The use of proton transfer reaction mass spectrometry for analysis of volatile organic compounds in breath and microbial headspace

The proton transfer reaction mass spectrometer (PTR-MS) was used to analyse volatile organic compounds (VOCs) in human breath and the headspace above microbial cultures. Real-time expirograms of acetone, isoprene and methanol show that end-expired VOC concentration depends on duration of exhalation so a robust method of breath sampling based on cyclic rebreathing was developed. Concentrations of VOCs in arterial (CAB) and venous blood (CVB) and breath (CBr), were measured in 10 healthy volunteers. Mean (range) CBr, CAB and CVB are 1090 (515-2335) ppbv, 26 (10-73) μmol/1 and 18 (9-39) μmol /1 respectively for acetone. For isoprene, the corresponding values are 465 (308-702) ppbv, 6.8 (3.7-11) nmol/1 and 14 (5.5-30) nmol/l. In-vivo blood/breath ratios were calculated and were 580 (280 -1060) for acetone and 0.47 (0.22 - 0.77) for isoprene. The limits of agreement between blood concentrations of acetone and isoprene in blood and breath were determined. A significant inter-individual correlation was found between breath and arterial blood for acetone but not for isoprene. Headspace above three types of nutrient broths inoculated with Staphylococcus aureus was compared with uninoculated broths. VOC emissions from the cultures were measured over 6 hours. The same VOCs were observed for each cultured broth but the time evolution was different