished to show that a pre-dialysis estimation was as good as a post-dialysis equilibrated measurement in order to avoid patients needing to remain behind after dialysis treatment. METHODS: The dispersal kinetics of breath HDO, measured using a flowing afterglow mass spectrometer (FA-MS) following ingestion of D(2)O immediately post-dialysis, were determined in 12 haemodialysis patients and used to calculate the absolute TBW(PostHD) after full equilibration. TBW(PreHD) was then determined from breath samples taken immediately prior to the next dialysis. This measurement was adjusted for the interdialytic weight change and urine output (TBW(PreHD-adjusted)) and compared to the TBW(PostHD). The accuracy and precision of FA-MS was also assessed using known concentrations of deuterium-enriched water samples. RESULTS: Mean TBW(PostHD) was 50.0 +/- 9.3 L and TBW(PreHD-adjusted) was 50.7 +/- 9.0 L. They were highly correlated (R = 0.99, P < 0.001) with a CV of 2.6%. The mean difference was +0.74 L (SEM 0.35, 95% CI -0.03 to 1.51 L, P = 0.059), compatible with a daily insensible loss of 0.37 L. Accuracy and precision of FA-MS were comparable to the previous validation work. CONCLUSIONS: This non-invasive adaptation of the D isotope dilution method for determining TBW can be applied to haemodialysis patients who show deuterium equilibration kinetics identical to normal subjects; a pre-dialysis estimation may be used to determine TBW, and so avoiding the necessity to remain behind after dialysis making this suitable for application in the clinical setting.

Abstract: The potential of breath analysis for clinical diagnosis and the strengths and weaknesses of the analytical methods used are discussed. Special attention is given to selected ion flow tube mass spectrometry, SIFT-MS, using which on-line real-time analyses of single breath exhalations can be carried out. Illustrative data on the concentration distributions of several breath metabolites amongst the healthy population are presented and their relations to disease when elevated above the normal are alluded to.

Abstract: Selected ion flow tube mass spectrometry, (SIFT-MS), is a technique for simultaneous real-time quantification of several trace gases in air and exhaled breath. It relies on chemical ionization of the trace gas molecules in air/breath samples introduced into helium carrier gas, using H3O+, NO+ and O-2(+) reagent (precursor ions). Reactions between the precursor ions and the trace gas molecules proceed for an accurately defined time, the precursor and product ions being detected and counted by a downstream mass spectrometer. Absolute concentrations of trace gases in single breath exhalation can be determined by SIFT-MS down to parts-per-billion (ppb) levels, obviating sample collection into bags or onto traps. Calibration using chemical standards is not required, as the concentrations are calculated using the known reaction rate constants and measured flow rates and pressures. SIFT-MS has been used for many pilot investigations in several areas of research, especially as a non-invasive breath analysis tool to investigate physiological processes in humans and animals, for clinical diagnosis and for therapeutic monitoring. Examples of the results obtained from several such studies are outlined to demonstrate the potential of SIFT-MS for trace gas analysis of air, exhaled breath and the headspace above liquids.

Abstract: The performance of the ion sources used in selected ion flow tube mass spectrometry, SIFT-MS, instruments is paramount in determining their sensitivities and detection limits for trace gas analysis. The microwave discharge plasma ion source that is currently used for the production of currents of the precursor H3O+, NO+ and O-2(+) ions for SIFT-MS is described, and the ion chemistry occurring within the plasma and the dissociation of the precursor ions on the helium carrier gas are considered. Thus, it is shown that the most suitable ion source gas composition is a mixture comprising maximal water vapour and minimal air at the lowest total pressure at which the discharge is sustained and stable. It is also shown that the injection energies of the precursor ions into the helium carrier gas must be kept low to minimize collisional dissociation of the ions and thus to minimize the fraction of reactive impurity ions in the carrier gas. Under these conditions, count rates greater than 10(6)s(-1) of all three precursor ion species with less than 1% of impurity ions have been achieved, which has moved the detection limit of SIFT-MS analyses of the volatile metabolites present in exhaled breath and ambient air into the 0.1-1 parts-per-billion concentration regime. (C) 2007 Elsevier B.V. All rights reserved.

Abstract: The potential of breath analysis for clinical diagnosis and the strengths and weaknesses of the analytical methods used are discussed. Special attention is given to selected ion flow tube mass spectrometry, SIFT-MS, using which on-line real-time analyses of single breath exhalations can be carried out. Illustrative data on the concentration distributions of several breath metabolites amongst the healthy population are presented and their relations to disease when elevated above the normal are alluded to.

Abstract: Exhaled breath analysis for clinical diagnosis and therapeutic monitoring is described with special reference to the techniques used and the underlying chemistry and physics involved. Brief outlines are given of the research carried out to date, and prospects for the future of this potentially valuable non-invasive technique are indicated.

Abstract:

Abstract: Selected ion flow tube mass spectrometry, (SIFT-MS), is a technique for simultaneous real-time quantification of several trace gases in air and exhaled breath. It relies on chemical ionization of the trace gas molecules in air/breath samples introduced into helium carrier gas, using H(3)O(+), NO(+) and O(2)(+) reagent (precursor ions). Reactions between the precursor ions and the trace gas molecules proceed for an accurately defined time, the precursor and product ions being detected and counted by a downstream mass spectrometer. Absolute concentrations of trace gases in single breath exhalation can be determined by SIFT-MS down to parts-per-billion (ppb) levels, obviating sample collection into bags or onto traps. Calibration using chemical standards is not required, as the concentrations are calculated using the known reaction rate constants and measured flow rates and pressures. SIFT-MS has been used for many pilot investigations in several areas of research, especially as a non-invasive breath analysis tool to investigate physiological processes in humans and animals, for clinical diagnosis and for therapeutic monitoring. Examples of the results obtained from several such studies are outlined to demonstrate the potential of SIFT-MS for trace gas analysis of air, exhaled breath and the headspace above liquids.

Abstract:

Abstract: A complete description is presented of a numerical method that allows the calculation, in real time, of absolute concentrations of trace gases, including volatile organic compounds and water vapour, from selected ion flow tube mass spectrometry, SIFT-MS, data. No assumptions are made concerning the SIFT-MS instrument size or its configuration and thus the calculation can be applied to the currently available, relatively large instruments and the anticipated new generation of smaller SIFT-MS instruments. This numerical method clearly distinguishes those parameters that are obviously specific to a particular instrument, including flow tube geometry, degree of mass discrimination in the analytical mass spectrometer and flow tube reaction time, from general fundamental processes, in particular the differential diffusive loss of ions along the flow tube that is dependent on the properties of those ions involved in the determination of the concentrations of particular trace gases. The essential reaction and transport kinetics are outlined, which describe the formation and loss of the product ions formed in the chemical ionisation of the trace gases by the precursor ions. A generalised calculation of the required ionic diffusion coefficients is introduced with options either for their accurate determination from the molecular geometry of ions or for less accurate but simpler estimates obtained using just the ionic mass. Based on the above ideas, a straightforward calculation sequence is shown to determine trace gas concentrations by SIFT-MS, and its utility demonstrated by an example of the analysis of acetone in exhaled breath. (c) 2005 Elsevier B.V. All rights reserved.

Abstract: Selected-ion flow-tube mass spectrometry (SIFT-MS) has been used to monitor the volatile compounds in the exhaled breath of 30 volunteers (19 male, 11 female) over a 6-month period. Volunteers provided breath samples each week between 8:45 and 13:00 (before lunch), and the concentrations of several trace compounds were obtained. In this paper the focus is on ethanol and acetaldehyde, which were simultaneously quantified by SIFT-MS using H3O+ precursor ions. The mean ethanol level for all samples was 196 parts-per-billion (ppb) with a standard deviation of 244 ppb, and the range of values for breath samples analysed is 0 to 1663 ppb. The mean acetaldehyde level for all samples was 24 ppb with a standard deviation of 17 ppb, and the range of values for breath samples analysed is 0 to 104 ppb. Background (ambient air) levels of ethanol were around 50 ppb, whereas any background acetaldehyde was usually undetectable. Increased ethanol levels were observed if sweet drink/food had been consumed within the 2 h prior to providing the breath samples, but no increase was apparent when alcohol had been consumed the previous evening. The measured endogenous breath ethanol and acetaldehyde levels were not correlated. These data relating to healthy individuals are a prelude to using breath analysis for clinical diagnosis, for example, the recognition of bacterial overload in the gut (ethanol) or the possibly of detecting tumours in the body (acetaldehyde).

Abstract: The ingestion of relatively large doses of the vitamin niacin by healthy volunteers results in a reddening of the skin, a skin 'flush'. Thus, we have carried out a study of the breath metabolites of two healthy volunteers following (i) the ingestion of 200 mg of immediate-release niacin, (ii) as (i) but preceded by the ingestion of 325 mg of aspirin that diminishes the skin 'flush', (iii) ingestion of 500 mg of slow-release niacin. On-line breath analysis was carried out using selected ion flow tube mass spectrometry, SIFT-MS. The interesting new observation is that the breath ammonia levels of both volunteers clearly increased following (i) and (ii), and an obvious skin flush did occur following (i) but not following (ii). The slow-release niacin (iii) did not result in a flush and the breath ammonia levels increased more slowly and did not reach the higher levels produced by (i) and (ii). The results of these experiments demonstrate that breath ammonia levels are dependent on the blood/plasma levels of niacin, but are not directly related to the flushing phenomenon, and that the observed increases in blood/breath ammonia levels are consistent with current knowledge of the metabolic pathways of niacin. The parallel measurements of breath isoprene are presented, which demonstrate the quality of breath analyses that can be achieved using SIFT-MS.

Abstract: Selected ion flow tube mass spectrometry, SIFT-MS, has been used to monitor the volatile compounds in the exhaled breath of 30 volunteers (19 males, 11 females) over a 6 month period. Volunteers provided breath samples each week between 8:45 am and 1 pm (before lunch), and the concentrations of several trace compounds were obtained. In this paper the focus is on ammonia, acetone and propanol. It was found that the concentration distributions of these compounds in breath were close to log-normal. The median ammonia level estimated as a geometric mean for all samples was 833 parts per billion (ppb) with a multiplicative standard deviation of 1.62, the values ranging from 248 to 2935 ppb. Breath ammonia clearly increased with increasing age in this volunteer cohort. The geometric mean acetone level for all samples was 477 parts per billion (ppb) with a multiplicative standard deviation of 1.58, the values ranging from 148 to 2744 ppb. The median propanol level for all samples was 18 ppb, the values ranging from 0 to 135 ppb. A weak but significant correlation between breath propanol and acetone levels is apparent in the data. The findings indicate the potential value of SIFT-MS as a non-invasive breath analysis technique for investigating volatile compounds in human health and in the diseased state.

Abstract: Selected ion flow tube mass spectrometry, SIFT-MS, has been used to monitor the volatile compounds in the exhaled breath of 30 volunteers (19 male, 11 female) over a six-month period. Volunteers provided breath samples each week between 8:45 am and 1 pm (before lunch), and the concentrations of several trace compounds were obtained. In this paper the focus is on methanol in breath. The median methanol level determined using the H(3)O(+) precursor ions for all samples was 461 parts-per-billion (ppb), the concentrations for all the samples ranging from 32 to 1684 ppb. The distribution of breath methanol concentration is seen to be log-normal for this healthy population; the geometric mean was 450 ppb, close to the median value, and the multiplicative (geometric) standard deviation was 1.62. Breath methanol is not correlated with age, breath ethanol or ethanol consumed in the previous 24 h, but there was an inverse correlation with body mass index (BMI) for the cohort of volunteers recruited for this study. Observed breath methanol levels are well compatible with the previously published blood methanol levels. Some tentative suggestions are made concerning the origin of endogenous methanol.

Abstract: Selected ion flow tube mass spectrometry (SIFT-MS) has been used to measure simultaneously the concentrations of both carbon disulphide and acetone in exhaled breath following the ingestion of a single dose of disulfiram (Antabuse). Carbon disulphide is a product of the metabolism of disulfiram and is excreted mainly through the lungs. Acetone is a product of normal metabolism and appears in the breath of all individuals. These breath analyses were performed in single exhalations and the results were available in real time. The levels of breath acetone and carbon disulphide were compared with levels obtained from a control subject who had not ingested disulfiram. Breath carbon disulphide was seen to increase from 15 p.p.b. to 618 p.p.b. over a 28-hour period, in the single individual tested, following ingestion of disulfiram, while acetone levels increased from 300 p.p.b. (normal) to over 4000 p.p.b. (greatly elevated). No such increases were seen in the breath of the control subject over the same period. An obvious positive correlation between breath carbon disulphide and acetone concentrations following disulfiram ingestion is seen and discussed.

Abstract: BACKGROUND: Selected ion flow tube mass spectrometry allows trace gas quantification in exhaled breath and in the air/vapor above liquids (headspace) down to the 10 parts-per-billion level. During selected ion flow tube mass spectrometry investigation of the volatile compounds emitted by urine, high acetone levels were incidentally identified in the headspace of urine from healthy female volunteers around their mid-cycle. Hence, this study was designed to measure urine headspace acetone levels throughout the menstrual cycle. METHODS: Using selected ion flow tube mass spectrometry we measured daily urine headspace acetone concentrations of seven ovulating (group 1) and three postmenopausal volunteers (group 2). RESULTS: A several-fold increase in urine headspace acetone level was detected 2-3 days after the predicted day of ovulation in 5 of the 7 volunteers in group 1. No such rise was detected in group 2. CONCLUSION: This study provides the basis for future research to understand the reason for and the potential utility of this phenomenon.

Abstract: The value of the gas chromatography (GC) and selected ion flow tube mass spectrometry (SIFT-MS) combination for the analysis of trace gases is demonstrated by the quantification of acetone in air samples using the three precursor ions available to SIFT-MS, viz. H3O+, NO+ and O2+, and by the separation of the isomers 1-propanol and 2-propanol, and their analysis using H3O+ precursor ions. It is shown that the GC/SIFT-MS combination allows for accurate trace gas quantification obviating the regular, time-consuming calibrations that are usually required for the more commonly used detectors of GC systems, and the positive identification of isomers in mixtures that is often challenging using SIFT-MS alone. Thus, the GC/SIFT-MS combination paves the way to more confident analyses of complex mixtures such as exhaled breath.

Abstract: The increase in ammonia and ethanol in the exhaled breath stream following mouthwashes by aqueous solutions of urea and sugar (sucrose), respectively, has been investigated by analysing exhaled breath in real time using selected ion flow tube mass spectrometry, SIFT-MS. It is shown that the measured levels of these compounds in the stream of exhaled breath can be much greater than the endogenous levels originating at the alveolar boundary. Thus, it is concluded that without careful preparation, mouth production of these compounds, and other compounds as yet unidentified, can seriously compromise the quantification of truly endogenous trace compounds present in blood and in the alveolar breath, as required for clinical diagnosis, and can probably introduce additional compounds into the breath stream that could seriously mislead breath analysis. The concentrations of both the urea and sucrose solutions used to enhance the ammonia and ethanol levels were larger than normally present in food and drinks and so in most situations such severe enhancements will not occur.

Abstract: Samples (210 in total) of broncholaveolar lavages (BALs), obtained from patients hospitalized with pneumonia in various departments of two hospitals, were analysed using the method of solid phase microextraction-gas chromatography (SPME-GC) with FID detection. Up to 20% (9% unequivocally, 11% probably) of these samples was found to contain volatile fatty acids (VFAs) in the series from acetic acid to heptanoic acid. Importantly, the presence of these acids indicates the presence of fermenting anaerobic bacteria, which were not detected by the conventional microbiological examination. Other compounds, namely the heptanol and cyclohexanone, were also detected by this method in some samples. Cyclohexanone occurred almost exclusively in samples from patients receiving intensive care with mechanical ventilation, and is suspected to originate from plastic parts of ventilators. Selected representative samples were also analysed using further methods, namely gas chromatography-mass spectrometry (GC-MS) of native and silylated samples, and selected ion flow tube mass spectrometry (SIFT-MS). These methods confirmed the identities of above mentioned compounds, and detected numerous other compounds tentatively identified as various alcohols, aldehydes, ketones, esters and hydrogen cyanide, HCN. Most of these compounds occurred in small amounts and their origin and diagnostic significance remains uncertain, except, that is, for the HCN, which indicates the presence of Pseudomonas aeruginosa.

Abstract: Thirty volunteers (19 males, 11 females) were recruited for a 6-month study of the volatile compounds in their exhaled breath using the selected ion flow tube mass spectrometry (SIFT-MS) analytical technique. Volunteers provided weekly breath samples between 8:45 am and 1 pm (before lunch), and the concentrations of several trace compounds were obtained. In this paper, we focus on the isoprene in alveolar breath, which was monitored by SIFT-MS using NO(+) precursor ions. The mean isoprene level for all samples was 118 parts per billion (ppb) with a standard deviation of 68 ppb and the range of values for breath samples given is 0-474 ppb. Variability in isoprene levels was similar in most volunteers. Isoprene levels increased immediately after moderate exercise, but returned to normal within 2-3 min for those few volunteers that were investigated. Cholesterol levels analysed for only three of the subjects were not obviously correlated with isoprene concentration in breath. Differences in isoprene levels were not directly correlated to gender, age or body mass index.

Abstract: Pseudomonas aeruginosa (PA) is associated with a distinctive smell produced by a combination of volatile compounds (VCs). Selected ion flow tube mass spectrometry (SIFT-MS) provides a novel and rapid methodology for rapid, accurate detection of trace quantities (parts per billion; ppb) of VCs in air. We studied the VCs produced by different isolates of PA cultures in vitro from patients with cystic fibrosis. Twenty-one patients with cystic fibrosis provided sputum and cough swab samples for culture. These were used to inoculate blood agar (BA) and Pseudomonas-selective media (PSM). These plates were incubated for 48 hr at 37 degrees C inside sealed plastic bags. The air surrounding the samples after 48 hr (headspace) was analyzed using SIFT-MS. PA growth was commonly associated with the production of significant quantities of VCs, notably hydrogen cyanide gas (HCN). This was detectable in the headspace of 15/22 of PA-positive samples. In contrast, it was only seen in the headspace of 1/13 control samples (6 sterile plates and 7 plates with only mixed upper respiratory tract flora). The concentration of HCN was significantly higher above PA-positive samples than above other bacterial growth (P < 0.01), and in our study, levels of HCN greater than 100 ppb were a sensitive (68%) and highly specific (100%) biomarker of PA. SIFT-MS can detect a range of VCs from PA in vitro. HCN may be a specific indicator of PA infection in vivo, and offers promise as a biomarker for noninvasive detection of PA infection by breath analysis. (c) 2005 Wiley-Liss, Inc.

Abstract: Selected ion flow tube mass spectrometry (SIFT-MS) is a new analytical technique for the real-time quantification of several trace gases simultaneously in air and breath. It relies on chemical ionization of the trace gas molecules in air/breath samples introduced into helium carrier gas using H3O+, NO+, and O-2(+center dot) precursor ions. Reactions between the precursor ions and trace gas molecules proceed for an accurately defined time, the precursor and product ions being detected and counted by a downstream mass spectrometer, thus effecting quantification. Absolute concentrations of trace gases in single breath exhalation can be determined by SIFT-MS down to ppb levels, obviating sample collection and calibration. Illustrative examples of SIFT MS studies include (i) analysis of gases from combustion engines, animals and their waste, and food; (ii) breath and urinary headspace studies of metabolites, ethanol metabolism, elevated acetone during ovulation, and exogenous compounds; and (iii) urinary infection and the presence of tumors, the influence of dialysis on breath ammonia, acetone, and isoprene, and acetaldehyde released by cancer cells in vitro. Flowing afterglow mass spectrometry (FA-MS) is briefly described, which allows on-line quantification of deuterium in breath water vapor. (c) 2004 Wiley Periodicals, Inc.

Abstract: A method to calculate diffusion coefficients of ions important for the selected ion flow tube mass spectrometry, SIFT-MS, is presented. The ions, on which this method is demonstrated, include the SIFT-MS precursors H3O+(H2O)(0,1.2,3), NO+(H2O)(0,1.2) and O-2(.+) and the product ions relevant to analysis of breath trace metabolites ammonia (NH3.+(H2O)(0,1,2,) NH4+(H2O)(0,1,2)), acetaldehyde (C2H4OH+(H2O)(0.1,2)), acetone (CH3CO+, (CH3)(2)CO.+, (CH3)(2)COH+(H2O)(0,1,) (CH3)(2)(CONO+)-N-.), ethanol (C2H5OHH+(H2O)(0,1,2)) and isoprene (C5H7+, C5H8.+, C5H9+). Theoretical model of the (12, 4) potential for interaction between the ions and the helium atoms is used, with the repulsive part approximated by the mean hard-sphere cross section and the attractive part describing ion-induced dipole interactions. The reduced zero-field mobilities at 300 K are calculated using the Viehland and Mason theory [L.A. Viehland, S.L. Lin, E.A. Mason, At. Data Nucl. Data Tables, 60 (1995) 37-95], parameterised by a simple formula as a function of the mean hard-sphere cross section, and converted to diffusion coefficients using the Einstein relation. The method is tested on a set of experimental data for simple ions and cluster ions. (c) 2005 Elsevier B.V. All rights reserved.

