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.

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.

Rapid quantification of breath deuterium abundance by flowing afterglow mass spectrometry (FA-MS) enables accurate measurement of total body water (TBW), which combined with other techniques such as bioelectrical impedance analysis (BIA) and anthropometrics enables near-subject assessment of body composition. This study assessed the comparative reproducibility and inter-relationship of these methods in healthy subjects over 12 months. Detailed bedside composition was performed in 22 subjects, (10 male) aged 28-79 with body mass index (BMI) ranging from 21-38 at baseline and again at one year. Techniques included FA-MS deuterium dilution, BIA, skin-fold thickness (SFT) and soft tissue ultrasound measurement of fat and muscle depth. Short-term reproducibility for each method was established. Within and between technique comparisons of measurement were made from Pearson's linear regression, coefficient of variation (CV) and Bland-Altman analysis. Weight and TBW estimated by FA-MS, BIA and SFT at baseline and one year later were highly correlated (R2 = 0.96-0.98), slope 1.02-1.03, CV = 4.5-11.6%. Systematic errors between the different methods in determining TBW were effectively identical at baseline and after one year. There was a tendency for subjects to gain weight during the study period, due to an increase, predominantly in younger women, of body water (FA-MS and SFT) and loss of upper body fat (ultrasound). BIA was relatively insensitive to these changes. It is concluded that over a 12-month period, TBW determined by FA-MS deuterium breath analysis has reproducibility similar to conventional weighing. The stability of between method errors would suggest that these techniques might be used in conjunction with each other in the longitudinal determination of body composition and so detect relatively subtle changes. The value of including an absolute determinant of TBW by FA-MS that is independent of the need to employ population derived equations, appears to be of value in the near-subject determination of body composition as required in clinical practice.

We have carried out a selected ion flow tube (SIFT) study of the reactions of H3O+, NO+ and O2+• 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 exothermic 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 SIFT-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 O2+• 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.

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.

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.

We have carried out a selected ion flow tube, SIFT, study of the reactions of H3O+, NO+ and O2+ 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 O2+ 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 O2+ with CH3C(O)OOH molecules. It turns out that both H3O+ and O2+ 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.

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.

INTRODUCTIONMechanisms of water flow across the peritoneal membrane include diffusion, convection, and reabsorption.OBJECTIVESTo understand these processes more clearly we have developed a method to measure transport of water across the peritoneal membrane.METHODSAn 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.RESULTSThe 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%.CONCLUSIONTransport 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.

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.

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.

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 O2+ 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.

The catalytic oxidation of methane over supported nickel catalysts has been studied using conventional catalytic reactor measurements, temperature programmed reaction spectroscopy and gas pulsing experiments. The influence of support material, catalyst pre-treatment and operating temperature have been studied. The nature of the support material has a large influence on the subsequent activity and CO selectivity of the nickel catalysts. Temperature programmed measurements have been used to study methane activation, the surface reaction pathways and to evaluate the nature and level of any carbon species deposited during reaction. Temperature programmed oxidation reveals several types of carbon are formed on the catalyst during catalytic methane oxidation. Gas pulsing experiments have been carried out at different reaction temperatures to determine how the initial methane conversion, product selectivity and surface carbon yield vary as a function of contact time, and show that metallic nickel provides the active site for methane partial oxidation.

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 multifre- quency bioelectrical impedance analysis, skinfold-thickness (SFT) measurements, and both recent and historical published regres- sion equations. Design: After baseline measurement of breath deuterium abun- dance, 24 healthy subjects ingested 0.3 g D2O/kg body wt. A sec- ond breath sample was taken after 3 h to measure the increase in deuterium, from which TBW was calculated. Bioelectrical imped- ance 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 sub- jects is emphasized. Am J Clin Nutr 2002;76:1295-301.