Atmospheric concentrations of isoprene (2-methylbutadiene) in environmental research and in exhaled breath for medical research are usually measured by soft chemical ionization mass spectrometry that relies on a knowledge of the kinetics of the gas phase reactions of H3O+, NO+ or O2+• ions with isoprene molecules. Thus, we have carried out an experimental study of the rate coefficients, k, and product ions distributions for such reactions over a range of ion-molecule interaction energy, Er, (0.05-0.8 eV) in a helium-buffered selected ion flow-drift tube, SIFDT. It is found that contrary to the ion-induced dipole capture model, k for the NO+ and O2+• charge transfer reactions almost doubled over the E r range, while k for the H3O+ proton transfer reaction did not significantly change with E r, as predicted. These results reveal that the reaction mechanism involving ion-molecule capture forming an intermediate complex does not properly describe charge transfer to isoprene molecules. It is important to account for this increase in k with E r in these isoprene charge transfer reactions, and probably for other such reactions, when using drift tube reactors for trace gas analysis.

A novel, non-invasive technique is reported for determining the numbers of cells in a culture by quantifying dimethyl sulphide (DMS) in the culture headspace as produced by the cellular enzymatic reduction of dissolved dimethyl sulphoxide (DMSO). Measured DMS concentrations, as performed using selected ion flow tube mass spectrometry (SIFT-MS), in the headspace of 2D and 3D cultures of four cell lines, viz. HEK293 (kidney), MG63 (bone), hepG2 (liver) and CALU-1 (lung), linearly correlate with starting cell number. Clear differences in the rates of production of DMS by the four cell types in both the 2D and 3D situations are seen. This novel analytical technique for cell enumeration offers a significant contribution to quality assessment across cell-based research and industry, including analysis of large scale culture systems, and for routine cell biology research.

Hydrogen cyanide (HCN) and 2-aminoacetophenone (2-AA; H2NC6H4COCH3) are possible biomarkers of pulmonary Pseudomonas aeruginosa (PA) infection that could be used in an exhaled breath test. All factors affecting their production need to be investigated, including the culture conditions: planktonic (free-floating) or biofilm (non-motile communities attached to a solid surface). In vivo, the change from planktonic to biofilm growth is signalled when a certain population density is reached. Using selected ion flow tube mass spectrometry, SIFT-MS, we have analysed HCN and 2-AA produced by 12 genotyped PA samples, cultured under both planktonic and biofilm conditions after 24, 48, 72 and 96 hours of incubation. The 12 samples included 3 different strains (genotypes), 50% of which had a mucoid phenotype and 50% had a non-mucoid phenotype. All samples produced significant concentrations of HCN; median (25th to 75th percentiles, IQR) concentration: 144 (61–512) parts-per-billion by volume (ppbv). Multivariate analysis showed HCN production varied dependent on genotype (p = 0.0014), culture duration (p = 0.005) and phenotype (p < 0.001) but not culture conditions (planktonic/biofilm). Much smaller concentrations of 2-AA were detected, median (IQR) concentration 1.8 (1.3–3) ppbv, despite which, multivariate analysis showed production was affected by genotype (p < 0.001) and culture duration (p = 0.007) but not phenotype or culture conditions. These data show that biofilm formation does not affect HCN production by PA and supports its use as a biomarker of PA infection. The concentrations of 2-AA are much lower than previous studies have shown. The reason for this is unclear but it raises questions about its suitability as a biomarker of PA infection.

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.

The absolute reaction rate coefficients for electron attachment to C70 have been measured in the electron temperature, Te, range from 300 to 4500 K using the flowing-afterglow/Langmuir probe technique. A detailed comparison of the electron attaching properties of C70 with C60 is made. Thus, whilst electron capture to C60 occurs only in the p-wave channel at these Te, it is tentatively reasoned that electron capture by C70 proceeds preferentially in the s-wave channel below a Te of about 1000 K and in the p-wave channel and/or the s-wave channel at the higher Te.

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.