Abstract: Pseudomonas aeruginosa (PA) is associated with a distinctive smell produced by a combination of volatile compounds (VCs). Selected ion flow tube mass spectrometry (SIFT-MS) provides a novel and rapid methodology for rapid, accurate detection of trace quantities (parts per billion; ppb) of VCs in air. We studied the VCs produced by different isolates of PA cultures in vitro from patients with cystic fibrosis. Twenty-one patients with cystic fibrosis provided sputum and cough swab samples for culture. These were used to inoculate blood agar (BA) and Pseudomonas-selective media (PSM). These plates were incubated for 48 hr at 37 degrees C inside sealed plastic bags. The air surrounding the samples after 48 hr (headspace) was analyzed using SIFT-MS. PA growth was commonly associated with the production of significant quantities of VCs, notably hydrogen cyanide gas (HCN). This was detectable in the headspace of 15/22 of PA-positive samples. In contrast, it was only seen in the headspace of 1/13 control samples (6 sterile plates and 7 plates with only mixed upper respiratory tract flora). The concentration of HCN was significantly higher above PA-positive samples than above other bacterial growth (P < 0.01), and in our study, levels of HCN greater than 100 ppb were a sensitive (68%) and highly specific (100%) biomarker of PA. SIFT-MS can detect a range of VCs from PA in vitro. HCN may be a specific indicator of PA infection in vivo, and offers promise as a biomarker for noninvasive detection of PA infection by breath analysis.

Abstract: The three-pore model of peritoneal membrane physiology predicts sieving of small solutes as a result of the presence of a water-exclusive pathway. The purpose of this study was to measure the diffusive and convective components of small solute transport, including water, under differing convection. Triplicate studies were performed in eight stable individuals using 2-L exchanges of bicarbonate buffered 1.36 or 3.86% glucose and icodextrin. Diffusion of water was estimated by establishing an artificial gradient of deuterated water (HDO) between blood/body water and the dialysate. (125)RISA (radio-iodinated serum albumin) was used as an intraperitoneal volume marker to determine the net ultrafiltration and reabsorption of fluid. The mass transfer area coefficient (MTAC) for HDO and solutes was estimated using the Garred and Waniewski equations. The MTAC of HDO calculated for 1.36% glucose and icodextrin were similar (36.8 versus 39.7 ml/min; P = 0.3), whereas for other solutes, values obtained using icodextrin were consistently higher (P < 0.05). A significant increase in the MTAC of HDO was demonstrated with an increase in the convective flow of water when using 3.86% glucose (mean value, 49.5 ml/min; P < 0.05). MTAC for urea was also increased with 3.86% glucose. The identical MTAC for water using 1.36% glucose and icodextrin indicates that diffusion is predominantly through small pores, whereas the difference in MTAC for the remaining solutes is a reflection of their sieving. The increase in the MTAC of water and urea associated with an increase in convection is most likely due to increased mixing within the interstitium.

Abstract: The three-pore model of peritoneal membrane physiology predicts sieving of small solutes as a result of the presence of a water-exclusive pathway. The purpose of this study was to measure the diffusive and convective components of small solute transport, including water, under differing convection. Triplicate studies were performed in eight stable individuals using 2-L exchanges of bicarbonate buffered 1.36 or 3.86% glucose and icodextrin. Diffusion of water was estimated by establishing an artificial gradient of deuterated water (HDO) between blood/body water and the dialysate. (125)RISA (radio-iodinated serum albumin) was used as an intraperitoneal volume marker to determine the net ultrafiltration and reabsorption of fluid. The mass transfer area coefficient (MTAC) for HDO and solutes was estimated using the Garred and Waniewski equations. The MTAC of HDO calculated for 1.36% glucose and icodextrin were similar (36.8 versus 39.7 ml/min; P = 0.3), whereas for other solutes, values obtained using icodextrin were consistently higher (P < 0.05). A significant increase in the MTAC of HDO was demonstrated with an increase in the convective flow of water when using 3.86% glucose (mean value, 49.5 ml/min; P < 0.05). MTAC for urea was also increased with 3.86% glucose. The identical MTAC for water using 1.36% glucose and icodextrin indicates that diffusion is predominantly through small pores, whereas the difference in MTAC for the remaining solutes is a reflection of their sieving. The increase in the MTAC of water and urea associated with an increase in convection is most likely due to increased mixing within the interstitium.

Abstract: Selected ion flow tube mass spectrometry (SIFT-MS) is a new analytical technique for the real-time quantification of several trace gases simultaneously in air and breath. It relies on chemical ionization of the trace gas molecules in air/breath samples introduced into helium carrier gas using H(3)O(+), NO(+), and O(2) (+.) precursor ions. Reactions between the precursor ions and trace gas molecules proceed for an accurately defined time, the precursor and product ions being detected and counted by a downstream mass spectrometer, thus effecting quantification. Absolute concentrations of trace gases in single breath exhalation can be determined by SIFT-MS down to ppb levels, obviating sample collection and calibration. Illustrative examples of SIFT-MS studies include (i) analysis of gases from combustion engines, animals and their waste, and food; (ii) breath and urinary headspace studies of metabolites, ethanol metabolism, elevated acetone during ovulation, and exogenous compounds; and (iii) urinary infection and the presence of tumors, the influence of dialysis on breath ammonia, acetone, and isoprene, and acetaldehyde released by cancer cells in vitro. Flowing afterglow mass spectrometry (FA-MS) is briefly described, which allows on-line quantification of deuterium in breath water vapor.

Abstract: A coordinated study of the dispersal of water between the various body compartments (stomach and gut, blood stream and tissue) and the similar dispersal kinetics of ethanol and its metabolism has been carried out involving two healthy volunteers using flowing afterglow mass spectrometry, FA-MS, and selected ion flow tube mass spectrometry, SIFT-MS. Thus, using these techniques, the variations of HDO and ethanol in breath, measured in successive single exhalations, were followed in real time after the ingestion of measured quantities of D2O and ethanol in proportion to the body weights of the subjects at the dose rates D2O similar to 0.283 g kg(-1), ethanol similar to 0.067 g kg(-1). During the FA-MS experimental periods (about 2 h), the dispersion of HDO into the body water and finally its equilibration in the total body water is observed from which total body water for each subject was determined. In the SIFT-MS measurements, the dispersion of ethanol into the body water and its loss via metabolism was observed until the physiological (pre-dose) breath level of ethanol for each individual was restored. A simple linear transformation is used to derive the time variations of the blood levels of HDO and ethanol. This has allowed a comparison of the fractions of the ingested ethanol that are metabolized during first-pass metabolism for the two subjects. Thus, in one subject 30% and in the other subject 40% of the ingested alcohol is metabolized in the first 20 min following ingestion. The good time resolution allowed by non-invasive breath analysis ensures that the rates of processes such as ethanol metabolism can be accurately measured. Simultaneous measurements of breath acetaldehyde (largely formed via the ethanol metabolism) and acetone were also performed during the SIFT-MS single breath exhalations.

Abstract: A coordinated study of the dispersal of water between the various body compartments (stomach and gut, blood stream and tissue) and the similar dispersal kinetics of ethanol and its metabolism has been carried out involving two healthy volunteers using flowing afterglow mass spectrometry, FA-MS, and selected ion flow tube mass spectrometry, SIFT-MS. Thus, using these techniques, the variations of HDO and ethanol in breath, measured in successive single exhalations, were followed in real time after the ingestion of measured quantities of D2O and ethanol in proportion to the body weights of the subjects at the dose rates D2O approximately 0.283 g kg-1, ethanol approximately 0.067 g kg-1. During the FA-MS experimental periods (about 2 h), the dispersion of HDO into the body water and finally its equilibration in the total body water is observed from which total body water for each subject was determined. In the SIFT-MS measurements, the dispersion of ethanol into the body water and its loss via metabolism was observed until the physiological (pre-dose) breath level of ethanol for each individual was restored. A simple linear transformation is used to derive the time variations of the blood levels of HDO and ethanol. This has allowed a comparison of the fractions of the ingested ethanol that are metabolized during first-pass metabolism for the two subjects. Thus, in one subject 30% and in the other subject 40% of the ingested alcohol is metabolized in the first 20 min following ingestion. The good time resolution allowed by non-invasive breath analysis ensures that the rates of processes such as ethanol metabolism can be accurately measured. Simultaneous measurements of breath acetaldehyde (largely formed via the ethanol metabolism) and acetone were also performed during the SIFT-MS single breath exhalations.

Abstract: With H3O+, NO+ and O-2(+) as the precursory ions, we have used selected ion flow tube mass spectrometry, SIFT-MS, to analyse the exhaust gas emitted by a car fitted with catalytic converter. The results show that the exhaust gas consists of a series of hydrocarbons ( including aliphatic alkanes, alkenes, alkynes, dienes and aromatic hydrocarbons), carbonyls (including aldehydes, ketones, alcohols), NOx and ammonia. For their kinetics processes of formation, we also gave some discussion in the paper. Among these compounds, the density of the NO is extremely high, and much more than the total density of others that our SIFT/MS can detect. Except for this, the concentration of the aromatic hydrocarbons and aldehydes are also very high. In addition, we also studied the difference between the cold start and warm start, and found that, for cold start condition, the hydrocarbons and NOx emissions are higher by a factor of 3similar to5 comparing to warm start condition, and carbonyls had no big change between two conditions, it also show that the catalytic converter is a effective way to diminish and control pollution of the exhaust gas from the car. In this paper, all compounds are detected simultaneously, which demonstrates the value of SIFT-MS in detecting the VOCs and NOx in the field of research.

Abstract: A simple ion source is described that consists of a glass discharge tube positioned judiciously in a rectangular waveguide resonator that is directly coupled to an under-run standard magnetron. This ion source operates well with gas mixtures, including rare gases, air and water vapour in the pressure range 10-100 Pa and at magnetron powers within the range 15-40 W. The main advantage of this magnetron/cavity arrangement is the absence of mechanically adjustable parts (aerial and tuning stub), in contrast to other commonly used arrangements that combine a cavity resonator that is connected to the magnetron via a launcher and a coaxial cable.

Abstract: Selected ion flow tube mass spectrometry (SIFT-MS) has been used to analyse on-line and in real time the exhaust gas emissions from a Caterpillar 3304 diesel engine under different conditions of load (idle and 50% of rated load) and speed (910, 1500 and 2200 rpm) using three types of fuel: an ultra-low-sulphur diesel, a rapeseed methyl ester and gas oil. SIFT-MS analyses of the alkanes, alkenes and aromatic hydrocarbons in the headspace of these fuels were also performed, but the headspace of the rapeseed methyl ester consists mainly of methanol and a compound with the molecular formula C4H8O. The exhaust gases were analysed for NO and NO2 using O-2(+). reagent ions and for HNO2 using H3O+ reagent ions. The following aldehydes and ketones in the exhaust gases were quantified by using the combination of H3O+ and NO+ reagent ions: formaldehyde, acetaldehyde, propenal, propanal, acetone, butanal, pentanal, butanone and pentanone. Formaldehyde, acetaldehyde and pentenal, all known respiratory irritants associated with sensitisation to asthma of workers exposed to diesel exhaust, are variously present within the range 100-2000 ppb. Hydrocarbons in the exhaust gases accessible to SIFT-MS analyses were also quantified as total concentrations of the various isomers Of C3H4, C3H6, C4H6, C5H8, C5H10, C6H8, C6H10, C7H14, C6H6, C7H8, C8H10 and C9H12. Copyright (C) 2004 John Wiley Sons, Ltd.

Abstract: Following our recent observation that Pseudomonas bacteria in vitro emit hydrogen cyanide, we have found it necessary to investigate the ion chemistry of this compound and to extend the kinetics database for selected ion flow tube mass spectrometry (SIFT-MS) to allow the accurate quantification of HCN in moist air samples, including exhaled breath. Because of the proximity of the proton affinities of HCN and H2O molecules, the presence of water vapour can significantly distort HCN analysis in the presence of water vapour and a more sophisticated analytical procedure has to be developed. Thus, the reactions of H3O+(H2O)(0,1,2,3) ions with HCN molecules have been studied in the presence of varying concentrations of water vapour, reactions on which SIFT-MS analysis of HCN relies. The results of these experiments have allowed an analytical procedure to be developed which has extended the kinetics database of SIFT-MS, such that HCN can now be quantified in humid air and in exhaled breath. Copyright (C) 2004 John Wiley Sons, Ltd.

Abstract: A selected ion flow tube. SIFT. study has been carried out of the reactions of H3O+, NO+ and O-2(+) with some volatile organic compounds that are released by bacteria. The major intention is to prepare the way for an extensive study of the emissions from Pseudomonas bacteria in vitro using selected ion flow tube mass spectrometry, SIFT-MS, with a view to detecting the presence of these bacteria in vivo. This requires an extensive SIFT-MS database of the rate coefficients and product ion distributions for the reactions of the above precursor ions with those molecular species that are released by or implicated in the growth of bacteria. A partial list of these molecular species is given. The available SIFT-MS database already includes the kinetic data for the reactions of several of these compounds and the present study supplements this to include 2-methyl-1-butanol and 2-heptanol, 3-methyl-1-butyl acetate, 4-methyl-1,3-pentadiene, and dimethyl trisulphide and dimethyl tetrasulphide. The kinetic data obtained in the present study are compared with those obtained previously for classes of similar compounds. (C) 2004 Elsevier B.V. All rights reserved.

Abstract: We present the results of a selected ion flow tube (SIFT) study of the reactions of H3O+, NO+ and O-2(.+) ions with 11 N-containing heterocyclic compounds and seven O-containing heterocyclic compounds, M. Most of these compounds have more than one functional group and some of them are known to occur in biological fluids and other media. The major objective is to provide the required kinetic data (rate coefficients and product ions) to extend the library for selected ion flow tube mass spectrometry, SIFT-MS, to allow these compounds to be detected and quantified in humid air samples. The results show that the H3O+ reactions are very simple, leading only to a stable protonated molecule. MH+, which facilitates SIFT-MS analyses. The NO+ reactions are also relatively simple, again mostly producing a single product ion species. which is variously M.+, (M-H)+ and NO+M, so NO+ is a suitable precursor ion species for the analysis of these compounds. Generally speaking. the O-2(.+) reactions result in more than one product ion following dissociative charge transfer and so O-2(.+) precursor ions are less suitable for SIFT-MS analyses of these heterocyclics. Some attention is given to the formation of the hydrates of the MH+ product ions via three-body association and/or switching reactions (in most cases only the monohydrate is produced), since these hydrates must be included in the SIFT-MS analyses of these heterocyclic compounds. (C) 2004 Elsevier B.V. All rights reserved.

Abstract: Following our recent observation that Pseudomonas bacteria in vitro emit hydrogen cyanide, we have found it necessary to investigate the ion chemistry of this compound and to extend the kinetics database for selected ion flow tube mass spectrometry (SIFT-MS) to allow the accurate quantification of HCN in moist air samples, including exhaled breath. Because of the proximity of the proton affinities of HCN and H2O molecules, the presence of water vapour can significantly distort HCN analysis in the presence of water vapour and a more sophisticated analytical procedure has to be developed. Thus, the reactions of H3O+(H2O)0,1,2,3 ions with HCN molecules have been studied in the presence of varying concentrations of water vapour, reactions on which SIFT-MS analysis of HCN relies. The results of these experiments have allowed an analytical procedure to be developed which has extended the kinetics database of SIFT-MS, such that HCN can now be quantified in humid air and in exhaled breath.

Abstract: We have carried out a selected ion flow tube (SIFT) study of the reactions of H3O+, NO+ and O-2(+.) with the following 10 compounds: 2-hydroxyphenol, 2-, 3- and 4-methylphenol (o-, m- and p-cresol, respectively), 4-ethylphenol, 1 -phenylmethanol (benzyl alcohol), 1- and 2-phenylethanol, 1,4-benzoquinone and cyclohexanone. The primary purpose of this work was to extend the kinetics database to allow these compounds (M), to be analysed in air by selected ion flow tube mass spectrometry (SIFT-MS). The initial step in all the H3O+ reactions is exotherraic proton transfer to produce MH+ ions, which are observed as the only products for seven of the ten reactions, but for the three aromatic alcohols, H2O molecule elimination occurred from the nascent MH+ ions producing the corresponding hydrocarbon ion. This is an essential point to recognise when exploiting proton transfer to analyse these compounds using SIFI-MS and proton transfer reaction mass spectrometry, PTR-MS. NO+ reacts with six of the compounds via non-dissociative charge transfer producing M+ ions and this is a valuable route to their analysis by SIFT-MS. In the case of the NO+/quinone reaction, adduct formation occurs giving NO+M product ions, whilst for the remaining three reactions two or more ion products were formed. All the O-2(+.) reactions proceeded via charge transfer with multiple ion products in most cases. A sample analysis is carried out to indicate the value of simultaneous use of both H3O+ and NO+ precursor ions to analyse a mixture containing some of these compounds. (C) 2004 Elsevier B.V. All rights reserved.

Abstract: We have carried out a selected ion flow tube (SIFT) study of the reactions of H3O+, NO+ and O-2(+.) with the following six nitroalkanes: nitromethane, nitroethane, 1-nitropropane, 2-nitropropane, 1-nitrobutane and 2-methyl-2-nitropropane. The primary purpose of this work was to extend the kinetics database to allow these compounds, M, to be analysed in air by selected ion flow tube mass spectrometry, SIFT-MS. Some nitroalkanes are used as industrial solvents and some are component of agricultural agents that are known health hazards. The initial step in all the H3O+ reactions is exothermic proton transfer to produce MH+ ions, which are seen to be the only products for the two smallest nitroalkanes, but for the isomers of nitropropane and nitrobutane, fragmentation of the nascent MH+ ions occurs. NO+ reacts with the four smallest compounds via association resulting in NO+ product ions, whilst for the isomers of nitrobutane the C4H9+ hydrocarbon ion is produced. The reaction of O-2(+.) with nitromethane proceeds via charge transfer giving M+. as the major product, whilst the O+. reactions with all the remaining nitroalkanes in this study lead to a single hydrocarbon ion product CnH2n+1 . The secondary chemistry of the ion products with H2O and with M, which is relevant to SIFT-MS applications, is fully described, with the interesting finding that water cluster ions of the kind MH+(H2O)(3) containing three water molecules are formed at 300 K. The mechanisms of the reactions are described with the aid of ab initio calculations of the ion energetics that were not previously available for some of the ions involved in the chemistry. (C) 2004 Elsevier B.V. All rights reserved.

Abstract: Selected ion flow tube mass spectrometry (SIFT-MS) has been used to analyse on-line and in real time the exhaust gas emissions from a Caterpillar 3304 diesel engine under different conditions of load (idle and 50% of rated load) and speed (910, 1500 and 2200 rpm) using three types of fuel: an ultra-low-sulphur diesel, a rapeseed methyl ester and gas oil. SIFT-MS analyses of the alkanes, alkenes and aromatic hydrocarbons in the headspace of these fuels were also performed, but the headspace of the rapeseed methyl ester consists mainly of methanol and a compound with the molecular formula C4H8O. The exhaust gases were analysed for NO and NO2 using O2+* reagent ions and for HNO2 using H3O+ reagent ions. The following aldehydes and ketones in the exhaust gases were quantified by using the combination of H3O+ and NO+ reagent ions: formaldehyde, acetaldehyde, propenal, propanal, acetone, butanal, pentanal, butanone and pentanone. Formaldehyde, acetaldehyde and pentenal, all known respiratory irritants associated with sensitisation to asthma of workers exposed to diesel exhaust, are variously present within the range 100-2000 ppb. Hydrocarbons in the exhaust gases accessible to SIFT-MS analyses were also quantified as total concentrations of the various isomers of C3H4, C3H6, C4H6, C5H8, C5H10, C6H8, C6H10, C7H14, C6H6, C7H8, C8H10 and C9H12.

Abstract: A study of the concentrations of the common breath metabolites ammonia, acetone, isoprene, ethanol and acetaldehyde in the breath of five subjects over a period of 30 days has been carried out. Breath samples were taken and analysed in the early morning on arrival at the laboratory. The real time analyses of three consecutive breath exhalations were carried out using selected ion flow tube mass spectrometry (SIFT-MS) on line to the instrument. Sufficient data were obtained to allow meaningful concentration distributions to be obtained for ammonia, acetone, isoprene and ethanol. These showed that the ammonia, acetone and isoprene concentrations exhibited sensibly normal distributions, with coefficients of variation of typically 0.3. Obvious and statistically significant (p < 0.01) differences are apparent in the mean concentrations of these metabolites between the five individuals. The acetaldehyde concentrations were relatively low and close to the instrument detection limit, and the differences between the mean concentrations of the five subjects were not statistically significant (p = 0.4), so distributions were not obtained. The mean concentrations, in parts per billion (ppb), of each metabolite range amongst the five subjects are as follows: ammonia, 422-2389: acetone, 293-870; isoprene, 55-121; ethanol, 27-153; acetaldehyde, 2-5. There are no obvious patterns in the distributions of these particular metabolites for these individuals, except that the ammonia levels were greatest in the breath of the two oldest subjects.

Abstract: INTRODUCTION: Mechanisms of water flow across the peritoneal membrane include diffusion, convection, and reabsorption. OBJECTIVES: To understand these processes more clearly we have developed a method to measure transport of water across the peritoneal membrane. METHODS: An artificial gradient of deuterated water (HDO) between blood and dialysate compartments was created in five subjects who took 0.3g per kg of body weight of D2O, which was allowed to equilibrate with total body water. During a test dwell (2 L, bicarbonate:lactate buffer, 1.36% glucose to minimize convection), frequent dialysate samples were drawn to determine the abundance of deuterium and other solutes and to calculate their time constants. Dialysate deuterium abundance was measured using flowing afterglow mass spectrometry (FA-MS). The method was combined with 125iodine-labeled albumin (RISA) to enable simultaneous estimates of intraperitoneal volume and thus calculation of the mass transfer area coefficient (MTAC) for small solutes using the Garred equation. RESULTS: The appearance of HDO in dialysate in four subjects is described by a single exponential fit with residuals of <1%, similar to method precision. In a fifth subject, the resolution of this method demonstrated that the best fit was a double exponential. When compared to other solutes, the time constant for water was as predicted by its molecular weight, with a MTAC of 38.7 +/- 4.4 mL/min. Total body water could also be estimated from the equilibrated dialysate deuterium abundance, with repeat estimates within 0.5%. CONCLUSION: Transport of water across the peritoneum can be measured with remarkable accuracy and when combined with an intraperitoneal volume estimation can be used to determine mass transfer. In conditions of low convection, the relative rate of deuterium appearance and mass transfer compared to other solutes suggests that water diffuses predominantly through the intercellular small pores.

