Quantification of pentane in exhaled breath, a potential biomarker of bowel disease, using selected ion flow tube mass spectrometry
Abstrakt
RATIONALE: Inflammatory bowel disease has a relatively large incidence in modern populations and the current diagnostic methods are either invasive or have limited sensitivity or specificity. Thus, there is a need for new non-invasive methods for its diagnosis and therapeutic monitoring, and breath analysis represents a promising direction in this area of research.
Specifically, a method is needed for the absolute quantification of pentane in human breath. METHODS: Selected ion flow tube mass spectrometry (SIFT-MS) has been used to study the kinetics of the O-2(+) reaction with pentane.
Product ions at m/z 42 and 72 were chosen as characteristic ions useful for the quantification of pentane and the reactivity of these ions with water vapour was characterized. A pilot study has been carried out of pentane in the exhaled breath of patients with Crohn's disease (CD) and ulcerative colitis (UC) and of healthy volunteers.
RESULTS: Accurate data on the kinetics of the gas phase reaction of the O-2(+BULLET OPERATOR) ions with pentane have been obtained: rate coefficient 8 x 10(-10) cm(3) s(-1) (+/- 5%) and branching ratios into the following product ions C5H12+BULLET OPERATOR (m/z 72, 31%); C4H9+ (m/z 57, 8%); C3H7+ (m/z 43, 40%), C3H6+BULLET OPERATOR (m/z 42, 21%). A method of calculation of absolute pentane concentration in exhaled breath was formulated using the count rates of the ions at m/z 32, 42, 55 and 72.
Pentane was found to be significantly elevated in the breath of both the CD (mean 114 ppbv) and the UC patients (mean 84 ppbv) relative to the healthy controls (mean 40 ppbv).