Abstract Proton-transfer-reaction time-of-flight mass spectrometry has been employed in a 12 months breath gas analysis study to describe the breath composition of 19 cigarette smoking and 53 non-smoking women. The most prevalent constituents were acetone (1.8 ppmv), methanol (310 ppbv), isoprene (280 ppbv), ethanol (130 ppbv), acetaldehyde (90 ppbv) and acetic acid (70 ppbv). Smokers showed the largest signal increase in acetonitrile (ratio smoker/non-smoker 29), benzene (ratio 11), 2-methylfuran (ratio 8) and 2,5-dimethylfuran (ratio 7). Calibration gas measurements allowed the instruments performance regarding precision and accuracy of ion mass-to-charge, m/z, and concentration accuracy measurement to be assessed. The standard deviation of the concentration measurements was 14% or smaller (with the exception of ethanol) with no trend in this variation of sensitivity. The limit of detection (LOD) lay in the sub ppbv range, based on an integration time of 2 s. The m/z accuracy was better than 0.0016 (or less than 29 ppm of the ion mass) throughout the study. The standard deviation of the measured m/z was less than 0.0025 and the coefficient of variation was less than 29 ppm. Keywords PTR-TOF-MS, Smokers’ breath, Breath volatile organic compounds, \{VOCs\}

A method for analysis of volatile organic compounds (VOCs) from microbial cultures was established using proton transfer reaction-mass spectrometry (PTR-MS). A newly developed sampling system was coupled to a PTR-MS instrument to allow on-line monitoring of VOCs in the dynamic headspaces of microbial cultures. The novel PTR-MS method was evaluated for four reference organisms: Escherichia coli, Shigella flexneri, Salmonella enterica, and Candida tropicalis. Headspace VOCs in sampling bottles containing actively growing cultures and uninoculated culture medium controls were sequentially analyzed by PTR-MS. Characteristic marker ions were found for certain microbial cultures: C. tropicalis could be identified by several unique markers compared with the other three organisms, and E. coli and S. enterica were distinguishable from each other and from S. flexneri by specific marker ions, demonstrating the potential of this method to differentiate between even closely related microorganisms. Although the temporal profiles of some VOCs were similar to the growth dynamics of the microbial cultures, most VOCs showed a different temporal profile, characterized by constant or decreasing VOC levels or by single or multiple peaks over 24 h of incubation. These findings strongly indicate that the temporal evolution of VOC emissions during growth must be considered if characterization or differentiation based on microbial VOC emissions is attempted. Our study may help to establish the analysis of VOCs by on-line PTR-MS as a routine method in microbiology and as a tool for monitoring environmental and biotechnological processes.

The storage capability of Tedlar(R) bags for gaseous compounds was assessed using on-line proton-transfer-reaction mass spectrometry (PTR-MS). Sample bags were filled with a mixture of volatile organic compounds (VOCs) at known quantities in the ppbv range. The test gas included alcohol, nitrile, aldehyde, ketone, terpene and aromatic compounds. PTR-MS enabled frequent bag-direct measurements of compound abundances over a 70 h storage period. Concentrations of all compounds decreased with bag storage time, with compound-specific decay rates. The most rapid decline in concentration levels was seen for water vapour in the bag, i.e. sample humidity. Such a decrease is particularly relevant for breath-gas samples, where water vapour content is high. Compound losses were attributed to a combination of adsorption to and diffusion through the bag walls. Storage property observations suggest that sample analyses made within 10 h of sampling offer adequate sample authenticity replication. Based on observations, an appropriate bag-cleaning procedure was established and assessed. Results indicated that acceptable bag cleanliness for breath-gas sampling is achievable.

AN ON-LINE PTR-MS SYSTEM FOR THE SENSITIVE REAL-TIME DETECTION OF VOLATILE METABOLITES FROM MICROBIAL CULTURES

Benzene and acetonitrile are both present in greater concentrations in the breath of smokers than in non-smokers. The concentrations of these neutrals can be readily detected in the gas phase by their proton transfer reactions with H3O+. The concentration of benzene in the breath of smokers rapidly decreases with the time since the last cigarette was smoked, declining to values similar to those of non-smokers within an hour. In contrast, the concentration of acetonitrile in the breath of smokers takes nearly a week to decrease to that of non-somokers, once smoking stops. Thus the analysis of acetonitrile in the breath is a most suitable indicator of whether a given subject is or is not a smoker.