Abstract: A selected ion flow tube mass spectrometry (SIFT-MS) study of the reactions of H3O+, NO+ and O2+* ions with the ketones (M) 2-heptanone, 2-octanone, 2-nonanone, 2-undecanone and 2-aminoacetophenone has been conducted in preparation for studies of volatile emissions from bacteria. The H3O+ reactions all proceed rapidly via exothermic proton transfer, producing only MH+ ions that form their monohydrates when water vapour is present in the helium carrier gas. The O2+* reactions proceed rapidly via dissociative charge transfer producing parent cations M+* and some fragment ions. The NO+ reactions form the NO+M adduct ions at rates which are dependent on the pressure of the helium carrier gas. Combining the present NO+ kinetic data with those available from previous SIFT studies, the phenomenon of charge transfer complexing is clearly demonstrated. This results in adduct formation in these NO+/ketone reactions at or near the collisional rate. SIFT-MS spectra are presented to illustrate the simplicity of SIFT-MS analysis of ketones using both H3O+ and NO+ precursor ions.

Abstract: The production of volatile compounds from cancer cell lines in vitro has been investigated using selected ion flow tube mass spectrometry (SIFT-MS). This technique enables on-line quantitative analyses of the headspace above cell/medium cultures. This paper reports the discovery that acetaldehyde is released by the lung cancer cell lines SK-MES and CALU-1. The concentration of acetaldehyde in the headspace of the medium/cell culture was measured after 16 h incubation at 37 degrees C and found to be proportional to the number of cancer cells in the medium (typically 10(8)). From these data, the acetaldehyde production rates of the SK-MES cells and the CALU-1 cells in vitro are determined to be 1 x 10(6) and 1.5-3 x 10(6) molecules/cell/min, respectively. The potential value of this new technique in cell biology and in industrial cell biotechnology is discussed.

Abstract: Selected ion flow tube mass spectrometry (SIFT-MS) has been used for a detailed study of the daily variations in the acetone and ammonia content of the headspace above urine from a healthy female subject over the course of three separate menstrual cycles. Midstream urine samples were taken every morning prior to any food intake and the headspace subsequently analysed for a number of metabolites. Concurrent with the time of ovulation, a 3-to- 12-fold increase in the level of acetone in the urine headspace was observed. The successive peaks in acetone level and the subsequent return to baseline values were mirrored by similar increases in the ammonia levels, but these were a day out of phase. Interestingly, parallel breath analyses at ovulation showed no great increase in either acetone or ammonia above their normal morning levels, suggesting that these metabolites had been removed from the body during the night by the usual metabolic and physiological processes. The results of this study reveal what may be an important phenomenon at the time of ovulation and illustrate the potential and power of online SIFT-MS analysis in this area of research.

Abstract: A selected ion flow tube (SIFT) study has been carried out of the reactions of hydrated nitrosonium ions, NO+H2O, which theory has equated to protonated nitrous acid ions, H2ONO+. One objective of this study was to investigate if this ion exhibits the properties of both a cluster ion and a protonated acid in their reactions with a variety of organic molecules. The chosen reactant molecules comprise two each of the following types-amines, terpenes, aromatic hydrocarbons, esters, carboxylic acids, ketones, aldehydes and alcohols. The reactant H2ONO+ (NO+H2O) ions are formed in a discharge ion source and injected into helium carrier gas where they are partially vibrationally excited and partially dissociated to NO+ ions. Hence, the reactions of the H2ONO+ ions had to be studies simultaneously with NO+ ions, the reactions of the latter ions readily being studied by selectively injecting NO+ ions into the carrier gas. The results of this study indicate that the H2ONO+ ions undergo a wide variety of reaction processes that depend on the properties of the reactant molecules such as their ionisation energies and proton affinities. These processes include charge transfer with compounds, M, that have low ionisation energies (producing M+), proton transfer with compounds possessing large proton affinities (MH+), hydride ion transfer (M-H+), alkyl radical (M-R+), alkoxide radical transfer (M-OR+), ion-molecule association (NO+H2OM) and ligand switching (NO+M), producing the ions given in parentheses. (C) 2003 Elsevier B.V. All rights reserved.

Abstract: The electron energy distribution functions for electron thermalization in helium and argon afterglow plasmas have been calculated taking into account electron-neutral and electron-electron collisions. This work shows that electron-electron collisions can lead to the Maxwellization of the electron energy distribution function and thus to different rates of electron thermalization. (C) 2003 Elsevier Science B.V. All rights reserved.

Abstract: The production of volatile compounds from cancer cell lines in vitro has been investigated using selected ion flow tube mass spectrometry (SIFT-MS). This technique enables on-line quantitative analyses of the headspace above cell/medium cultures. This paper reports the discovery that acetaldehyde is released by the lung cancer cell lines SK-MES and CALU-1. The concentration of acetaldehyde in the headspace of the medium/cell culture was measured after 16h incubation at 37degreesC and found to be proportional to the number of cancer cells in the medium (typically 10(8)). From these data, the acetaldehyde production rates of the SK-MES cells and the CALU-1 cells in vitro are determined to be 1 x 10(6) and 1.5-3 x 10(6) molecules/cell/min, respectively. The potential value of this new technique in cell biology and in industrial cell biotechnology is discussed. Copyright (C) 2003 John Wiley Sons, Ltd.

Abstract: A study of the concentrations of the common breath metabolites ammonia, acetone, isoprene, ethanol and acetaldehyde in the breath of five subjects over a period of 30 days has been carried Out. Breath samples were taken and analysed in the early morning on arrival at the laboratory. The real time analyses of three consecutive breath exhalations were carried out using selected ion flow tube mass spectrometry (SIFT-MS) on line to the instrument. Sufficient data were obtained to allow meaningful concentration distributions to be obtained for ammonia, acetone, isoprene and ethanol. These showed that the ammonia, acetone and isoprene concentrations exhibited sensibly normal distributions, with coefficients of variation of typically 0.3. Obvious and statistically significant (p < 0.01) differences are apparent in the mean concentrations of these metabolites between the five individuals. The acetaldehyde concentrations were relatively low and close to the instrument detection limit, and the differences between the mean concentrations of the five subjects were not statistically significant (p = 0.4), so distributions were not obtained. The mean concentrations, in parts per billion (ppb), of each metabolite range amongst the five subjects are as follows: ammonia, 4222389; acetone, 293-870; isoprene, 55-121; ethanol, 27-153; acetaldehyde, 2-5. There are no obvious patterns in the distributions of these particular metabolites for these individuals, except that the ammonia levels were greatest in the breath of the two oldest subjects.

Abstract: Selected ion flow tube mass spectrometry (SIFT-MS) has been used for a detailed study of the daily variations in the acetone and ammonia content of the headspace above urine from a healthy female subject over the course of three separate menstrual cycles. Midstream urine samples were taken every morning prior to any food intake and the headspace subsequently analysed for a number of metabolites. Concurrent with the time of ovulation, a 3-to-12-fold increase in the level of acetone in the urine headspace was observed. The successive peaks in acetone level and the subsequent return to baseline values were mirrored by similar increases in the ammonia levels, but these were a day out of phase. Interestingly, parallel breath analyses at ovulation showed no great increase in either acetone or ammonia above their normal morning levels, suggesting that these metabolites had been removed from the body during the night by the usual metabolic and physiological processes. The results of this study reveal what may be an important phenomenon at the time of ovulation and illustrate the potential and power of online SIFT-MS analysis in this area of research.

Abstract: The results about selected ion flow tube/mass spectrometry (SIFT/MS) study of the different compounds in petrol and diesel vapor�s using H3O+, NO+ as the precursor ions are reported. We assume both petrol and diesel are made up of CHs, including alkanes (CnH2n+2), alkenes or cyclokanes (CnH2n) alkynes or dienes (CnH2n-2) and aromatic hydrocarbons (CnH2n-6). Among these compounds, the alkanes are the predominant species both in diesel and petrol vapors; The most obvious difference between petrol and diesel vapor is. the presence of a greater abundance of long chain aliphatic CHs in the diesel vapor. In this paper, the mass spectra of petrol vapor using the precursors of the H3O+ NO+ and the quantitative analysis results of, the compounds in the petrol and diesel vapors are also presented.

Abstract: The reactions of H3O+, NO+ and O-2(+) have been studied with the 11 terpenes, myrcene, ocimene, alpha- and beta-pinene, alpha- and gamma-terpinene, 2- and 3-carene, R- and S-limonene and camphene, at thermal energies using a selected ion flow tube (SIFT). This study was intended to explore the potential of SIFT mass spectrometry (SIFT-MS), for analysing terpenes in air. All 33 reactions are seen to proceed at the collisional rate and multiple product ions result. The H3O+ reactions result in two major ion products, the stable protonated terpenes C10H17+ together with C6H9+ ions, with some minor products (a few percent) in some reactions. The NO+ reactions result in the parent cations, C10H16+, as the major product ion together with several fragment ions, notable C7H9+. The appearance of the minority adducts H3O+M and NO+M provide clues to the mechanisms of these reactions. The more energetic O-2(+) ions result in greater fragmentation and the parent terpene cations are only minority products. We conclude that SIFT-MS can only be used to estimate the concentration of total terpenes present in an air sample using H3O+ and NO+ ions, with only limited capability to distinguish between paired terpene isomers. (C) 2003 Elsevier B.V. All rights reserved.

Abstract:

Abstract: Introduction. Mechanisms of water flow across the peritoneal membrane include diffusion, convection, and reabsorption. Objectves. To understand these processes more clearly we have developed a method to measure transport of water across the peritoneal membrane. Methods. An artificial gradient of deuterated water (HDO) between blood and dialysate compartments was created in five subjects who took 0.3g per kg of body weight of D2O, which was allowed to equilibrate with total body water. During a test dwell (2 L, bicarbonate:lactate buffer, 1.36% glucose to minimize convection), frequent dialysate samples were drawn to determine the abundance of deuterium and other solutes and to calculate their time constants. Dialysate deuterium abundance was measured using flowing afterglow mass spectrometry (FA-MS). The method was combined with (125)iodine-labeled albumin (RISA) to enable simultaneous estimates of intraperitoneal volume and thus calculation of the mass transfer area coefficient (MTAC) for small solutes using the Garred equation. Results. The appearance of HDO in dialysate in four subjects is described by a single exponential fit with residuals of <1%, similar to method precision. In a fifth subject, the resolution of this method demonstrated that the best fit was a double exponential. When compared to other solutes, the time constant for water was as predicted by its molecular weight, with a MTAC of 38.7 +/- 4.4 mL/min. Total body water could also be estimated from the equilibrated dialysate deuterium abundance, with repeat estimates within 0.5%. Conclusion. Transport of water across the peritoneum can be measured with remarkable accuracy and when combined with an intraperitoneal volume estimation can be used to determine mass transfer. In conditions of low convection, the relative rate of deuterium appearance and mass transfer compared to other solutes suggests that water diffuses predominantly through the intercellular small pores.

Abstract: We have carried out a selected ion flow tube, SIFT, study of the reactions of H3O+, NO+ and O-2(+) ions with hydrogen peroxide, H2O2, in the presence of excess water vapour and peroxyacetic acid, CH3C(O)OOH, in the presence of comparable concentrations of acetic acid, CH3COOH. This study was initiated to investigate if these peroxides could be analysed in humid air using selected ion flow tube mass spectrometry, SIFT-MS, using the above precursor ions. Rate coefficients and product ions have been determined for the NO+ and O-2(+) reactions with H2O2 molecules (H3O+ ions do not react at a measurable rate with H2O2 molecules) and for the rapid reactions of H3O+, NO+ and O-2(+) with CH3C(O)OOH molecules. It turns out that both H3O+ and O-2(+) ions are unsuitable for SIFT-MS analyses of these peroxides, either because of low reactivity and/or the production of common product ions for their reactions with H2O and CH3COOH molecules. However, the results of this study show that NO+ precursor ions can be useful for the SIFT-MS analysis of both these peroxides, NO+H2O2 being the monitor ion for hydrogen peroxide analysis in moist air, the production of this ion actually being catalysed by the presence of H2O molecules, and NO2+ ion being suitable monitor ions for peroxyacetic acid analysis in the presence of acetic acid. The kinetic data for these peroxide reactions are presented and the likely mechanisms of the reactions are alluded to. (C) 2003 Elsevier Science B.V. All rights reserved.

Abstract: A study has been carried out of acetonitrile in exhaled breath and in the headspace of urine from several cigarette smokers and several non-smokers using selected ion flow tube mass spectrometry (SIFT-MS). The ion chemistry involved in the detection and quantification of acetonitrile in the gas phase by SIFT-MS using H3O+ ions is outlined. Further to this, experiments have been carried out to determine the Henry�s Law partition coefficients for dilute aqueous solutions of acetonitrile, which allow the determination of liquid phase urinary acetonitrile concentrations from headspace concentrations. The results of this study show that acetonitrile is readily detected by SIFT-MS in the breath and urinary headspace of smokers at levels dependent on the cigarette consumption, but is practically absent from the breath and urine headspace of non-smokers. Exploiting the measured values of the Henry�s Law partition coefficients, the urinary phase concentrations have been deduced. The results of this study show that typical breath concentrations of acetonitrile are within the range 17-124 ppb (mean value 69 ppb), which are in close agreement with previous studies. The urinary acetonitrile concentrations are within the range 0-150 mug/L (mean value 57 mug/L), which are close to the concentrations determined previously in blood. These collected data imply that the acetonitrile is equilibrated amongst the body fluids (blood, total body water and urine) and that excretion occurs via both exhaled breath and urine. (C) 2003 Elsevier Science B.V. All rights reserved.

Abstract: A selected ion flow tube mass spectrometry (SIFT-MS) study of the reactions of H3O+, NO+ and O-2(+) ions with the ketones (M) 2-heptanone, 2-octanone, 2-nonanone, 2-undecanone and 2-aminoacetophenone has been conducted in preparation for studies of volatile emissions from bacteria. The H3O+ reactions all proceed rapidly via exothermic proton transfer, producing only MH+ ions that form their monohydrates when water vapour is present in the helium carrier gas. The O-2(+) reactions proceed rapidly via dissociative charge transfer producing parent cations M+ and some fragment ions. The NO+ reactions form the NO+M adduct ions at rates which are dependent on the pressure of the helium carrier gas. Combining the present NO+ kinetic data with those available from previous SIFT studies, the phenomenon of charge transfer complexing is clearly demonstrated. This results in adduct formation in these NO+/ketone reactions at or near the collisional rate. SIFT-MS spectra are presented to illustrate the simplicity of SIFT-MS analysis of ketones using both H3O+ and NO+ precursor ions. Copyright (C) 2003 John Wiley Sons, Ltd.

Abstract: We have carried out a study of the reactions of H3O+, NO+ and O-2(+). the commonly used precursor ions for selected ion flow tube mass spectrometry (SIFT-MS), with three anaesthetic gases, halothane, isoflurane and sevoflurane. The motivation for this study was to provide the necessary kinetic data that would allow the quantification of these anaesthetic gases in operating theatre air and in the breath of theatre staff and post-operative patients. A clear negative result from these experiments is that NO+, although undergoing the simplest chemistry, is unsuitable for this SIFT-MS application. However, although the ion chemistry of H3O+ and O-2(+) with these compounds is very complex, there being several product ions in each reaction, many of which react rapidly with water molecules, monitor ions have been identified for all three anaesthetic gases when using H3O+ and O-2(+) as precursor ions. The detailed ion chemistry is discussed and the specific monitor ions are indicated. Hence, the feasibility of on-line breath monitoring is demonstrated by simple examples. These studies have opened the way to measurements in the clinical environment. Copyright (C) 2002 John Wiley Sons, Ltd.

Abstract: We have used selected ion flow tube mass spectrometry (SIFT-MS) to analyse the vapours emitted by petrol and diesel fuels and the exhaust gases from petrol (spark ignition) and diesel (compression ignition) engine vehicles fitted with catalytic converters. Only those components of these media that have significant vapour pressures at ambient temperatures were analysed and thus particulates were obviously not detected. These media have been analysed using the full scope of SIFT-MS, i.e., with the three available precursor ions H3O+, NO+ and O-2(+). The combination of the H3O+ and NO+ analyses is seen to be essential to distinguish between different product ions at the same mass-to-charge ratio (m/z) especially in identifying aldehydes in the exhaust gases. The O-2(+) precursor ions are used to detect and quantify the large amount of nitric oxide present in the exhaust gases from both engine types. The petrol and diesel vapours consist almost exclusively of aliphatic alkanes, alkenes and alkynes (and dienes) and aromatic hydrocarbons. Some of these compounds appear in the exhaust gases together with several aldehydes, viz. formaldehyde, acetaldehyde, pentanal, pentenal (acrolein), butenal, and also methanol and ethanol. Acetone, nitric oxide and ammonia are also present, acetone and nitric oxide being much more abundant in the diesel exhaust gas than in the petrol exhaust gas. These data were obtained from samples collected into pre-evacuated stainless steel vessels. Trapping of the volatile compounds from the gas samples is not required and analysis was completed a few minutes later. All the above compounds are detected simultaneously, which demonstrates the value of SIFT-MS in this area of research. Copyright (C) 2002 John Wiley Sons, Ltd.

Abstract: We have carried out a selected ion flow tube (SIFT) study of the reactions of H3O+, NO+, and O-2(+) ions with several saturated and unsaturated aldehydes. This study is mainly directed toward providing the essential data for a projected SIFT mass spectrometry (SIFTMS) study of the volatile emissions from cooked meats, which always include aldehydes. Thus, it is necessary to know the rate coefficients and the product ions of the reactions of the above-mentioned ions, used as the precursor ions for SIFTMS analyses, with the aldehydes, if proper identification and quantification of the emitted species are to be achieved, The results of this study show that the reactions of H3O+ with the aldehydes, M, result in the protonated molecules MH+ and for the saturated aldehydes also in (M - OH)(+) ions resulting from the loss of a H2O molecule from the nascent MH+ ion. The NO+ reactions invariably proceed via the process of hydride ion, H-, transfer producing (M - H)(+) ions, but parallel minor association product ions NO+ (.) M are observed for some of the unsaturated aldehyde reactions. The O-2(+) reactions proceed by way of charge transfer producing nascent M+ ions that partially dissociate producing fragment ions. Because water vapour is invariably present in real samples analysed by SIFTMS, the current experiments were also carried out following the introduction of humid laboratory air into the helium carrier gas of the SIFT Thus, the reactions of the product ions that form hydrates were also studied as a prelude to future SIFTMS studies of the (humid) emissions from cooked meats. (Int J Mass Spectrom 213 (2002) 163-176) (C) 2002 Elsevier Science B.V.

Abstract: We have carried out Monte Carlo simulation of the motion of Ar+ ions in the space charge sheath surrounding a cylindrical Langmuir probe. The ion currents to the probe have been calculated from these simulations and the percentages of ions crossing the sheath boundary that are collected by the probe have been determined. It has been shown that the collisions of ions with neutral helium gas atoms in the sheath increase the percentage of ions collected by the probe above that predicted by collisionless orbital motion limited current (OMLC) theory at lower helium pressure and decrease this percentage below the OMLC theory prediction at higher helium pressure. It has been shown also that the ion current almost does not depend on probe radius at higher helium pressures. The results of the simulations have been compared with recent Langmuir probe measurements made in flowing afterglow plasmas and with other probe theories.

Abstract: As a prelude to investigations of the emission of metabolites from human cell lines in vitro, we have conducted a study using selected ion flow tube mass spectrometry (SIFT-MS) of the acetaldehyde and ethanol that appear in the headspace above a fermenting yeast/glucose/water mixture in sealed glass bottles at a temperature of 30 degreesC. A fixed quantity of yeast (10 mg) and varying amounts (2, 4, 8 and 16 mg) of both non-deuterated glucose and glucose-6,6-d(2) in 5 mL of water were used and the emission of the acetaldehyde and the ethanol were observed as a function of time. The ethanol and acetaldehyde concentrations in the headspace were obtained from the magnitudes of their characteristic ions on the accumulated SIFT mass spectra and, when the deuterated glucose was used, characteristic singly and doubly deuterated ions were obvious. This study indicates, as expected, that ethanol is the major species generated and that acetaldehyde is a relatively minor component of the headspace and a very minor component of the liquid phase. We estimate that about 10(s) ethanol molecules are produced per minute per cell in this yeast fermentation process. The distribution of the non-deuterated and partially deuterated ethanol under these fermentation conditions is observed to be C2H5OH (66 +/- 4)%, C2H4DOH(6 +/- 1)%, C2H3D2OH(28 +/- 4)%, and the analogous distribution for the acetaldehyde is the same, within error. These results indicate that the D atoms in the glucose-6,6-d(2) are mostly retained by the 6-C atom, but the appearance of the singly deuterated ethanol and acetaldehyde indicates that some D/H mixing must be occurring in the enzymatic reactions. The results of this study illustrate the potential and power of on-line SIFT-MS analysis in this area of research. Copyright (C) 2001 John Wiley & Sons, Ltd.

