Pentane and isoprene in expired air from humans: gas-chromatographic analysis of single breath.

Both pentane and isoprene are excreted in human breath. Although pentane is considered an index of lipid peroxidation, the significance of isoprene is unknown. Having a similar boiling point, these two hydrocarbons are difficult to separate by gas chromatography. We separated pentane from isoprene on both a Poraplot Q and a Poraplot U column, injecting single-breath samples directly into a gas chromatograph. The breath samples were pressurized to 800 mmHg to increase the amount of sample volume delivered to the column. In a group of 43 healthy volunteers, the concentrations of end-expiratory pentane and isoprene were 0.57 +/- 0.3 and 7.05 +/- 3.53 nmol/L, respectively. There was a significant linear correlation (r = 0.57, P < 0.0001) between age and pentane concentration in expired air; isoprene showed no correlation with age or pentane concentrations. The age-related increase in pentane production suggests that oxidative stress may play a role in the aging process in humans. The method described should allow for rapid, inexpensive, serial measurement of expired pentane and isoprene.