Abstract: We report the results of a detailed selected ion flow tube (SIFT) study at 300 K of the reactions of the 1-alkene and trans-2-alkene isomers of pentene, hexene, heptene, octene and nonene and I-decene (all liquids at room temperature) with H3O+, NO+ and O-2(+). All 33 reactions proceeded at the collisional rate under these SIFT conditions (helium carrier gas pressure of 0.7 Torr). The H3O+ reactions with both isomers of each alkene proceeded via exothermic proton transfer, which resulted in partial dissociation of the MH+ product ions for the longer chain alkene molecules, M, the number of fragment ions depending on the chain length. However, the mechanisms of the NO+ reactions were isomer specific, those involving the 1-alkenes proceeded via NO+ M production (three-body association) followed by partial stabilisation and partial dissociation of the nascent adduct ion to several products, including ions of the kind RHNO+ (R = CH3, C3H5, C4H7, etc,), whilst those involving the trans-2-alkene isomers proceeded partially via charge (electron) transfer to give M+ parent ions and via hydride ion (H-) transfer giving (M-H)(+) ions. The O-2(+) reactions all proceeded via charge transfer to give M+ ions together with multiple fragment ions. These O-2(+) SIFT data are compared and contrasted with the corresponding electron ionisation spectra (from the NIST database) for these alkenes. (C) 2002 Elsevier Science B.V. All rights reserved.

Abstract: A selected ion flow tube study has been carried out of the reactions of H3O+, NO+ and O-2(+) with 1,2-ethanediol (ethylene glycol), 1,2- and 1,3-propanediol, 1,2-, 1,3- and 1,4-butanediol, 1,5-pentanediol, 1,2-cyclopentanediol and 2-thioethanol (or 2-mercapto-ethanol, HOCH2CH2SH). The reactions of these species with H3O+ ions are assumed to proceed via exothermic proton transfer, their rate coefficients, k(c) being equal to the calculated collisional rate coefficients, k(c). On this basis, the experimental k values for most of the NO+ and O-2(+) reactions are also close to their respective k(c) values, although the k values for three of the NO+ reactions are measurably smaller than their k(c) values. In the H3O+ reactions the protonated parent ions , MH+, are always minor product ions. (MH-H2O)(+), resulting from the loss of H2O from the nascent MH+ ions being the major product ions. Three-body rate coefficients are derived for the association reactions of these product ions with water molecules. The most common process that occurs in the NO+ reactions is hydride ion transfer producing (M-H)(+) ions, but for the 1,4-butanediol and 1,5-pentanediol reactions, hydride ion transfer and parallel H2O elimination occur. The O-2(+) reactions all lead to multiple product ions, which must result from very diverse fragmentation processes. The value to selected ion flow tube mass spectrometry of these kinetic data is briefly alluded to. (Int J Mass Spectrom 218 (2002) 227-236) (C) 2002 Elsevier Science B.V. All rights reserved.

Abstract: We describe a method by which the concentrations of volatile compounds in the headspace of their dilute aqueous solutions in sealed containers can be determined using on-line selected ion flow tube mass spectrometry (SIFT-NIS). Thus, the changing number density of the molecules of the volatile compound in the carrier gas of the SIFT-MS instrument is described in terms of its changing flow rate as the pressure in the sealed container decreases during the sampling procedure. It is shown that the best analytical procedure is to determine the mean concentration of the trace gas in the liquid headspace over a given sampling time and relate this to the required concentration, which is the initial equilibrium concentration established before the pressure in the sealed container reduces significantly. To test the validity of this analytical approach, the headspace concentrations of acetaldehyde, ethanol and acetone above aqueous solutions of known concentrations have been determined. Hence, the Henry�s Law constants for these compounds have been determined and found to agree with the published values. The confirmation of the quality of this sampling methodology combined with SIFT-MS for the analysis of volatile compounds in liquid headspace paves the way for the rapid analyses of biological liquids such as urine and serum for clinical diagnosis and physiological monitoring. Copyright (C) 2002 John Wiley Sons, Ltd.

Abstract:

Abstract: Selected ion flow tube mass spectrometry, SIFT-MS, has been used to measure simultaneously the concentrations in exhaled breath of ethanol, acetaldehyde, ammonia, acetone and, routinely, water vapour, following the ingestion of various amounts of ethanol in 500 ml of water. These breath analyses were obtained from only single exhalations, the results being available immediately in real time. The breath ethanol reaches concentrations that are only approximately consistent with its dilution in blood and body water. For moderate ethanol doses the decay quickly exhibits first-order kinetics (a single exponential decay) whereas for relatively large ethanol doses, the initial decay of ethanol from the breath is slow, indicating saturation kinetics. For smaller doses, and following a meal, the breath ethanol increases only slightly indicating that it is largely metabolized in the stomach. We suggest that the time delay (following ethanol ingestion) before the breath ethanol begins to increase is an indicator of the gastric emptying rate. Then the rate of decay of ethanol from the breath/blood is related to its rate of metabolism subsequent to its dispersal into the body water. The much lower breath acetaldehyde levels correlate well with the ethanol levels indicating that it is mostly formed from the metabolism Of the ethanol. The breath ammonia is seen to �dip� following the water/alcohol drink and this is consistent with previous work in which this same phenomenon was observed following the ingestion of comparable volumes of liquid meals. The simultaneous breath acetone concentrations increase somewhat with time as is expected during the fasting state. The water vapour measurements are indicators of the precision and accuracy of the breath analyses, these being sufficient to show the differences between the breath (body) temperatures of the individuals of less than 1 degreesC. This study demonstrates the potential of SIFT-MS for non-invasive physiological measurement.

Abstract: Background: We developed a new near-subject approach, using flowing afterglow-mass spectrometry (FA-MS) and deuterium dilution, which enables the immediate measurement of total body water (TBW) from single exhalations. Objectives: The objectives were to show the efficacy of the new FA-MS method in measuring TBW in healthy subjects and to compare these measurements with values derived from multifrequency bioelectrical impedance analysis, skinfold-thickness (SFT) measurements, and both recent and historical published regression equations. Design: After baseline measurement of breath deuterium abundance, 24 healthy subjects ingested 0.3 g D2O/kg body wt. A second breath sample was taken after 3 h to measure the increase in deuterium, from which TBW was calculated. Bioelectrical impedance analysis was carried out with a multifrequency analyzer, and SFT was measured by a single trained observer. Methods were compared with the use of Pearson�s correlation coefficient and Bland-Altman analyses. Results: TBW measures obtained by all methods were highly correlated (r = 0.95-0.98, P < 0.001), especially those between FA-MS, SFT measurement, and recent regression equations. The mean values obtained were within 2% of those published for age-matched control subjects and varied by 1-6% when all methods were compared. Systematic bias was greatest when FA-MS was compared with bioelectrical impedance analysis, which tended to underestimate TBW in smaller, female subjects. No bias related to subject size was observed in a comparison of FA-MS with SFT measurement or with more recent regression equations. Conclusions: FA-MS is a simple and effective new approach to TBW measurement in healthy subjects. The difficulty of using population-derived equations to estimate TBW in individual subjects is emphasized.

Abstract: A quadrupole mass spectrometer was used to diagnose the ionic products from the microwave discharge through a mixture of air and water vapor. H3O+, NO+ and O-2(+), important primary reagent ions in the chemical ionization mass spectrometry (SIFT-MS) were observed at ionic beam current of up to 10 nA. The formation mechanisms for the above ions generated in the discharge were analyzed in conjunction with the ions detectied in the cases of N-2, O-2 and H2O microwave discharges, respectively. Thus, various ion-molecule reactions involving the primary ions N-2(+),. N+, O-2(+), O+, H2O+ and OH+ were proposed to be responsible for the formation of H3O+, NO+ and O-2(+), which were also demonstrated by computer simulation based on such ion-molecule reactions.

Abstract: Selected ion flow tube mass spectrometry, SIFT-MS, has been used to measure simultaneously the concentrations in exhaled breath of ethanol, acetaldehyde, ammonia, acetone and, routinely, water vapour, following the ingestion of various amounts of ethanol in 500 ml of water. These breath analyses were obtained from only single exhalations, the results being available immediately in real time. The breath ethanol reaches concentrations that are only approximately consistent with its dilution in blood and body water. For moderate ethanol doses the decay quickly exhibits first-order kinetics (a single exponential decay) whereas for relatively large ethanol doses, the initial decay of ethanol from the breath is slow, indicating saturation kinetics. For smaller doses, and following a meal, the breath ethanol increases only slightly indicating that it is largely metabolized in the stomach. We suggest that the time delay (following ethanol ingestion) before the breath ethanol begins to increase is an indicator of the gastric emptying rate. Then the rate of decay of ethanol from the breath/blood is related to its rate of metabolism subsequent to its dispersal into the body water. The much lower breath acetaldehyde levels correlate well with the ethanol levels indicating that it is mostly formed from the metabolism of the ethanol. The breath ammonia is seen to 'dip' following the water/alcohol drink and this is consistent with previous work in which this same phenomenon was observed following the ingestion of comparable volumes of liquid meals. The simultaneous breath acetone concentrations increase somewhat with time as is expected during the fasting state. The water vapour measurements are indicators of the precision and accuracy of the breath analyses, these being sufficient to show the differences between the breath (body) temperatures of the individuals of less than 1 degrees C. This study demonstrates the potential of SIFT-MS for non-invasive physiological measurement.

Abstract: We have carried out a study of the reactions of H(3)O(+), NO(+) and O(2) (+), the commonly used precursor ions for selected ion flow tube mass spectrometry (SIFT-MS), with three anaesthetic gases, halothane, isoflurane and sevoflurane. The motivation for this study was to provide the necessary kinetic data that would allow the quantification of these anaesthetic gases in operating theatre air and in the breath of theatre staff and post-operative patients. A clear negative result from these experiments is that NO(+), although undergoing the simplest chemistry, is unsuitable for this SIFT-MS application. However, although the ion chemistry of H(3)O(+) and O(2) (+) with these compounds is very complex, there being several product ions in each reaction, many of which react rapidly with water molecules, monitor ions have been identified for all three anaesthetic gases when using H(3)O(+) and O(2) (+) as precursor ions. The detailed ion chemistry is discussed and the specific monitor ions are indicated. Hence, the feasibility of on-line breath monitoring is demonstrated by simple examples. These studies have opened the way to measurements in the clinical environment.

Abstract: We have used selected ion flow tube mass spectrometry (SIFT-MS) to analyse the vapours emitted by petrol and diesel fuels and the exhaust gases from petrol (spark ignition) and diesel (compression ignition) engine vehicles fitted with catalytic converters. Only those components of these media that have significant vapour pressures at ambient temperatures were analysed and thus particulates were obviously not detected. These media have been analysed using the full scope of SIFT-MS, i.e., with the three available precursor ions H3O+, NO+ and O2+. The combination of the H3O+ and NO+ analyses is seen to be essential to distinguish between different product ions at the same mass-to-charge ratio (m/z) especially in identifying aldehydes in the exhaust gases. The O2+ precursor ions are used to detect and quantify the large amount of nitric oxide present in the exhaust gases from both engine types. The petrol and diesel vapours consist almost exclusively of aliphatic alkanes, alkenes and alkynes (and dienes) and aromatic hydrocarbons. Some of these compounds appear in the exhaust gases together with several aldehydes, viz. formaldehyde, acetaldehyde, pentanal, pentenal (acrolein), butenal, and also methanol and ethanol. Acetone, nitric oxide and ammonia are also present, acetone and nitric oxide being much more abundant in the diesel exhaust gas than in the petrol exhaust gas. These data were obtained from samples collected into pre-evacuated stainless steel vessels. Trapping of the volatile compounds from the gas samples is not required and analysis was completed a few minutes later. All the above compounds are detected simultaneously, which demonstrates the value of SIFT-MS in this area of research.

Abstract: As a prelude to investigations of the emission of metabolites from human cell lines in vitro, we have conducted a study using selected ion flow tube mass spectrometry (SIFT-MS) of the acetaldehyde and ethanol that appear in the headspace above a fermenting yeast/glucose/water mixture in sealed glass bottles at a temperature of 30 degrees C. A fixed quantity of yeast (10 mg) and varying amounts (2, 4, 8 and 16 mg) of both non-deuterated glucose and glucose-6,6-d2 in 5 mL of water were used and the emission of the acetaldehyde and the ethanol were observed as a function of time. The ethanol and acetaldehyde concentrations in the headspace were obtained from the magnitudes of their characteristic ions on the accumulated SIFT mass spectra and, when the deuterated glucose was used, characteristic singly and doubly deuterated ions were obvious. This study indicates, as expected, that ethanol is the major species generated and that acetaldehyde is a relatively minor component of the headspace and a very minor component of the liquid phase. We estimate that about 10(8) ethanol molecules are produced per minute per cell in this yeast fermentation process. The distribution of the non-deuterated and partially deuterated ethanol under these fermentation conditions is observed to be C2H5OH (66 +/- 4)%, C2H4DOH(6 +/- 1)%, C2H3D2OH(28 +/- 4)%, and the analogous distribution for the acetaldehyde is the same, within error. These results indicate that the D atoms in the glucose-6,6-d2 are mostly retained by the 6-C atom, but the appearance of the singly deuterated ethanol and acetaldehyde indicates that some D/H mixing must be occurring in the enzymatic reactions. The results of this study illustrate the potential and power of on-line SIFT-MS analysis in this area of research.

Abstract: BACKGROUND: We developed a new near-subject approach, using flowing afterglow-mass spectrometry (FA-MS) and deuterium dilution, which enables the immediate measurement of total body water (TBW) from single exhalations. OBJECTIVES: The objectives were to show the efficacy of the new FA-MS method in measuring TBW in healthy subjects and to compare these measurements with values derived from multifrequency bioelectrical impedance analysis, skinfold-thickness (SFT) measurements, and both recent and historical published regression equations. DESIGN: After baseline measurement of breath deuterium abundance, 24 healthy subjects ingested 0.3 g D(2)O/kg body wt. A second breath sample was taken after 3 h to measure the increase in deuterium, from which TBW was calculated. Bioelectrical impedance analysis was carried out with a multifrequency analyzer, and SFT was measured by a single trained observer. Methods were compared with the use of Pearson's correlation coefficient and Bland-Altman analyses. RESULTS: TBW measures obtained by all methods were highly correlated (r = 0.95-0.98, P < 0.001), especially those between FA-MS, SFT measurement, and recent regression equations. The mean values obtained were within 2% of those published for age-matched control subjects and varied by 1-6% when all methods were compared. Systematic bias was greatest when FA-MS was compared with bioelectrical impedance analysis, which tended to underestimate TBW in smaller, female subjects. No bias related to subject size was observed in a comparison of FA-MS with SFT measurement or with more recent regression equations. CONCLUSIONS: FA-MS is a simple and effective new approach to TBW measurement in healthy subjects. The difficulty of using population-derived equations to estimate TBW in individual subjects is emphasized.

Abstract: We describe a method by which the concentrations of volatile compounds in the headspace of their dilute aqueous solutions in sealed containers can be determined using on-line selected ion flow tube mass spectrometry (SIFT-MS). Thus, the changing number density of the molecules of the volatile compound in the carrier gas of the SIFT-MS instrument is described in terms of its changing flow rate as the pressure in the sealed container decreases during the sampling procedure. It is shown that the best analytical procedure is to determine the mean concentration of the trace gas in the liquid headspace over a given sampling time and relate this to the required concentration, which is the initial equilibrium concentration established before the pressure in the sealed container reduces significantly. To test the validity of this analytical approach, the headspace concentrations of acetaldehyde, ethanol and acetone above aqueous solutions of known concentrations have been determined. Hence, the Henry's Law constants for these compounds have been determined and found to agree with the published values. The confirmation of the quality of this sampling methodology combined with SIFT-MS for the analysis of volatile compounds in liquid headspace paves the way for the rapid analyses of biological liquids such as urine and serum for clinical diagnosis and physiological monitoring.

Abstract: Selected ion flow tube mass spectrometry, (SIFT-MS), involves the partial conversion of mass-selected precursor ions to product ions in their reactions with the trace gases in an air sample that is introduced into helium carrier gas in a flow tube. The precursor and product ions are then detected and counted by a downstream quadrupole mass spectrometer. Quantification of particular trace gases is thus achieved from the ratio of the total count rate of the product ions to that for the precursor ions. However, it is important to appreciate that in this ion chemistry the light precursor ions (usually H3O+ ions) are invariably converted to heavier product ions. Hence, the product ions diffuse to the flow tube walls more slowly and thus they are more efficiently transported to the downstream mass spectrometer sampling orifice. This phenomenon we refer to as diffusion enhancement. Further, it is a well-known fact that discrimination can occur against ions of large mass-to-charge ratio, (m/z), in quadrupole mass spectrometers. If not accounted for, diffusion enhancement usually results in erroneously high trace gas concentrations and mass discrimination results in erroneously low concentrations. In this experimental investigation, we show how both these counteracting effects can be accounted for to increase the accuracy of SIFT-MS quantification. This is achieved by relating the currents of ions of various m/z that arrive at the downstream mass spectrometer sampling orifice disc to their count rates at the ion detector after mass analysis. Thus, both diffusion enhancement and mass discrimination are parameterized as a function of m/z and these are combined to provide an overall discrimination factor for the particular analytical instrument.

Abstract: The ability to measure total body water accurately, non-invasively and rapidly with results that are immediately available would represent an important advance in body composition research. Flowing afterglow mass spectrometry (FA-MS) has been developed to enable immediate measurement of deuterium content in breath water from single exhalations, which when combined with oral D2O loading enables measurement of total body water. We report here its first use in normal subjects, demonstrating the dispersal kinetics of deuterium in the body by monitoring deuterium in breath water following ingestion. Ten studies were performed in six normal subjects. After obtaining baseline samples, each subject ingested 0.3 g x kg(-1) of 99.9% pure D2O. Subsequently, breath samples were obtained every 3-5 minutes until equilibration had occurred. Three distinct phases in breath deuterium content were observed: an initial immediate peak due to HDO remaining in the oral cavity, a secondary peak reflecting gastrointestinal absorption and finally equilibration with the body water. The incremental increase in breath deuterium abundance between baseline and equilibration was used to calculate the total body water. Mathematical fitting of this final equilibration phase demonstrated that the measured deuterium abundance was within 0.2% of the ideal (asymptotic) value within 2 hours in all cases. We conclude that FA-MS is a powerful new method that, when combined with oral D2O loading, enables measurement of the dispersal kinetics of HDO and the calculation of total body water within 2 hours.

Abstract: The ability to measure total body water accurately, non-invasively and rapidly with results that are immediately available would represent an important advance in body composition research. Flowing afterglow mass spectrometry (FA-MS) has been developed to enable immediate measurement of deuterium content in breath water from single exhalations. which when combined with oral D2O loading enables measurement of total body water. We report here its first use in normal subjects, demonstrating the dispersal kinetics of deuterium in the body by monitoring deuterium in breath water following ingestion. Ten studies were performed in six normal subjects. After obtaining baseline samples, each subject ingested 0.3 g kg(-1) of 99.9% pure D2O. Subsequently, breath samples were obtained every 3-5 minutes until equilibration had occurred. Three distinct phases in breath deuterium content were observed: an initial immediate peak due to HDO remaining in the oral cavity, a secondary peak reflecting gastrointestinal absorption and finally equilibration with the body water. The incremental increase in breath deuterium abundance between baseline and equilibration was used to calculate the total body water. Mathematical fitting of this final equilibration phase demonstrated that the measured deuterium abundance was within 0.2% of the ideal (asymptotic) value within 2 hours in all cases. We conclude that FA-MS is a powerful new method that, when combined with oral D2O loading, enables measurement of the dispersal kinetics of HDO and the calculation of total body water within 2 hours.

Abstract: We have assessed the accuracy and precision of our flowing afterglow mass spectrometric method (FA-MS) for absolute measurements of deuterium abundance in water using standardised tap water/ D2O mixtures within the D/H range from 155 ppm (local tap water) to 1104 ppm, prepared by the gravimetric method. The results of this study show that a precision and accuracy of 1% can be achieved for the deuterium abundance in water samples. This is quite adequate for the main application, which is the rapid, non-invasive measurement of total body water by deuterium analysis of breath water vapour using the D2O dilution method. Copyright (C) 2001 John Wiley & Sons, Ltd.

Abstract: Attachment rate coefficients, beta, and product ion distributions, R, have been determined for the chlorobromomethanes CHCl2Br, CCl2Br2, and CHClBr2 using the flowing afterglow/Langmuir probe (FALP) method. Thus beta and R have been determined at two attaching gas temperatures, T-g, of 300 K and 540 K and at electron temperatures, T-e, ranging from T-g to about 5000 K, The results show that T-g rather than T-e has the stronger influence on both beta and R and that Br- ions are the major products of these three reactions. Both beta and Cl- increase markedly with T-g, but the variations of beta and R with T-e, although not so straightforward, are nevertheless well defined. Thus, it is apparent that dissociation to reaction products of the nascent negative ions is efficiently promoted by Dreheating. the attaching molecules (increasing T-g). and to a lesser extent by increasing T-e, which is generally In accordance with a model we previously developed to describe other haloalkane attachment reactions. Electron capture by CHCl2Br and CCl2Br2 vary with T-e as predicted by capture rate theory, whereas autodetachment apparently seriously decreases the effective capture rate by CHClBr2. By combining beta and R values for these reactions under truly thermalised conditions, the partial rate coefficients for the Br- and Cl- reaction channels have been derived and from their variation with T-g, Arrhenius activation energies for Br- and Cl- production have been estimated. Small fractions of dihalogen negative ions are produced in these attachment reactions with ClBr- ions representing a significant fraction of the product ion distribution for the CHClBr2 reaction, (Int J Mass Spectrom 205 (2001) 243-252) (C) 2001 Elsevier Science B.V.

Abstract: We have developed a new method for the on-line quantification of deuterium in water vapour. We call this method flowing afterglow mass spectrometry (FA-MS). A swarm of H3O+ precursor ions is created in flowing helium carrier gas by a microwave discharge. These precursor ions react with the H2O, HDO, (H2O)-O-17 and (H2O)-O-18 molecules in a water vapour sample that is introduced into the carrier gas/H3O+ ion swarm. The hydrated ions, H3O+ (H2O)(3) at m/z 73, and their isotopic variant ions H8DO4+ and (H9OO3+)-O-17 at m/z 74 and (H9OO3+)-O-18 at m/z 75, are thus formed. By adopting the known fractional abundance of O-18 in water vapour, and accounting for the contribution of the isotopic ions (H9OO3+)-O-17 to the ion signal at m/z 74, a measurement of the 74/75 ion signal ratio under equilibrium conditions provides the fractional deuterium abundance in the water vapour sample. Using this technique, the deuterium abundance in the water vapour present in single exhalations of breath can be determined. Thus, from the temporal variations of breath deuterium following the ingestion of a known quantity of D2O, we show that total body water can be determined non-invasively and the kinetics of water flow around the body can be tracked. Copyright (C) 2001 John Wiley & Sons, Ltd.

Abstract: Background. Isoprene is the most abundant hydrocarbon present in breath, and recent reports indicate that breath concentrations increase following haemodialysis. The purpose of this study was to establish whether selected ion flow tube mass spectrometry (SIFT-MS), a newly established technique in breath analysis, may be used to quantify breath isoprene in haemodialysis patients in the clinical setting. SIFT-MS is compared and contrasted with the established gas chromatography mass spectrometric technique for this purpose. Methods. Three consecutive exhalations from 19 haemodialysis patients (12 males, seven females) undergoing a morning dialysis shift were analysed just prior to commencing treatment. Within 5 min of completing their usual dialysis regimen, using polysulphone membranes, the breath of each patient was analysed again. Additional contemporary samples were obtained from 17 normal controls. Breath isoprene was quantified using SIFT-MS, a method previously validated quantitatively using neat isoprene. Results. Successful measurements of breath isoprene were obtained for each subject within 2 min, with minimum disruption to a busy dialysis environment. The coefficient of variation of triplicate measurements of breath isoprene was < 10%. Prior to dialysis, the mean (+/- SD) breath isoprene concentration (138 +/- 63 parts per billion (ppb)) was significantly greater than for normal controls (89 +/- 36 ppb; P = 0.016). Immediately following treatment, breath isoprene increased significantly to 184 +/- 95 ppb (P = 0.023). Conclusions. SIFT-MS permits the accurate and rapid measurement of breath isoprene in haemodialysis patients in the clinical setting. The previously reported increase in breath isoprene following dialysis treatment is confirmed. SIFT-MS is the ideal analytical tool to investigate this phenomenon further.

Abstract: We describe how selected ion flow tube mass spectrometry (SIFT-MS) can be used to determine the absolute humidity of air, breath and liquid headspace samples. This involves the determination of the relative count rates of the H3O+ ions and those H3O+. (H2O)(1,2,3) hydrate ions that inevitably form in the helium carrier gas when humid samples are being analysed by SIFT-MS using H2O+ precursor ions. This requires an understanding of the kinetics of hydrated hydronium ion formation, the involvement of mass discrimination in the analytical quadrupole mass spectrometer and the decreased diffusive loss of the heavier hydrates along the flow tube. Thus, we show that the humidity of breath and liquid headspace samples, typically at the few percent level, can be directly obtained on-line to the SIFT-MS instrument along with the concentrations of trace gases, which are present at much lower levels. We emphasise the value of parallel humidity measurements in ensuring good real-time sampling of breath and liquid headspace and the value of such measurements to trace gas analysis using SIFT-MS. Copyright (C) 2001 John Wiley & Sons, Ltd.

Abstract: This work investigated the potential to use measurement of the concentration of certain gases in the rumen headspace to gain information about rumen processes and as a potential diagnostic tool. We used new equipment (selected-ion-flow-tube mass spectrometer) that allows rapid and precise analysis of many of the gases present in a sample. Samples of rumen headspace gas and corresponding samples of rumen liquor were taken from three lactating cows, prepared with rumen fistulae, at intervals after receiving their morning feed allocation (grass silage and concentrates). Hydrogen sulfide, methyl sulfide, and dimethyl sulfide, were the predominant gases that were measured in the rumen headspace by this technique. The concentrations of these sulfur compounds declined over the interval after feeding, mirroring ammonia concentrations measured in rumen liquor, reflecting their common dependence on the fermentation of sulfur amino acids. Ammonia concentrations in rumen headspace gas varied in the opposite direction to the concentration of ammonia in rumen liquor and likely depend more on the pH of rumen liquor. Consideration of the pKa of ammonia suggests that ammonia concentrations in rumen gas will be very low below pH 6, representing a useful diagnostic for subacute ruminal acidosis. Low concentrations of volatile fatty acids were detected in rumen gas. The molar proportions of volatile fatty acids were similar in gas and liquor samples, with rumen gas containing slightly less acetic acid and disproportionately more valeric and caproic acids.

Abstract: This work investigated the potential to use measurement of the concentration of certain gases in the rumen headspace to gain information about rumen processes and as a potential diagnostic tool. We used new equipment (selected-ion-flow-tube mass spectrometer) that allows rapid and precise analysis of many of the gases present in a sample. Samples of rumen headspace gas and corresponding samples of rumen liquor were taken from three lactating cows, prepared with rumen fistulae, at intervals after receiving their morning feed allocation (grass silage and concentrates). Hydrogen sulfide, methyl sulfide, and dimethyl sulfide, were the predominant gases that were measured in the rumen headspace by this technique. The concentrations of these sulfur compounds declined over the interval after feeding, mirroring ammonia concentrations measured in rumen liquor, reflecting their common dependence on the fermentation of sulfur amino acids. Ammonia concentrations in rumen headspace gas varied in the opposite direction to the concentration of ammonia in rumen liquor and likely depend more on the pH of rumen liquor. Consideration of the pK(a) of ammonia suggests that ammonia concentrations in rumen gas will be very low below pH 6, representing a useful diagnostic for subacute ruminal acidosis. Low concentrations of volatile fatty acids were detected in rumen gas. The molar proportions of volatile fatty acids were similar in gas and liquor samples, with rumen gas containing slightly less acetic acid and disproportionately more valeric and caproic acids.

Abstract: Selected ion flow tube mass spectrometry, (SIFT-MS), involves the partial conversion of mass-selected precursor ions to product ions in their reactions with the trace gases in an air sample that is introduced into helium carrier gas in a flow tube. The precursor and product ions are then detected and counted by a downstream quadrupole mass spectrometer. Quantification of particular trace gases is thus achieved from the ratio of the total count rate of the product ions to that for the precursor ions. However, it is important to appreciate that in this ion chemistry the Light precursor ions (usually H,Of ions) are invariably converted to heavier product ions. Hence, the product ions diffuse to the flow tube walls more slowly and thus they are more efficiently transported to the downstream mass spectrometer sampling orifice. This phenomenon we refer to as diffusion enhancement. Further, it is a well-known fact that discrimination can occur against ions of large mass-to-charge ratio, (m/z), in quadrupole mass spectrometers. If not accounted for, diffusion enhancement usually results in erroneously high trace gas concentrations and mass discrimination results in erroneously low concentrations. In this experimental investigation, we show how both these counteracting effects can be accounted for to increase the accuracy of SIFT-MS quantification. This is achieved by relating the currents of ions of various m/z that arrive at the downstream mass spectrometer sampling orifice disc to their count rates at the ion detector after mass analysis. Thus, both diffusion enhancement and mass discrimination are parameterized as a function of m/z and these are combined to provide an overall discrimination factor for the particular analytical instrument. (C) 2001 American Society for Mass Spectrometry.

Abstract: Selected ion-flow tube mass spectrometry, SIFT-MS, relies on chemical ionization of trace gases in air and breath samples using precursor ions that can be rapidly changed to allow the analysis of transient or limited-volume samples. The precursor ion species of choice are H3O+, NO+ and O-2(+) because they do not react with the major components of air. In this article, we present the results of a study designed to investigate if consistent quantification of chemically different compounds can be realized using these three precursor ion species in the presence of humid air and breath. The neutral compounds included in the study are ammonia, dimethylamine, acetone, benzene, isoprene, ethanol, and 1-propanol. These were chosen primarily because the reactions of these compounds with the three precursor ions are representative of the diverse ion chemistry met in SIFT-MS analyses and, in addition, because of their biological and environmental significance, which renders them of particular interest. The results of this study show that consistent quantification can be achieved for all these neutral compounds when the complete ion chemistry involved in the analyses is properly accounted for. It is particularly important to account for the involvement in the ion chemistry of hydrated hydronium ions when using H3O+ precursor ions and for the presence of hydrated product ions produced when very humid samples are being analyzed. This study also indicates that all three precursor ion species are not always suitable for the analysis of particular compounds but that two of the three can always be used. The classes of compound that are best analyzed by each precursor ion species are also indicated. These results indicate the power of SIFT-MS in minimizing ambiguity and improving the accuracy of on-line, direct analysis of the trace gases in humid air and breath. (C) 2001 Elsevier Science B.V.

Abstract: We have assessed the accuracy and precision of our flowing afterglow mass spectrometric method (FA-MS) for absolute measurements of deuterium abundance in water using standardised tap water/D(2)O mixtures within the D/H range from 155 ppm (local tap water) to 1104 ppm, prepared by the gravimetric method. The results of this study show that a precision and accuracy of 1% can be achieved for the deuterium abundance in water samples. This is quite adequate for the main application, which is the rapid, non-invasive measurement of total body water by deuterium analysis of breath water vapour using the D(2)O dilution method.

Abstract: BACKGROUND: Isoprene is the most abundant hydrocarbon present in breath, and recent reports indicate that breath concentrations increase following haemodialysis. The purpose of this study was to establish whether selected ion flow tube mass spectrometry (SIFT-MS), a newly established technique in breath analysis, may be used to quantify breath isoprene in haemodialysis patients in the clinical setting. SIFT-MS is compared and contrasted with the established gas chromatography mass spectrometric technique for this purpose. METHODS: Three consecutive exhalations from 19 haemodialysis patients (12 males, seven females) undergoing a morning dialysis shift were analysed just prior to commencing treatment. Within 5 min of completing their usual dialysis regimen, using polysulphone membranes, the breath of each patient was analysed again. Additional contemporary samples were obtained from 17 normal controls. Breath isoprene was quantified using SIFT-MS, a method previously validated quantitatively using neat isoprene. RESULTS: Successful measurements of breath isoprene were obtained for each subject within 2 min, with minimum disruption to a busy dialysis environment. The coefficient of variation of triplicate measurements of breath isoprene was <10%. Prior to dialysis, the mean (+/-SD) breath isoprene concentration (138+/-63 parts per billion (ppb)) was significantly greater than for normal controls (89+/-36 ppb; P=0.016). Immediately following treatment, breath isoprene increased significantly to 184+/-95 ppb (P=0.023). CONCLUSIONS: SIFT-MS permits the accurate and rapid measurement of breath isoprene in haemodialysis patients in the clinical setting. The previously reported increase in breath isoprene following dialysis treatment is confirmed. SIFT-MS is the ideal analytical tool to investigate this phenomenon further.

Abstract: We have developed a new method for the on-line quantification of deuterium in water vapour. We call this method flowing afterglow mass spectrometry (FA-MS). A swarm of H3O+ precursor ions is created in flowing helium carrier gas by a microwave discharge. These precursor ions react with the H2O, HDO, H2(17)O and H2(18)O molecules in a water vapour sample that is introduced into the carrier gas/H3O+ ion swarm. The hydrated ions, H3O+.(H2O)3 at m/z 73, and their isotopic variant ions H8DO4(+) and H9(17)OO(3)(+) at m/z 74 and H9(18)OO(3)(+) at m/z 75, are thus formed. By adopting the known fractional abundance of 18O in water vapour, and accounting for the contribution of the isotopic ions H9(17)OO(3)(+) to the ion signal at m/z 74, a measurement of the 74/75 ion signal ratio under equilibrium conditions provides the fractional deuterium abundance in the water vapour sample. Using this technique, the deuterium abundance in the water vapour present in single exhalations of breath can be determined. Thus, from the temporal variations of breath deuterium following the ingestion of a known quantity of D(2)O, we show that total body water can be determined non-invasively and the kinetics of water flow around the body can be tracked.

Abstract: We describe how selected ion flow tube mass spectrometry (SIFT-MS) can be used to determine the absolute humidity of air, breath and liquid headspace samples. This involves the determination of the relative count rates of the H3O+ ions and those H3O+.(H2O)(1,2,3) hydrate ions that inevitably form in the helium carrier gas when humid samples are being analysed by SIFT-MS using H3O+ precursor ions. This requires an understanding of the kinetics of hydrated hydronium ion formation, the involvement of mass discrimination in the analytical quadrupole mass spectrometer and the decreased diffusive loss of the heavier hydrates along the flow tube. Thus, we show that the humidity of breath and liquid headspace samples, typically at the few percent level, can be directly obtained on-line to the SIFT-MS instrument along with the concentrations of trace gases, which are present at much lower levels. We emphasise the value of parallel humidity measurements in ensuring good real-time sampling of breath and liquid headspace and the value of such measurements to trace gas analysis using SIFT-MS.

Abstract: We report the results of a study of the reactions of H3O+, NO+ and O-2(+.) ions with H2S. This study was undertaken to provide a thorough understanding of the ion chemistry required for accurate quantification of H2S in humid air by selected ion flow tube mass spectrometry (SIFT-MS), It shows that slow reactions occur between H3S+, the primary product ions of the H3O+/H2S reaction, and the abundant H2O molecules present in humid air and breath. These reactions disturb somewhat the quantification of H2S by this analytical method, but the kinetic data obtained in this study facilitate precise quantification of H2S in humid air. This study also shows that NO+ does not react with H2S, and that O-2(+.) does react rapidly with H2S, but the product H2S+. ions react rapidly with H2O. Thus, NO+ and O-2(+.) cannot he used as precursor ion for analysis of H2S in moist air by SIFT-MS. A sample SIFT mass spectrum is shown from which H2S and several other volatile compounds have been quantified in a sample of cow rumen gas. Copyright (C) 2000 John Wiley & Sons, Ltd.

Abstract: A new method has been developed for the determination of the isotope abundance ratios of deuterium, D, and oxygen-18, O-18, in water vapor (and water) using selected ion flow tube mass spectrometry (SIFT-MS). H3O+ ions are injected into the helium carrier gas where they associate with the H2O and HDO molecules in a sample of water introduced into the carrier gas. The D and O-18 contents of the product cluster ions H8DO4+ and (H9OO3+)-O-18 at m/e = 74 and 75, respectively, are determined by reference to the majority cluster ion H9O4+ at m/e = 73. Allowance is made for the contribution of the (H8OO3+)-O-17 ions to the m/z = 74 ions. Absolute isotopic ratios are measured within seconds without the need for precalibration of the SIFT-MS instrument, currently to an accuracy of better than 2%. (J Am Soc Mass Spectrom 2000, 11, 866-875) (C) 2000 American Society for Mass Spectrometry.

Abstract: The headspaces above faecal and urine samples provided by six pigs have been analysed using selected ion flow tube mass spectrometry (SIFT/MS). The concentrations of ammonia, nitric oxide, nitrogen dioxide, acetone, methanol, ethanol, dimethyl sulphide (DMS) and low molecular weight carboxylic acids in the headspace volume were measured down to the parts per billion (ppb) levels. The differences in the relative concentrations of these compounds between faeces and urine, the implications of these differences and the advantages of using SIFT/MS in such diagnostic and physiological monitoring work are discussed. (C) 2000 Elsevier Science Ltd. All rights reserved.

Abstract:

Abstract: A selected ion how tube (SIFT) experimental investigation has been carried out of the reactions of H3O+ NO+ and O-2(+) with NO, NO2, N2O and HNO2, in order to obtain the essential kinetic data for the analyses of these compounds in air using selected ion flow tube mass spectrometry (SIFT-MS), These investigations show that NO+ ions do not react at a significant rate with any of these NO, compounds and that H3O ions react only with HNO2 (product ions H2NO2+ (75%) and NO+ (25%)), O-2(+) ions react with NO (product ion NO+), NO2 (product ion NO2+) and HNO2 (product ions NO+ (75%), NO; (25%)), but not with N2O, We conclude that both NO and NO2 can be accurately quantified in air using only O-2(+) precursor ions and SIFT-MS when HNO2 is not present. However, when HNO2 is present it invariably co-exists with both NO and NO2 and then both H3O+ and O-2(+) precursor ions are needed to determine the partial pressures of NO, NO2 and HNO2 in the air mixture. We also conclude that currently N2O cannot be analysed in air using SIFT-MS. Copyright (C) 2000 John Wiley & Sons, Ltd.

Abstract: Selected ion flow tube mass spectrometry (SIFT-MS) detects and quantifies in real time the trace gases, M, in air/breath samples introduced directly into a flow tube. Inevitably, relatively large partial pressures of water vapour are introduced with the sample and the water molecules become involved in the ion chemistry on which this analytical technique depends. When H3O+ ions are used as the precursors for chemical ionisation and SIFT mass spectrometric analyses of M, they generally result in the formation of MH+ ions. Also, when water vapour is present the H3O+ ions are partially converted to hydrated hydronium ions, H3O.+(H2O)(1,2,3). The latter may act as precursor ions and produce new product ions like MH.+(H2O)(1,2,3) via ligand switching and association reactions. This ion chemistry and the product ions that result from it must be accounted for in accurate analyses by SIFT-MS. In this paper we describe the results of a detailed SIFT study of the reactions involved in the quantification of acetone, ethyl acetate, diethyl ether, methanol, ethanol, ammonia and methyl cyanide by SIFT-MS in the presence of water vapour, This study was undertaken to provide the essential data that allows more accurate analyses of moist air and breath by SIFT-MS to be achieved. It is shown using our standard analysis procedure that the error of SIFT-MS quantification caused by the presence of water vapour is typically 15%, An improved analysis procedure is then presented that is shown to reduce this error to typically 2%, Additionally, some fundamental data have been obtained on the association reactions of protonated organic molecules, MH+ ions, with water molecules forming MH.+H2O monohydrate ions, For some types of M, reaction sequences occur that lead to the formation of dihydrate and trihydrate ions, Copyright (C) 2000 John Wiley & Sons, Ltd.

Abstract:

Abstract:

Abstract: We report the results of a study of the reactions of H(3)O(+), NO(+) and O(2)(+.) ions with H(2)S. This study was undertaken to provide a thorough understanding of the ion chemistry required for accurate quantification of H(2)S in humid air by selected ion flow tube mass spectrometry (SIFT-MS). It shows that slow reactions occur between H(3)S(+), the primary product ions of the H(3)O(+)/H(2)S reaction, and the abundant H(2)O molecules present in humid air and breath. These reactions disturb somewhat the quantification of H(2)S by this analytical method, but the kinetic data obtained in this study facilitate precise quantification of H(2)S in humid air. This study also shows that NO(+) does not react with H(2)S, and that O(2)(+.) does react rapidly with H(2)S, but the product H(2)S(+.) ions react rapidly with H(2)O. Thus, NO(+) and O(2)(+.) cannot be used as precursor ion for analysis of H(2)S in moist air by SIFT-MS. A sample SIFT mass spectrum is shown from which H(2)S and several other volatile compounds have been quantified in a sample of cow rumen gas.

Abstract: A new method has been developed for the determination of the isotope abundance ratios of deuterium, D, and oxygen-18, 18O, in water vapor (and water) using selected ion flow tube mass spectrometry (SIFT-MS). H3O+ ions are injected into the helium carrier gas where they associate with the H2O and HDO molecules in a sample of water introduced into the carrier gas. The D and 18O contents of the product cluster ions H8DO4+ and H9(18)OO3+ at m/e = 74 and 75, respectively, are determined by reference to the majority cluster ion H9O4+ at m/e = 73. Allowance is made for the contribution of the H8(17)OO3+ ions to the m/z = 74 ions. Absolute isotopic ratios are measured within seconds without the need for precalibration of the SIFT-MS instrument, currently to an accuracy of better than 2%.

Abstract: A selected ion flow tube (SIFT) experimental investigation has been carried out of the reactions of H3O+, NO+ and O2+ with NO, NO2, N2O and HNO2, in order to obtain the essential kinetic data for the analyses of these compounds in air using selected ion flow tube mass spectrometry (SIFT-MS). These investigations show that NO+ ions do not react at a significant rate with any of these NOx compounds and that H3O+ ions react only with HNO2 (product ions H2NO2+ (75%) and NO+ (25%)). O2+ ions react with NO (product ion NO+), NO2 (product ion NO2+) and HNO2 (product ions NO+ (75%), NO2+ (25%)), but not with N2O. We conclude that both NO and NO2 can be accurately quantified in air using only O2+ precursor ions and SIFT-MS when HNO2 is not present. However, when HNO2 is present it invariably co-exists with both NO and NO2 and then both H3O+ and O2+ precursor ions are needed to determine the partial pressures of NO, NO2 and HNO2 in the air mixture. We also conclude that currently N2O cannot be analysed in air using SIFT-MS.

Abstract: Selected ion flow tube mass spectrometry (SIFT-MS) detects and quantifies in real time the trace gases, M, in air/breath samples introduced directly into a flow tube. Inevitably, relatively large partial pressures of water vapour are introduced with the sample and the water molecules become involved in the ion chemistry on which this analytical technique depends. When H(3)O(+) ions are used as the precursors for chemical ionisation and SIFT mass spectrometric analyses of M, they generally result in the formation of MH(+) ions. Also, when water vapour is present the H(3)O(+) ions are partially converted to hydrated hydronium ions, H(3)O(+).(H(2)O)(1,2,3). The latter may act as precursor ions and produce new product ions like MH(+).(H(2)O)(1,2,3) via ligand switching and association reactions. This ion chemistry and the product ions that result from it must be accounted for in accurate analyses by SIFT-MS. In this paper we describe the results of a detailed SIFT study of the reactions involved in the quantification of acetone, ethyl acetate, diethyl ether, methanol, ethanol, ammonia and methyl cyanide by SIFT-MS in the presence of water vapour. This study was undertaken to provide the essential data that allows more accurate analyses of moist air and breath by SIFT-MS to be achieved. It is shown using our standard analysis procedure that the error of SIFT-MS quantification caused by the presence of water vapour is typically 15%. An improved analysis procedure is then presented that is shown to reduce this error to typically 2%. Additionally, some fundamental data have been obtained on the association reactions of protonated organic molecules, MH(+) ions, with water molecules forming MH(+).H(2)O monohydrate ions. For some types of M, reaction sequences occur that lead to the formation of dihydrate and trihydrate ions.

Abstract: We have used selected ion how tube mass spectrometry (SIFT-MS) to determine the concentration of formaldehyde in the headspace of urine from patients suffering from bladder and prostate cancer and from several healthy subjects as controls. We address the potential problems associated with the use of ion chemistry to quantify formaldehyde in the presence of the relatively large number densities of water molecules and show that formaldehyde can be quantified in urine headspace using analysis by SIFT-MS. These studies show that formaldehyde is clearly elevated in the headspace of the urine from the cancer patients as compared with urine from the healthy controls. Thus, with further improvements in the methodology and the sensitivity of our SIFT-MS technique, formaldehyde quantification in urine headspace using this new analytical method could be a valuable non-invasive indicator of the presence of early-stage tumours in the body, Copyright (C) 1999 John Wiley & Sons, Ltd.

Abstract: We describe the results of a selected ion flow tube (SIFT) study of the reactions of H3O+, NO+, and O-2(+) with the monosubstituted halobenzenes, C6H5X, the monosubstituted halotoluene isomers 2-C6H5CH3X and 4-C6H5CH3X (X = F, Cl, Br, I), benzyl chloride, C6H5CH2Cl, benzyl bromide, C6H5CH2Br, and the monosubstituted halomethanes and haloethanes CH3X and C2H5X (X = Cl, Br, I). The H3O+ reactions with the aromatic halocarbons, M, are rapid and mostly proceed via direct proton transfer producing MH+ ions, the exceptions being the benzyl halides in which only HCl (and HBr) elimination occurs from the nascent MH+ ions. The H3O+ reactions with the aliphatic halocarbons are more varied in their rates and products, and in some reactions association occurs forming H3O+. M ions. The NO+ reactions with the aromatics mostly proceed rapidly via charge transfer producing the parent cations M+ only, whereas the NO+ reaction with the aliphatics are generally slow association reactions resulting in NO+. M ions. The O-2(+) reactions are fast mostly proceeding via nondissociative charge transfer producing the parent cations M+ only, but in some of these reactions minority dissociative charge transfer channels are evident in which a halogen atom is eliminated leaving the corresponding hydrocarbon ion. In conclusion, some general observations are made concerning near-thermoneutral charge transfer and proton transfer processes. (Int J Mass Spectrom 189 (1999) 213-223) (C) 1999 Elsevier Science B.V.

Abstract: We have used our selected ion flow tube mass spectrometric method (SIFT-MS) to study isoprene levels in the alveolar breath of 29 healthy volunteers during normal working hours at the varying states of nutrition occurring during this period. Quantification of the breath isoprene was achieved using O-2(+) precursor ions to avoid complications which can arise when using H3O+ precursor ions for isoprene analysis. The present data indicate that the spread of the alveolar isoprene levels in this sample of healthy individuals is 22 to 234 ppb and that the mean value is 83 ppb with a standard deviation of 45 ppb, These levels are compared with those previously determined using other techniques and are seen to be at the low end of the values previously reported. The present studies are a prelude to an investigation of the proposed correlation of breath isoprene levels with psychological, physical and biochemical stress. Copyright (C) 1999 John Wiley & Sons, Ltd.

Abstract: We describe the use of our selected ion Bow tube mass spectrometric technique (SIFT-MS) for the analysis of the headspace above urine. Ammonia, nitric oxide, acetone, ethanol and methanol are identified as the dominant species. As expected, the ammonia is increased in the headspace by making the urine alkaline and the nitric oxide is increased by making the urine acidic. Nitric oxide is abnormally high in the headspace of acidified bacterially infected urine and nitrous acid is also detected. The potential clinical implications of analyses of urine by SIFT-MS are alluded to. Copyright (C) 1999 John Wiley & Sons, Ltd.

Abstract: We describe the results of a selected ion flow tube (SIFT) study of the reactions of H3O+, NO+, and O-2(+), which are the chosen ions for chemical ionisation in our SIFT trace gas analytical method, with eleven structural amine isomers having the molecular formula M = C5H13N. These isomers comprise seven primary, two secondary, and two tertiary amines. The product of the reactions of H3O+ with the primary amines progress from only the parent protonated molecule MH+ for the linear chain 1-pentylamine towards an increasing fraction of NH4+ as the carbon chain becomes more branched, until for the very branched 2-methyl-2-butylamine reaction, NH4+ is the major product (>90%). For the secondary and tertiary amine reactions with H3O+ the major product ion is MH+ in parallel with product ions (M-H)(+) that result from H-2 elimination from MH+, the latter ions being 30% of the product distribution for the tertiary amine, N,N-diethylmethylamine reaction. The NO+ reactions with the primary amines mostly proceed via parallel nondissociative charge transfer (producing Mi ions) and hydride ion transfer [producing (M-H)(+) ions]. With increased branching of the primary amines and for the secondary and tertiary amines, dissociative charge transfer occurs, mainly producing (M-R)(+) ions and various alkyl radicals, R (= CH3, C2H5, C3H7). The O-2(+) reactions with all these amine isomers proceed via dissociative charge transfer, mainly producing (M-R)(+) ions. Comparisons of the products of these O-2(+) reactions with the �cracking patterns� produced by 70 eV electron impact on these amines show remarkable similarities except for one or two of the isomers. (Int J Mass Spectrom 185/186/187 (1999) 139-147) (C) 1999 Elsevier Science B.V.

Abstract: We describe the results of a selected ion flow tube study of the reactions of H3O+, NO+, and O-2(+) with the chloromethanes CH3Cl, CH2Cl2, CHCl3, and CCl4, the chloroethanes CH2ClCH2Cl, CH3CHCl2, CH3CCl3, and CHCl2CHCl2, and the chloroethylenes CHClCCl2 and C2Cl4. The H3O+ reactions with these molecules, M, are mostly rapid but unusually varied, the most evident processes being direct proton transfer producing MH+ ions, ion/molecule association producing H3O+. M ions, HCl elimination from the protonated molecule producing (M-Cl)(+) ions, and even incorporation of H2O into the ion with the elimination of one or two HCl molecules. The NO+ reactions are generally slow and proceed largely via ion/molecule association producing NO+.M ions. Only one of the reactions, that of CH3CCl3, is fast and proceeds via Cl- transfer producing CH3CCl2+: and an NOCl molecule. The O-2(+) reactions are apparently all fast and proceed via charge transfer producing the parent cations M+ and via dissociative charge transfer with the elimination of Cl atoms and HCl molecules. In only one of these O-2(+) reactions (that with CHCl2CHCl2) is the carbon-carbon bond broken. (C) 1999 Elsevier Science B.V.

Abstract: This paper is concerned with the application of our selected ion flow tube mass spectrometric analytical method (SIFT-MS) to the analysis of the complex aromas of some food products. This SIFT/MS chemical ionisation technique, to date mostly applied to breath analysis in medicine and health and safety practice, involves the use of pre-selected H3O+, NO+ and O-2(+) ions to �soft ionise� the volatile organic compounds (VOCs) that constitute complex mixtures such as food aromas. The kinetics involved are well-defined thus allowing quantification of several trace gases simultaneously in an air sample in real time without the need for pre-calibration, In order to facilitate the interpretation of the spectra obtained for complex mixtures by SIFT/MS we have carried out detailed studies of the reactions of these three ion species with a wide variety of organic compounds including many alcohols, aldehydes, ketone, esters and organosulphur compounds. A large kinetics database has thus been created and general patterns of reactivity are seen which are shown to be invaluable for SIFT/MS analyses. Thus, the SIFT mass spectra for some specific food flavours and for the VOCs emitted by cut onion, crushed garlic and ripe banana are presented and interpreted. Finally, the temporal variations in the concentrations of some of the VOCs emitted by these food products, obtained in real time using SIFT/MS in the selected ion monitoring mode, are also presented, which demonstrate the value of this analytical technique in food research. Copyright (C) 1999 John Wiley & Sons, Ltd.

Abstract: We have used our selected ion flow tube mass spectrometric method (SIFT-MS) to study isoprene levels in the alveolar breath of 29 healthy volunteers during normal working hours at the varying states of nutrition occurring during this period. Quantification of the breath isoprene was achieved using O(2)(+) precursor ions to avoid complications which can arise when using H(3)O(+) precursor ions for isoprene analysis. The present data indicate that the spread of the alveolar isoprene levels in this sample of healthy individuals is 22 to 234 ppb and that the mean value is 83 ppb with a standard deviation of 45 ppb. These levels are compared with those previously determined using other techniques and are seen to be at the low end of the values previously reported. The present studies are a prelude to an investigation of the proposed correlation of breath isoprene levels with psychological, physical and biochemical stress.

Abstract: The rate coefficients and product ion branching ratios have been determined for reactions between NO+ and three ketones, acetone, 2-butanone, and 3-pentanone, as a function of NO+/reactant ketone centre-of-mass energy, E-r, and NO+/helium carrier gas atom centre-of-mass energy, E-c, in a flowing afterglow selected ion flow drift tube apparatus. In these experiments, the helium carrier gas was maintained at a temperature of 300 K. At zero drift field, association was the dominant channel occurring at close to the collision rate forming NO.(+) ketone adduct ions. At higher drift fields (E-r, E-c < 1 eV), charge transfer and dissociative charge transfer channels became the major channels forming fragment ions of the ketones. The decrease in the association rate coefficient with increasing E-c exhibits an inverse power law dependence k(3) proportional to E-c(-n) where n similar to 2.5 for all three ketones. This dependence is much larger than predicted by simple theory and may be indicative of low energy vibrations contributing to the total energy pool in the (NO. ketone)(+*) excited complex. (Int J Mass Spectrom 193 (1999) 35-43) (C) 1999 Elsevier Science B.V.

Abstract: We have used selected ion flow tube mass spectrometry (SIFT-MS) to determine the concentration of formaldehyde in the headspace of urine from patients suffering from bladder and prostate cancer and from several healthy subjects as controls. We address the potential problems associated with the use of ion chemistry to quantify formaldehyde in the presence of the relatively large number densities of water molecules and show that formaldehyde can be quantified in urine headspace using analysis by SIFT-MS. These studies show that formaldehyde is clearly elevated in the headspace of the urine from the cancer patients as compared with urine from the healthy controls. Thus, with further improvements in the methodology and the sensitivity of our SIFT-MS technique, formaldehyde quantification in urine headspace using this new analytical method could be a valuable non-invasive indicator of the presence of early-stage tumours in the body.

Abstract: The selected ion flow tube technique was used to quantify in breath the trace gases acetone, ammonia, ethanol, isoprene, and methanol during single exhalations while fasting and in response to feeding. Six normal volunteers were fasted for 12 h, and, after baseline breath samples were obtained, were fed a liquid protein-calorie meal to provide 0.47 g/kg of protein (Fortisip). Further breath samples were obtained at 20, 40, and 60 min, and then hourly for a further 5 h. Breath acetone concentrations fell from a maximum during fasting, reaching their nadir between 4 and 5 h. Breath ammonia concentrations fell immediately to one-half their fasting levels before a steady increase to two or three times baseline values at 5 h. There was a brief increase in breath ethanol concentrations after feeding, reflecting detectable ethanol contamination of the food. Subsequently, breath ethanol levels remained low throughout the experimental protocol. Isoprene concentrations did not change significantly, whereas changes in methanol concentrations reflected those in the ambient air. This preliminary study indicates that the selected ion flow tube technique may be used to detect changes in the trace gases present in breath and define their concentrations in the fasting and replete state. Of particular interest is the biphasic response of the breath ammonia concentration after feeding.

Abstract: We describe the use of our selected ion flow tube mass spectrometric technique (SIFT-MS) for the analysis of the headspace above urine. Ammonia, nitric oxide, acetone, ethanol and methanol are identified as the dominant species. As expected, the ammonia is increased in the headspace by making the urine alkaline and the nitric oxide is increased by making the urine acidic. Nitric oxide is abnormally high in the headspace of acidified bacterially infected urine and nitrous acid is also detected. The potential clinical implications of analyses of urine by SIFT-MS are alluded to.

Abstract: The selected ion flow tube technique was used to quantify in breath the trace gases acetone, ammonia, ethanol, isoprene, and methanol during single exhalations while fasting and in response to feeding. Six normal volunteers were fasted for 12 h, and, after baseline breath samples were obtained, were fed a liquid protein-calorie meal to provide 0.47 g/kg of protein (Fortisip). Further breath samples were obtained at 20, 40, and 60 min, and then hourly for a further 5 h. Breath acetone concentrations fell fi om a maximum during fasting, reaching their nadir between 4 and 5 h. Breath ammonia concentrations fell immediately to one-half their fasting levels before a steady increase to two or three times baseline values at 5 h. There was a brief increase in breath ethanol concentrations after feeding, reflecting detectable ethanol contamination of the food. Subsequently, breath ethanol levels remained low throughout the experimental protocol. Isoprene concentrations did not change significantly, whereas changes in methanol concentrations reflected those in the ambient air. This preliminary study indicates that the selected ion flow tube technique may be used to detect changes in the trace gases present in breath and define their concentrations in the fasting and replete state. Of particular interest is the biphasic response of the breath ammonia concentration after feeding.

Abstract: We report the results of a selected ion flow tube study at 300 K of the reactions of H3O+, NO+, and O-2(+) with ammonia, five primary, three secondary, and two tertiary amines, pyrrole and pyridine, and acetonitrile and benzonitrile. The major product ions of all the H3O+ reactions are the protonated parent molecules, MH+, these being the single product in six of these reactions; NH4+ is seen to be a minor product of three of the primary amine reactions, and ions of the type (M-H)(+) are minor products of the secondary and tertiary amine reactions. The low ionisation energies of all the amines, pyrrole, and pyridine ensures that charge transfer occurs in their reactions with NO+, this generally being sufficiently exothermic to result in partial fragmentation of the (M+)* nascent product ions resulting in (M-H)(+) and (M-CH3)(+) ions. However, charge transfer is endothermic between NO+ and pyridine and the two nitriles and then ion-molecule association occurs, producing the adduct ions NO+. M. The reactions of the more energetic O-2(+) ions with all the amines proceed via dissociative charge transfer, producing major products ions of the type (M-R)(+), where R is the alkyl radicals, CH3, C2H5, etc., as appropriate, but the parent cations, M+, are the single product ions for the reactions of the more stable aniline, pyrrole, pyridine, and benzonitrile. (C) 1998 Elsevier Science B.V.

Abstract: We show how our selected ion Bow tube mass spectrometric technique for trace gas analysis can be used to determine the concentrations of ammonia in alveolar breath from single exhalations using both H3O+ and O-2(+) precursor ions for chemical ionization. Thus, data are presented of the alveolar ammonia concentrations in the breath of six healthy volunteers following the ingestion of a liquid protein meal, which show that consistent values are obtained using these two precursor ions. Alveolar breath ammonia concentrations (which range from 200 to 1750 ppb in these individuals) are compared with those obtained from bag samples of breath from the same individuals. (C) 1998 John Wiley & Sons, Ltd.

Abstract: We report the results of a selected ion flow tube (SIFT) study of the reactions of H3O+ NO+ and O-2(+) with eight organosulphur molecules, M. If we assume that all the exothermic proton transfer reactions of H(3)O(+)occur at the collision rate (i.e. the rate coefficients, k, are equal to the collisional rate coefficient, k(c)), it is seen that the k for most of the NO+ and O-2(+) reactions also are equal to or close to k(c). However, the reaction of H3O+ with one of the chosen reactants, CS2, is known from our previous SIFT study to be slightly endothermic, and therefore it proceeds more slowly than the collisional rate. The ionic product of seven of the H3O+ reactions is only the protonated parent molecule MH+, but in one reaction, that of thiolacetic acid CH3COSH, elimination of an H2S molecule occurs in a fraction of the collisions. The NO+ reactions mostly proceed via charge transfer, producing the parent molecular ion M+, but the reaction with ethanthiol is unusually complicated, with four processes occurring in parallel (charge transfer, H- and SH- transfer, and ion-molecule association), and the reaction with thiolacetic acid occurs exclusively and rapidly via SH- transfer. The O-2(+) reactions proceed by dissociative charge transfer, often with the production of three or more ionic fragments of the parent molecular ion. Sample mass spectra obtained using our SIFT method of analysis of the vapours emitted by cut onion and crushed garlic are presented and discussed, noting the presence of some organosulphur molecules and other organic species. (C) 1998 Elsevier Science B.V.

Abstract: We report the results of a selected ion flow tube (SIFT) study of the reactions of H3O+, NO+ and O-2(+) with some nine carboxylic acids and eight esters. We assume that all the exothermic proton transfer reactions of H3O+ with all the acid and esters molecules occur at the collisional rate, i.e. the rate coefficients, k, are equal to k(c); then it is seen that k values for most of the NO+ and O-2(+) reactions also are equal to or close to k(c). The major ionic products of the H3O+ reactions with both the acids and esters are the protonated parent molecules, MH+, but minor channels are also evident, these being the result of H2O elimination from the excited (MH+)* in some of the acid reactions and an alcohol molecule elimination (CH3OH or C2H5OH) in some of the ester reactions. The NO+ reactions with the acids and esters result in both ion-molecule association producing NO+.M in parallel with hydroxide ion (OH-) transfer with some of the acids, and parallel methoxide ion (CH3O-) and ethoxide ion (C2H5O-) transfer as appropriate with some of the esters. The O-2(+) reactions proceed by dissociative charge transfer with the production of two or more ionic fragments of the parent molecules, the different isomeric forms of both the acid and the ester molecules resulting in different product ions. (C) 1998 Elsevier Science B.V.

Abstract: We report the results of a selected ion flow tube (SIFT) study of the reactions of H3O+, NO+ and O-2(+) with some 10 ethers, M. We assume that all the exothermic proton transfer reactions of H3O+ with all the ether molecules occur at the collision rate, i.e. the rate coefficients, k, are equal to k(c), then it is seen that the k for most of the NO+ and O-2(+) reactions also are equal to or close to k(c). The major ionic products of the H3O+ reactions are unusually complicated compared to the reactions of these reactant ions with many ketones, alcohols, aldehydes and carboxylic acids in which the products are predominantly MH+ and (M-H2O)(+) ions (water molecule elimination). In these ether reactions, water elimination is not observed, but rather MH+ and ions resulting from the elimination of alcohol and hydrocarbon molecules are the common products. The NO-reactions mostly proceed via hydride ion (H-) transfer producing (M-H)(+) ions and an HNO molecule, with parallel alkyl radical ion, R-, abstraction (producing (M-R)(+) ions (and RNO molecules) bring evident in two of the reactions and aikoxide ion, RO-, abstraction (producing hydrocarbon ions and RONO molecules) in two of the other reactions. The NO+/anisole reaction proceeds exclusively via charge transfer, this being allowed because of the low ionization energy of anisole. The O-2(+) reactions proceed by dissociative charge transfer with the production of two or more ionic fragments of the parent molecular ion, the different isomeric forms of these ether molecules resulting in different product ions. (C) 1998 Elsevier Science B.V.

Abstract: We describe the results of a selected ion flow tube study of the reactions of H3O+, NO+, and O-2(+) with the 10 aromatic hydrocarbons benzene, toluene, 1,2-, 1,3-, and 1,4-dimethylbenzene, ethylbenzene, propylbenzene, 1,2,3-, 1,2,3-, and 1,3,5-trimethylbenzene, and 11 aliphatic hydrocarbons which are the alkanes A-butane and 2-methyl propane, n-pentane and 2-methyl butane, n-hexane, n-octane, n-decane and n-dodecane, the alkenes 1-pentene and 2-methyl-2-butene, and the dialkene 2-methyl butadiene (isoprene). All 30 reactions of the aromatic hydrocarbons are fast, the rate coefficients k being close to their respective collisional rate coefficients k(c). The H3O+ reactions all proceed by proton transfer producing the protonated parent molecules MH+, the NO+ reactions proceed largely via nondissociative charge transfer producing M+ ions, and the O-2(+) reactions proceed via charge transfer which is partially dissociative in most cases producing M+ and (M-CH3)+ ions. The k for the 33 aliphatic hydrocarbon reactions are much more varied, ranging from the immeasurable to k(c). Proton transfer is endothermic in the reactions of H3O+ with the smaller hydrocarbons whilst for the larger hydrocarbons reactions ion-molecule association occurs producing H3O+.M ions. The NO+ reactions proceed largely via hydride ion transfer producing (M-H)(+) ions, although partial incorporation of the NO+ into thr. larger hydrocarbons with subsequent fragmentation occurs producing minority ions like RHNO+ (where R are radicals like C3H7, C4H9, etc). The O-2(+) reactions all proceed by rapid dissociative charge transfer, the number of fragment ions increasing with the atomicity of the aliphatic hydrocarbon. (Int J Mass Spectrom 181 (1998) 1-10) (C) 1998 Elsevier Science B.V.

Abstract: We show how our selected ion flow tube mass spectrometric technique for trace gas analysis can be used to determine the concentrations of ammonia in alveolar breath from single exhalations using both H30+ and 02+ precursor ions for chemical ionization. Thus, data are presented of the alveolar ammonia concentrations in the breath of six healthy volunteers following the ingestion of a liquid protein meal, which show that consistent values are obtained using these two precursor ions. Alveolar breath ammonia concentrations (which range from 200 to 1750 ppb in these individuals) are compared with those obtained from bag samples of breath from the same individuals.

Abstract: Various electron attachment processes are reviewed, emphasising the way in which the rates and products of some selected reactions vary with the attaching gas temperature Tbt the temperature, T-e, and the energy of the attaching electrons. The examples illustrating the variety of reactions are the efficient dissociative attachment reaction to CCl4, attachment to SF6 which involves both dissociative and non-dissociative attachment, attachment to CHCl3 which requires activation energy, and attachment to CCl3Br which results in both Cl- and Br- product ions. A model has been presented which is able to quantitatively explain the difference influences of T-g and T-e on the rates of some of these reactions. Also described are the unusually efficient attachment properties of the fullerene molecules C-60 and C-70 as revealed by our FALP experiments, noting that these molecules have potential importance as efficient suppressers of electrical breakdown through gases such as those used to insulate high voltage devices. We emphasise throughout this paper the importance of an understanding of the separate influences of gas and electron temperature on attachment reactions for the modelling of practical gas discharge media such as etchant plasmas.

Abstract: The selected ion flow tube (SIFT) is a technique originally developed for the determination of rate coefficients for gas phase reactions. Recently the SIFT has been applied to the detection of trace gases in air and breath. The SIFT method is capable of determining absolute partial pressures of trace gases in air without the need for calibration. However, it is necessary to show that SIFT determinations are of acceptable accuracy. This study reports the findings of a validation study in which eight trace gases in air, in the concentration range of 100 ppb-30 ppm, were simultaneously detected and quantified. In addition, the results of the measurement of the partial pressure of perchloroethylene (C2Cl4) On the breath of a volunteer some 16 h after a controlled exposure art reported. This study demonstrates that several gases in breath can be rapidly quantified from just a single exhalation. Crown copyright (C) 1997 Published by Elsevier Science Ltd.

Abstract: The reactions of CO+, CO2+, SO2+, NO2+, CS2+, CN+, C2N2+, and C2H3+ with H atoms and H-2 molecules have been studied in a selected ion dow tube operated at (300+/-5) K. The H atom reactions proceed variously by the processes of atom exchange and charge transfer (when allowed), none proceed at the Langevin rate, and the rates of several of them appear to be influenced by the spin states of the product species. Most of the H-2 reactions proceed by H atom abstraction and at a large fraction of the Langevin rate. (C) 1997 American Institute of Physics.

Abstract:

Abstract: The results are reported of a selected ion flow tube (SIFT) study of the rate coefficients and the ionic products of the reactions of H3O+, NO+ and O-2(+) with some 11 aldehydes and nine ketones including the structural isomers of some. We assume that the 20 exothermic H3O+ proton transfer reactions proceed at the collisional rate and on this basis the large majority of the remaining 40 reactions included in this study also proceed close to the collisional rate. A variety of reaction processes are seen to occur. The H3O+ reactions proceed via proton transfer which for the ketones produces the protonated molecules only but which in the aldehyde reactions H,O elimination from the protonated molecule also occurs. The NO+ reactions with the aldehydes proceed largely via the process of hydride ion transfer whereas ion-molecule association is the dominant process in the NO+/ketone reactions with charge transfer also evident in some cases. The O-2(+) reactions with both the aldehydes and ketones proceed largely via charge transfer which in all reactions is partially dissociative producing several ionic products for the more polyatomic reactant molecules. Different products are observed in the reactions of O-2(+) with some of the structural isomers. (C) 1997 Elsevier Science B.V.

Abstract: We report the results of a selected ion flow tube (SIFT) study of the reactions of H3O+, NO+ and O-2(+) with some 17 alcohols ranging in complexity from methanol to octanol and menthol, and including some structural isomers. This study was carried out in order to extend the database (i.e. rate coefficients and product ions of appropriate ion/molecule reactions) required for the SIFT method of trace gas analysis which utilises the aforementioned ions for chemical ionisation. The H3O+ reactions proceed via exothermic proton transfer, which we assume to proceed at the collisional rate. Thus all of the 51 reactions (except two) occur at or close to the collisional rate. Only in a minority of these proton transfer reactions is the protonated parent molecule the single ion product; rather it is seen that the protonation of most of these alcohols by H3O+ is followed by the ejection of an H2O molecule from the excited product ion thus leaving the appropriate hydrocarbon ion. The NO+ reactions proceed largely via the processes of hydride ion transfer producing the appropriate carboxy ion (and HNO), and hydroxide ion transfer producing the appropriate hydrocarbon ion (and HNO2). The Of reactions proceed via charge transfer, the large majority of the reactions resulting in mere than one product ion, which are mostly hydrocarbon fragment ions but in a few cases carboxy ions are formed. The product ions for the reactions of the various structural isomers are sometimes different, and this offers a way of distinguishing between the isomeric forms of some alcohols. (C) 1997 Elsevier Science B.V.

Abstract: Dissociative electron attachment to CCl3Br has been studied using a flowing afterglow/Langmuir probe (FALP) and a crossed beam technique. In the FALP experiment the overall attachment rate coefficients and the branching ratio into the Cl- and the Br- product channels, R = Cl-/(Cl- + Br-), were measured as a function of the gas temperature, T-g, in the range of 300-540K and the electron temperatures, T-e, from T-g to 4000K indicating that R approached the statistical value of 0.75 at the highest T-g. At T-g = 540K both Cl-2(-) and ClBr- molecular ions were observed at about the 2% level. An apparent activation energy of 55 meV for the overall attachment reaction was derived using a model developed previously to describe the dependence of dissociative electron attachment rates on T-g and T-e. The crossed beam experiment provided relative attachment cross-sections for the production of Cl- and Br-as a function of electron energy, E, from near zero up to similar to 2 eV at several T-g within the range 311-423 K. The absolute cross-sections at T-g = 311K were obtained from the FALP value using a calibration procedure. At low E the overall attachment cross-section varies as E-L in accordance with s-wave capture theory. In accordance with the FALP data R increases from 0.2 at low E and the lowest T-g to the statistical value of 0.75 at high E and high T-g. A peak observed in the cross-section at an E of about 0.7 eV is tentatively attributed to p-wave electron attachment. The rapid decrease of this peak cross-section with T-g is ascribed to autodetachment. Published by Elsevier Science B.V.

Abstract:

Abstract: We present an overview of the development and use of our selected-ion flow tube (SIFT) technique as a sensitive, quantitative method for the rapid, real-time analysis of the trace gas content of atmospheric air and human breath, presenting some pilot data from various research areas in which this method will find valuable applicationl. We show that it is capable of detecting and quantifying trace gases, in complex mixtures such as breath, which are present at partial pressures down to about 10 parts per billion. Following discussions of the principles involved in this SIFT method of analysis, of the experiments which we have carried out to establish its quantitative validity, and of the air and breath sampling techniques involved, we present sample data on the detection and quantification of trace gases on the breath of healthy people and of patients suffering from renal failure and diabetes. We also show how breath ammonia can be accurately quantified from a single breath exhalation and used as an indicator of the presence in the stomach of the bacterium Helicobacter pylori. Health and safety applications are exemplified by analyses of the gases of cigarette smoke and on the breath of smokers. The value of this analytical method in environmental science is demonstrated by the analyses of petrol vapour, car exhaust emissions and the trace organic vapours detected in town air near a busy road. Final examples of the value of this analytical method are the detection and quantification of the gases emitted from crushed garlic and from breath following the chewing of a mint, which demonstrate its potential in food and flavour research. Throughout the paper we stress the advantages of this SIFT method compared to conventional mass spectrometry for trace gas analysis of complex mixtures, emphasizing its selectivity, sensitivity and real-time analysis capability. Finally, we note that whilst the current SIFT is strictly laboratory based, both transportable and portable instruments are under construction and development. These instruments will surely extend the application of this analytical technique into more areas and allow greater exploitation of their on-line and real-time features.

Abstract: Our major objective in this paper is to describe a new method we have developed for the analysis of trace gases at partial pressures down to the ppb level in atmospheric air, with special emphasis on the detection and quantification of trace gases on human breath. It involves the use of our selected ion flow tube (SIFT) technique which we previously developed and used extensively for the study of gas phase ionic reactions occurring in ionized media such as the terrestrial atmosphere and interstellar gas clouds. Before discussing this analytical technique we describe the results of our very recent SIFT and flowing afterglow (FA) studies of the reactions of the H3O+ and OH- ions, of their hydrates H3O+(H2O)(1,2,3) and OH-(H2O)(1,2), and of NO+ and O-2(+), with several hydrocarbons and oxygen-bearing organic molecules, studies that are very relevant to our trace gas analytical studies. Then follows a detailed discussion of the application of our SIFT technique to trace gas analysis, after which we present some results obtained for the analyses of laboratory air, the breath of a healthy non-smoking person, the breath of a person who regularly smokes cigarettes, the complex vapours emitted by banana and onion, and the molecules present in a butane/air flame. We show how the quantitative analysis of breath can be achieved from only a single exhalation and in real time (the time response of the instrument is only about 20 ms). We also show how the time variation of breath gases over long time periods can be followed, using the decay of ethanol on the breath after the ingestion of distilled liquor as an example, yet simultaneously following several other trace gases including acetone and isoprene which are very easily detected on the breath of all individuals because of their relatively high partial pressures (typically 100 to 1000 ppb). The breath of a smoker is richer in complex molecules, some nitrogen containing organics apparently being very evident at the 5 to 50 ppb level. These results and those for banana and onion vapours and butane/air flame forcibly demonstrate the value and the scope of our SIFT ion chemistry approach to the analysis of very complex gas mixtures, and that this method is accurately quantitative if the appropriate ion chemistry is properly understood.

Abstract: We describe the use of our selected ion flow tube (SIFT) technique for the rapid detection and quantification of trace gases in atmospheric air, with special reference to the analysis of human breath. It is based on the chemical ionization of the breath trace gases to the exclusion of the major breath gases, using 'soft' proton transfer from H3O+ ions. Breath samples can either be introduced into the SIFT from bags or by direct breathing into the apparatus, the advantage of the latter approach being that surface active gases such as ammonia and many organic vapours which adsorb onto bag surfaces can be more accurately quantified. We present examples of the analysis of laboratory air, the breath of a non-smoker and of a smoker taken from bag samples, and illustrate the rapid time response of the technique by showing the time profile of acetone on breath during direct breathing into the apparatus. The current partial pressure sensitivity of our SIFT method is within the range 30 ppb to in excess of 100 ppm, but with further development the device could be made more sensitive, 1 ppb being well within reach. A transportable SIFT device is under development which will have applications in environmental, medical and biological research, health and safety monitoring, and in clinical diagnosis.

Abstract: A study of the ion-ion recombination reactions of NO+ with Cl- and I- has been carried out using our flowing afteglow/Langmuir probe (FALP) apparatus at 300 K. These recombination reactions proceed by the transfer of an electron from the I- and Cl- ions to the NO+ ions producing neutral, electronically excited NO molecules and ground state halogen atoms. For ground state reactant ions, only the two lowest electronic states of NO, i.e. the A (2) Sigma(+) and the B (2) Pi(r) states can be generated. This FALP study shows that only NO gamma-bands are emitted by the thermalised NO+/Cl- plasma whereas both NO gamma-bands and NO beta-bands are emitted by the thermalised NO+/I- plasma. From these observations together with our measured values of the recombination coefficients for the reactions, and from a consideration of the reaction energetics, we conclude that electron transfer from both Cl- and I- to NO+ most probably occurs at short distances on the repulsive potential wall and not at longer distances as is usually assumed for this type of reaction.

Abstract: A study has ben carried out using out selected ion flow tube apparatus of the reactions of NO2+ and O-2(+) ions in their vibronic ground states with ten organic species: the hydrocarbons, benzene, toluene, isoprene, cyclopropane, cyclopropane, and n-pentane; the oxygen-containing organics, methanol, ethanol, acetaldehyde, acetone, and diethyl ether. The major objectives of this work are, on the one hand, to fully understand the processes involved in these reactions and, on the other hand, to explore the potential of NO2+ and O-2(+) as chemical ionization agents for the analysis of trace gases in air and on human breath. Amongst the NO2+ reactions, charge transfer, hydride-ion transfer, and termolecular association occur, and the measured rate coefficients, k, for the reactions vary from immeasurably small to the maximum value, collisional rate coefficient, k(c). The O-2(+) reactions are all fast, in each case the k being equal to or an appreciable fraction of k(c), and charge transfer producing the parent organic ion or dissociative charge transfer resulting in two or three fragments of the parent ion are the reaction processes that occur. We conclude from these studies, and from previous studies, that NO2+ ions and O-2(+) ions can be used to great effect as chemical ionization agents for trace gas analysis, especially in combination with H3O+ ions which we now routinely use for this purpose.

Abstract: We describe the use of our selected ion flow tube (SIFT) technique for the rapid detection and quantification of trace gases in atmospheric air, with special reference to the analysis of human breath. It is based on the chemical ionization of the breath trace gases to the exclusion of the major breath gases, using �soft� proton transfer from H3O+ ions. Breath samples can either be introduced into the SIFT from bags or by direct breathing into the apparatus, the advantage of the latter approach being that surface active gases such as ammonia and many organic vapours which adsorb onto bag surfaces can be more accurately quantified. We present examples of the analysis of laboratory air, the breath of a non-smoker and of a smoker taken from bag samples, and illustrate the rapid time response of the technique by showing the time profile of acetone on breath during direct breathing into the apparatus. The current partial pressure sensitivity of our SIFT method is within the range 30 ppb to in excess of 100 ppm, but with further development the device could be made more sensitive, 1 ppb being well within reach. A transportable SIFT device is under development which will have applications in environmental, medical and biological research, health and safety monitoring, and in clinical diagnosis. Crown copyright (C) 1996 Published by Elsevier Science Ltd.

Abstract: We present an overview of the development and use of our selected-ion flow tube (SIFT) technique as a sensitive, quantitative method for the rapid, real-time analysis of the trace gas content of atmospheric air and human breath, presenting some pilot data from various research areas in which this method will find valuable application. We show that it is capable of detecting and quantifying trace gases, in complex mixtures such as breath, which are present at partial pressures down to about 10 parts per billion. Following discussions of the principles involved in this SIFT method of analysis, of the experiments which we have carried out to establish its quantitative validity, and of the air and breath sampling techniques involved, we present sample data on the detection and quantification of trace gases on the breath of healthy people and of patients suffering from renal failure and diabetes. We also show how breath ammonia can be accurately quantified from a single breath exhalation and used as an indicator of the presence in the stomach of the bacterium Helicobacter pylori. Health and safety applications are exemplified by analyses of the gases of the gases of cigarette smoke and on the breath of smokers. The value of this analytical method in environmental science is demonstrated by the analyses of petrol vapour, car exhaust emissions and the trace organic vapours detected in town air near a busy road. Final examples of the value of this analytical method are the detection and quantification of the gases emitted from crushed garlic and from breath following the chewing of a mint, which demonstrate its potential in food and flavour research. Throughout the paper we stress the advantages of this SIFT method compared to conventional mass spectrometry for trace gas analysis of complex mixtures, emphasizing its selectivity, sensitivity and real-time analysis capability. Finally, we note that whilst the current SIFT is strictly laboratory based, both transportable and portable instruments are under construction and development. These instruments will surely extend the application of this analytical technique into more areas and allow greater exploitation of their on-line and real-time features.

Abstract:

Abstract: The selected ion flow tube (SIFT) technique for trace gas analysis of air and breath is based on soft chemical ionisation of the trace gases to the exclusion of the major air and breath gases, in fast-flowing inert carrier gas, exploiting the ion-molecule reactions that occur between the trace gases and the pre selected precursor ions (H3O+, NO+ and O-2(+). The physics and ion chemistry involved in the SIFT technique are described, as are the kinetics of the ion-molecule reactions that are exploited to quantitatively analyse the trace gases. Fast on-line data-acquisition hardware and software have been developed to analyse the mass spectra obtained, from which partial pressures of the trace gases down to about 10 parts per billion can be measured. The time response of the instrument is 20 ms, allowing the profiles of the trace gas concentrations on breath to be obtained during a normal breathing cycle. Pilot results obtained with this SIFT technique include detection and quantification of the most abundant breath trace gases, analysis of cigarette smoke, detection of gases present on smokers� breath and accurate measurement of the partial pressures of NH3, NO and NO2 in air. The simultaneous analysis of several breath trace gases during a single exhalation is clearly demonstrated, and thus different elution times for isoprene and methanol along the respiratory tract are observed. This technique has great potential in many clinical and biological disciplines, and in health and safety monitoring.

Abstract: The selected ion flow tube (SIFT) technique for trace gas analysis of air and breath is based on soft chemical ionisation of the trace gases to the exclusion of the major air and breath gases, in fast-flowing inert carrier gas, exploiting the ion-molecule reactions that occur between the trace gases and the pre selected precursor ions (H3O+, NO+ and O2+). The physics and ion chemistry involved in the SIFT technique are described, as are the kinetics of the ion-molecule reactions that are exploited to quantitatively analyse the trace gases. Fast on-line data-acquisition hardware and software have been developed to analyse the mass spectra obtained, from which partial pressures of the trace gases down to about 10 parts per billion can be measured. The time response of the instrument is 20 ms, allowing the profiles of the trace gas concentrations on breath to be obtained during a normal breathing cycle. Pilot results obtained with this SIFT technique include detection and quantification of the most abundant breath trace gases, analysis of cigarette smoke, detection of gases present on smokers' breath and accurate measurement of the partial pressures of NH3, NO and NO2 in air. The simultaneous analysis of several breath trace gases during a single exhalation is clearly demonstrated, and thus different elution times for isoprene and methanol along the respiratory tract are observed. This technique has great potential in many clinical and biological disciplines, and in health and safety monitoring.

Abstract: The fullerene molecule C-60 is known to attach several electrons in the solid phase, but only recently has it been recognized that it can also attach electrons in the gas phase. The first electron-molecular beam results showed that C-60 and C-70 molecules non-dissociatively attached a single electron over the unusually wide electron energy range from near thermal to about 10 eV, but these studies were not able to provide either the magnitude of the cross sections or describe the low-energy attachment behaviour. But using our flowing afterglow-Langmuir probe (FALP) apparatus we have been able to determine the absolute attachment rate coefficients for both C-60 and C-70 over the electron temperature range 300-4500 K. These FALP experiments have shown that attachment to C-60 at low electron energies (< 1 eV) proceeds predominantly by p-wave electron capture, and that a centrifugal barrier of 0.26 eV is evident which was corroborated by subsequent theory. A similar situation is observed for attachment to C-70 except that for this fullerene molecule there is evidence that at very low electron energies (< 0.05 eV) inefficient s-wave capture may also occur. These FALP data further indicate that at energies above about 0.3 eV extraordinarily efficient electron attachment occurs to both C-60 and C-70, and when the mean thermal cross sections derived from these FALP data are used to normalize the crossed electron-molecular beam data at the common low energies accessible in both experiments, it is clear that electron attachment to these fullerene molecules is very efficient over a wide electron energy range from about 0.3-10 eV above which electron thermionic emission occurs from the hot C-60(-) and C-70(-) nascent negative ions.

Abstract: The current/voltage characteristics of a cylindrical Langmuir probe have been studied in Ar+/electron afterglow plasmas in helium carrier gas under truly thermal conditions at 300 K using our flowing afterglow/Langmuir probe (FALP) apparatus. The orbital motion limited (oml) ion and electron current regions of the probe characteristics have been explored over a wide range of the reduced probe voltage (up to similar to 100) and over a wide range of electron (n(e)) and ion (n(+)) number densities (1.6 x 10(7) to 1.5 x 10(10) cm(-3)) at a constant pressure of the He carrier gas of 1.2 Torr. The observed increase of the probe ion currents above those predicted by collisionless oml theory, resulting in an apparent increase of the measured ion number density above n(e) in the plasma, is explained by the enhancement in the ion current collection efficiency due to collisions of ions with neutral gas atoms in the space charge sheath surrounding the probe. The continuous change in the exponent, x, of the power-law dependence, i(+) proportional to V-p(kappa), of the ion current, i(+), on the probe voltage, V-p, from 0.5 at the highest n(+) (smallest sheath) towards 1.0 at the lowest n(+) (large sheath) indicates that the ion current collection from the plasma changes from the oml current regime at the high n(+), to the continuum regime at the low n(+) when the ions undergo multiple collisions with the helium atoms in the space charge sheath and thus ��drift� towards the probe.

Abstract:

Abstract: A brief review of the recent studies at low energies and low temperatures of two important plasma reaction processes, namely electron attachment and positive ion-electron dissociative recombination, is presented. There are two distinct attachment processes-direct attachment in which the parent negative ion of the reactant molecule is formed and dissociative attachment in which a negative ion and a neutral fragment result. The direct attachment process is exemplified by SF6- production, and special attention is given to the very interesting case of direct electron attachment to the fullerene molecule C-60 which is seen to be a very efficient electron scavenger over a very wide electron energy range. Only dissociative recombination is considered in the paper, and it is indicated that this is usually a very important ionization loss process in a plasma. The rates of dissociative recombination reactions increase with the complexity of the recombining ions, being very high for polyatomic (cluster) ions. The difficult problem of determining the neutral products of dissociative recombination reactions and the attempts that have been made to determine them for some such reactions are briefly referred to.

Abstract: The reactions of the cyclic molecules C6H6 (benzene), c-C3H6 (cyclopropane) and c-C6H12 (cyclohexane) with ArH+ (ArD+), H3+, N2H+, CH5+, HCO+, OCSH+, C2H3+, CS2H+ and H3O+ have been studied at 300 K using a SIFT apparatus. All the reactions except those of C2H3+ proceed via proton transfer and all are fast except the H3O+ and CS2H+ reactions with c-C6H12 which are endothermic and which establish that the proton affinity of c-C6-H12 is 160 +/- 1 kcal mol-1, which is considerably lower than the published value. In the c-C3H6 and the c-C6H12 reactions multiple products are observed and hence ��breakdown curves� for the protonated molecules are constructed and the appearance energies of the various ion products are consistent with available thermochemical data. The reactions of C2H3+ with these cyclic molecules are atypical within this series of reactions in that they appear to proceed largely via hydride ion transfer. The implications of the results of this study to interstellar chemistry are alluded to.

Abstract: The rate coefficients, beta, for the attachment reactions of electrons with CCl4, CHCl3, SF6 and C7F14 have been measured in a Rowing afterglow/Langmuir probe (FALP) apparatus within the range of electron temperature, T-c, from 300 to about 4000 K at a carrier gas temperature, T-g, of 300 K and for the SF6 reaction additionally at a T-g of 540 K. The above gases were chosen in the light of the results obtained from previous FALP studies under truly thermalized conditions, i.e. for T-c = T-g = T. These previous experiments showed that the beta for the CCl4 reaction (product Cl-) and SF6 reaction (products SF6-, direct attachment, and SF5-, dissociative attachment, becoming increasingly important with increasing T) were close to the maximum value beta(max), and that the beta for both the CHCl3 dissociative attachment reaction and the C7F14 direct attachment reaction increased with increasing T indicating the presence of activation energy barriers in these reactions. Now the present studies indicate that (i) the beta for both CCl4 and the SF6 reactions decrease with increasing T-c at a rate predicted by s-wave capture theory, and that the SF5- product of the SF6 reaction becomes increasingly important with increasing T-c, (ii) the beta for both the CHCl3 and the C7F14 reactions increase with increasing T-c, but a much greater increase of T-c than T is required to produce a given increase in beta. To explain these experimental observations, a simple model of these attachment reactions has been constructed which is consistent with the experimental data, based on the notion that the energy of the incoming electron is distributed amongst the accessible vibrational states of the molecules, and that this vibrational excitation promotes these particular attachment reactions. A careful analysis of our data indicates that the endothermicity of the dissociative attachment reaction of SF6 producing SF5- is close to 0.12 eV which is consistent with the available thermochemical data.

Abstract: A new analytical technique has been developed to determine from Langmuir probe characteristics the electron number densities, electron energy distribution functions and electron temperatures in thermal and near-thermal afterglow plasmas. This technique utilises a standard personal computer equipped with a simple 12-bit analogue/digital and digital/analogue converters coupled to the Langmuire probe via a specially designed differential amplifier. The energy distribution functions are obtained by numerical differentiation of the probe characteristics using a fast noise-suppressing numerical technique, the mathematical principles of which are discussed in some detail. Some sample data, which have been obtained in truly thermalised helium flowing afterglows and in argon flowing afterglow at elevated electron temperatures, are presented to demonstrate the value of this new analytical technique.

Abstract: Ions are formed in the terrestrial atmosphere (TA) and in interstellar clouds (ISC) by the action of solar/stellar UV and cosmic rays on the ambient neutral atmospheres. The precursor ions so formed develop largely via gas-phase ion chemistry from the simple ions characteristic of the ambient atmospheres to the observed, more complex ions. In the upper TA and in ISC, only biomolecular ion chemistry occurs. In the tenuous upper TA, the ion types remain simple, O+, O-2(+), and NO+ being dominant, and similarly in the tenuous diffuse ISC, ions such as H+, D-2(+), C+, and CH+ are dominant. At the high pressures of the lower TA, termolecular association reactions are important, and the initial ions e.g., O-2(+) and N-2(+) formed by cosmic ray ionization are quickly converted to very complex cluster ions of the type H+ (H(2)0)(n)(bases)(m) with bases including NH3 and CH3CN, and a parallel negative ion chemistry develops from the primary negative ions O- and O-2(-) producing ions like NO3-(H2O)(n)(acid)(m) with acids HNO3 and H2SO4. In the dense ISC, the ion chemistry proceeds to produce polyatomic ions from the most important initial ions C+, H-3(+), and CH3+, and the process of radiative association, the biomolecular analog of termolecular association, is important in producing, for example, ions such as CH(3)(+)M, where M are the common observed interstellar molecules such as the carboxy, cyano, and amino molecules, which are found via this ion chemistry. The major ion neutralization process in the upper TA and in ISC is positive ion-electron recombination, which limits the degree of ionization in these regions, whereas in the lower TA, where negative ions balance the positive ions, the charge neutralization process is ion-ion recombination. (C) 1996 John Wiley & Sons, Inc.

Abstract: Based on the results of recent swarm experiments, it has been proposed that the increase in the cross section for SF5- formation observed at an electron energy, E(e), of about 0.3 eV in electron beam studies of electron attachment to SF6 is due to the combined (opposing) effects of the vibrational heating of the molecule by the attached electron, which enhances the dissociation of the nascent(SF6-)* ion, and the reduction of the cross section for capture (s-wave) of the electron by SF6 with increasing E(e). Further, it has been shown that the dissociation reaction is endothermic by 0.12 eV, and that, contrary to previous suggestions, there is no potential barrier to this dissociation reaction. Now we have carried out electron beam studies of the SF6 attachment reaction in Berlin at gas temperatures, T-g, over the range 300 to 920 K and in Innsbruck at T-g below 300 K. These studies have provided support for the above proposals concerning the appearance of the SF5- peak and for a reaction endothermicity of 0.12 eV. Thus these studies have clarified the doubts about the products of the SF6 attachment reaction at low electron energy.

Abstract: The rate coefficients and ion products have been determined at 300 K for the reactions of H3O+.(H2O)(0,1,2,3) positive ions and OH-.(H2O)(0,1,2) negative ions with six hydrocarbons and six oxygen-containing organic species using a selected ion flow tube (SIFT) for the positive ions and a flowing afterglow (FA) for the negative ions. This study was initiated in support of a major development program of the SIFT and FA as chemical ionization devices for the analysis of trace gases in air and especially of human breath and the vapors emitted by fruits and food products. The H3O+ and OH- ions mostly react with the molecules, MH, via proton transfer, producing respectively MH(2)(+) and M(-) ions, which is ideal for gas analysis. The hydrated hydronium ions and the hydrated hydroxide ions are largely unreactive with the hydrocarbons included in this study, but they are very reactive with the oxygen-containing organic molecules undergoing ligand switching reactions producing mostly MH(2)(+) and M(-) hydrates. The details of the reactions (e.g. the number of H2O molecules either ejected from the intermediate complexes or remaining associated with the MH(2)(+) and MH(-) ��core ions�) are controlled largely by the reaction energy as far as this can be determined. The utility of the reactions of these hydrated ions as chemical ionization agents in atmospheric trace gas analysis is alluded to. Additionally,new FA data on the three-body association reactions of OH- and OH-. H2O with CO2 are presented.

Abstract: The reactions of H3O+ and OH- ions with several hydrocarbons and several oxygen-bearing organic molecules, MH, have been studied using a selected-ion flow tube (SIFT) and a flowing afterglow (FA) apparatus at 300 K. Most of the reactions are fast, proceeding via proton transfer producing a single product, viz. MH(2)(+) for the H3O+ reactions and M(-) or the OH- reactions, but in seven of the twenty-eight reactions two products are observed. In the reaction of H3O+ with trans-2-hexenal only one product is observed whereas in its reaction with the cis-3-hexenal isomer two products are observed. The significance of these observations and the value of the data obtained in this study to trace gas analysis in atmospheric air and on human breath using H3O+ and OH- as chemical ionisation agents is discussed. A by-product of these studies is an estimation of the proton affinity of methylcyclohexane.

Abstract: We have carried out Monte Carlo simulation of the motion of Ar+ ions in the space charge sheath surrounding a cylindrical Langmuir probe. From these simulations the percentage of ions crossing the sheath boundary that are collected by the probe have been determined and thus the ion currents to the probe have been calculated. It is shown that the collisions of ions with neutral helium gas atoms in the sheath increase the percentage of ions collected by the probe above that predicted by collisionless orbital motion limited current (OMLC) theory and that the exponent, x, of the power law dependence, i(+) similar to U-p(x), of the ion current, i(+), on the probe voltage, U-p, increases above the value 0.5 predicted by OMLC theory. The results of the simulations are compared with recent Langmuir probe measurements made in flowing afterglow plasmas.

Abstract: The results of recent laboratory studies of the reactions of H+ and H-3+ with a number of molecular gases are interpreted from the viewpoint of interstellar chemistry. Many of the reactions of these ions result in the ionization and fragmentation of neutral reactant gases. Pseudo-time-dependent calculations of the chemistry in dense molecular clouds indicate that molecular abundances are reduced by the inclusion of such reactions, but generally by less than a factor of 5.

Abstract: We have carried out a thorough theoretical analysis of the cooling and heating processes of the electron gas in Ne, Ar and Kr afterglow plasmas. Thus the rate of relaxation of the electron temperature, T(e), is seen to be in good agreement with the experimental measurements when spatial gradients of T(e) in the early afterglow and heating of the electron gas by superelastic collisions between the electrons and metastable atoms are accounted for. Al low pressures of the rare gases, p(g), the phenomenon of diffusion cooling occurs in which T(e) relaxes to an equilibrium temperature, T(ee), which is less than the gas temperature, T(g). This reduction in T(ee) below T(g) is mirrored in a reduction in the ambipolar diffusion coefficient, D(a), for the rare gas atomic ions and electrons. Thus the D(a) can be calculated as a function of p(g) using the values of T(ee), and when this is done, properly accounting for the heating by metastable atoms, the calculated and experimental values of D(a) in all three rare gas afterglows are seen to be in agreement.

Abstract: The absolute reaction rate coefficients for electron attachment to C-70 have been measured in the electron temperature, T-c, range from 300 to 4500 K using the flowing-afterglow/Langmuir probe technique. A detailed comparison of the electron attaching properties of C-70 with C-60 is made. Thus, whilst electron capture to C-60 occurs only in the p-wave channel at these T-c, it is tentatively reasoned that electron capture by C-70 proceeds preferentially in the s-wave channel below a T-c of about 1000 K and in the p-wave channel and/or the s-wave channel at the higher T-c.

Abstract:

Abstract: A selected ion flow tube study has been carried out at 300 K of the reactions of some atomic and molecular positive and negative halogen ions with Cl2 and Br2 from which the rate coefficients k and ion product distributions have been determined. For the energetic F+ ion reactions, dissociative charge transfer is the dominant process, while for the Cl+ ions, only nondissociative charge transfer occurs. For the less energetic Br+ and I+ reactions, dihalogen molecular ions are important products. All these positive ion reactions proceed quite efficiently, i.e., the k are appreciable fractions of k(c) their respective collisional rate coefficients, except for the reactions of Cl2 with the lower energy ions of the spin-orbit triplet of I+, i.e., I+(P-3)1.0), for which k approximately 0.07k(c) this being due to the endothermicities of the reactions. The molecular ion Cl2+ undergoes rapid nondissociative charge transfer with Br2, a process which is, of course, endothermic for the reaction of Br2+ with Cl2 and so no reaction is observed. The less-energetic atomic negative ion reactions proceed-via atom exchange-in which the atomic negative ion of the reactant molecular species and a dihalogen molecule are produced. For those reactions that are exothermic, the k are, within error, equal to (2/3)k(c), implying that they proceed via complexes which separate statistically back to reactants (1/3) and forward to products (2/3). Both the Br- +Cl2 and Cl- +Br2 reactions are somewhat less efficient (i.e., k < 2/3k(c)) a result of the slight endothermicities of the reactions. Of the molecular negative ion reactions, electron transfer is the major process in the Cl2- reaction with Br2, whereas the reaction of Br2- with Cl2 proceeds relatively slowly producing the triatomic ion BrCl2-.

Abstract: We have determined the dissociative recombination coefficients for vibrationally excited H-3+, alpha(H-3+(upsilon greater-than-or-equal-to 3)), and for vibrational ground-state H-3+, alpha(H-3+(upsilon=0)). Thus, alpha(H3+(upsilon greater-than-or-equal-to 3)) is almost-equal-to 1.3 x 10(-7) cm3 s-1 and alpha(H-3+(upsilon=0)) is (1-2)x 10(-8) cm3 s-1 at 300 K. These findings are in general accordance with theoretical expectations and, as such, resolve a serious controversy. Both these alpha increase only slowly with decreasing temperature. The relevance of these new data to interstellar chemistry is alluded to.

Abstract: The rate coefficients for the reactions of the ions H+, H-2+, H-3+, N+, N2+, Ar+, C+, CH+, CH+2, CH3+, CH4+, and CH5+ with HCI have been measured as a function of reactant ion/reactant neutral average center-of-mass kinetic energy (KE(c.m.)). The measurements were performed using a selected ion flow drift tube operated at 300 K with helium buffer gas. Most of these reactions have rate coefficients close to their collisional values at ambient temperature and all of them exhibit a pronounced KE(c.m.) dependence. A simple model is proposed, in which the measured dependence of the rate coefficients on KE(c.m.) is expressed in terms of the kinetic-energy dependence of the rate unimolecular decomposition of the intermediate complex formed in the ion-neutral collision.

Abstract: Measurements are described of the rate coefficients, beta, for electron attachment to C60 molecules within the electron temperature range 500-4500 K obtained using our flowing afterglow/ Langmuir probe (FALP) apparatus. At a T(e) of 500 K, the beta is small but it increases rapidly with T(e) reaching a value of 3 x 10(-7) cm3 s-1 at 4500 K. Thus an activation energy barrier of 0.26 eV is indicated for electron attachment to C60. The beta at a T(e) of 4500 K is greater than is expected on the basis of s-wave capture theory which we attribute to the large size of the C60 molecule.

Abstract: Prompted by some recent measurements of the recombination coefficient for H-3(+), i.e. alpha(H3+), which indicate a value of approximate to 2 x 10(-7) cm(3) s(-1) at 300 K for ground vibrational state ions, i.e. about a factor of ten greater than our previous FALP determination less than or equal to 2 x 10(-8) cm(3) s(-1), we have made a further detailed study of this very important interstellar recombination reacation using our improved FALP apparatus. Thus we have shown that alpha(H-3(+)(v greater than or equal to 3)) ions do indeed recombine quite efficiently, a mean recombination coefficient at 300 K being approximate to 1.3 x 10(-7) cm(3) s(-1), but that vibrationally-relaxed ions recombine much more slowly, alpha(H-3(+)(v = 1, 0)) being approximate to 3 x 10(-8) cm(3) s(-1) and alpha(H-3(+)(v = 0)) being somewhat smaller at (1-2) x 10(-8) cm(3) s(-1) at 300 K. Measurements at 210 and 140 K indicated a slow increase of alpha(H3+) with decreasing temperature, the increase being less than a factor of 2 for both alpha(H-3(+)(v greater than or equal to 3)) and alpha(H-3(+)(v = 1, 0)) between 300 and 140 K. Values of alpha(D-3(+)) were also obtained at 300 K only. The values obtained for both the rapidly-recombining and the slowly-recombining D-3(+) ions were somewhat smaller than the corresponding values for H-3(+). In addition to these studies, we have also re-measured the alpha values at both 300 and 100 K for HCO+, N2H+ and CH5+ which are also imporant interstellar ions. The values obtained are in reasonable agreement with our previous FALP measurements, but our alpha(HCO+) and alpha(N2H+)are lower by factors of 2 and 3 respectively than the recent measurements made in a pulsed afterglow experiment.

Abstract: The rate coefficients k have been determined as a function of reactant ion/reactant molecule centre-of-mass energy E(r) for the reactions of C+, CH+ and CH2+ with both HCl and CO2 in a selected ion flow drift tube (SIFDT) apparatus. In these experiments, the carrier gas was pure helium at a temperature of 300 K. For low values of E(r), the k values are close to the respective collisional rate coefficients k(c) but the k decreases with increasing E(r). These results are interpreted in terms of a simple model by which the reactions are considered to proceed via the formation of long-lived complexes which decompose back to the reactants or forward to products, the unimolecular decomposition rate coefficients for these reactions being k(-1) and k(2) respectively. It is found that a power law relation of the form k(-1)/k(2). = const x E(r)(m) closely describes each reaction. An attempt is made to rationalise the values of the indices m obtained for each reaction in terms of the number of rotational degrees of freedom in the separated reactants, and then some support is apparently evident for the theoretical indication that CO2 is a ��bent� molecule. The k for the slower reaction of CH3+ with HCl was measured in the SIFDT in both helium and argon carrier gas, and the results compared with previous results obtained in a VT-SIFT apparatus under truly thermalised conditions. The combined results of these studies are used to indicate which form of energy in the reactants (internal or translational) influences the rate at which the reaction proceeds.

Abstract: We have developed the flowing afterglow-langmuir probe (FALP) technique to allow the rapid and accurate determination of electron energy distribution functions f(E) and electron temperatures T-e in flowing afterglow plasmas. In helium carrier gas, which has been used for almost all the previous FALP studies f(E) is closely Maxwellian and T-e is always close to the carrier gas temperature T-g (variable within the range 80-600 K). However, in argon carrier gas, T-e can be much greater than T-g and f(E) may not be Maxwellian. We have learned how to control T-c within the range from T-g up to about 3000 K in argon carrier gas and thus we are now able to study attachment and recombination processes over this range of T-g and T-e. As a first study, we have determined the coefficient beta for dissociative electron attachment to CF3Br (products Br- and CF3) over the accessible ranges of T-g and T-e. The beta increases rapidly with T-g and decreases with T-e, being described by the relation beta = 8 x 10(-7) (T-e/300K)(-0.75) exp [-(1150K/T-g)] cm(3) s(-1) within these T-g and T-e ranges. Departures of f(E) from Maxwellian can occur in the argon afterglow plasmas when the electron number density n(c) is less than 10(7) cm(-3) at which the electron/electron collision frequency is low. This is very evidence when efficient electron attachment is occurring, and it is dramatically illustrated by observing f(E) as SF6 is introduced into the plasma which predominantly removes the low energy electrons from the electron gas.

Abstract: A selected ion flow tube (SIFT) study of the reactions of the rare gas positive ions He+, Ne+, Ar+, Kr+ and Xe+ with Cl-2 and Br-2 has been carried out at 300 K from which the rate coefficients k and ion product distributions have been determined. For the very exothermic He+ and Ne+ ions reactions, dissociative charge transfer is the only observed process. For the less exothermic reaction of Ar+ with Cl-2 both dissociative and non-dissociative charge transfer occurs. In the reaction of Ar+ with Br-2 the main ion product is Br+ but a small percentage of the stable rare gas-halogen dimer ion ArBr+ was observed. Ions in two spin-orbit states of Kr+ and Xe+ (i.e. P-2(3/2), P-2(1/2)) react at different rates with Cl-2 and Br-2 the P-2(1/2) excited state ions react more slowly than the P-2(1/2) ground slate ions, consistent with previous results for the reactions of these ions with other molecules. The dominant process is charge transfer, which is dissocialive in the case of Kr+ + Br-2. Production of the stable ions KrCl+, KrBr+, XeCl+ and XeBr+ takes place exclusively in reactions of the ions in the P-2(1/2) states. The secondary reactions of these rare gas-halogen ions with Cl-2 and Br-2 produce the triatomic ions Cl-3(+) and Br-3(+) which are unreactive with their parent ions. The rate coefficients of these secondary reactions have also been determined.

Abstract: Measurements are described of the dissociative recombination coefficients alpha of O-2(+) and NO+ at electron temperatures, T-e within the range 300 K less than or equal to T-e less than or equal to 2000 K. These measurements have been achieved using the upgraded flowing afterglow-Langmuir probe (FALP) technique by which it is now possible to rapidly determine the T-e (and also the electron energy distribution function) and the electron number density n(e) at any point along the axis of the flowing afterglow plasma. The elevated T-e (above the carrier gas temperature T-g) are readily achievable in argon carrier gas but not in helium carrier gas in which T-c remains equal to T-g. The alpha for both O-2(+) and NO+ are seen to vary with T-e in power-law fashions, i.e. alpha(O-2(+)) approximate to T-e(-0.65) and alpha(NO+) approximate to T-e(-0.85) over the range of T-e investigated, being the same as the power-law variations observed for isothermal conditions (i.e. T-g = T-e = T-i, the ion temperature) in our previous FALP study within the range 200 K less than or equal to T-g less than or equal to 600 K. The implication of these results is that T-e (not T-i) primarily determines alpha(O-2(+) ) and alpha(NO+) in this temperature regime, in accordance with theoretical expectations. The ranges of T-g and T-e over which these cr have now been determined are precisely those required for ionospheric deionization studies. The results obtained are compared with previous measurements, including some ionospheric in-situ measurements of alpha(NO+) as a function of T-e, and, in general, the agreement between the previous and the present measurements is good.

Abstract: The reactions of C2H2+ with H-2 and C2D2+ + D-2 have been studied in a selected ion flow drift tube (SIFDT) over a range of centre-of-mass energies E(c) from thermal (300 K) to a few tenths of an electron volt. The reactions proceed along parallel bimolecular and termolecular channels producing C2H3+ (C2D3+) and C2H4+ (C2D4+). The relative importance of the bimolecular channel increases and that of the termolecular channel decreases with increasing E(c) in accordance with previous data. The rates for the bimolecular reactions increase as the C=C stretching vibrations in the reactant ion are excited in collisions with the helium carrier gas atoms in the SIFDT at higher E(c) values, consistent with other work in which these vibration modes are selectively excited using laser ionisation. The question is addressed as to whether the atom abstraction reactions are exothermic or endothermic. Based on the new experimental data, some recent ion trap data and previous data on the reaction of C-2 H-3(+) with H atoms, it is concluded that the reactions are slightly endothermic, and it is tentatively suggested that a potential barrier also exists to the reactions. The interstellar implications of these results are briefly referred to.