A study of sulfur-containing compounds in mouth- and nose-exhaled breath and in the oral cavity using selected ion flow tube mass spectrometry

Abstract

We have carried out a selected ion flow tube mass spectrometry (SIFT-MS) study of the concentrations of the sulfur-containing compounds H2S (using H3O+ precursor ions), CH3SH (H3O+), (CH3)2S (O2+), (CH3)2S2 (NO+) and CS2 (O2+) in single exhalations of mouth-exhaled breath and nose-exhaled breath and in the static gas in the oral cavity for two healthy volunteers. The primary purpose of the study was to show how compounds present in breath at levels as low as a part per billion (ppb) can be identified and quantified if the overlap of ‘impurity’ isobaric ions with the analytical product ions for each trace compound is identified and accounted for. The H2S measurements are straightforward using H3O+ precursor ions, since no overlapping ions are recognized and its breath concentration is relatively high at typically 20–70 ppb. Thus, its concentration distribution for two healthy volunteers has been obtained over a period of a few weeks. The situation is very similar for CH3SH, but to analyse this compound we had to study the kinetics of its reactions with the SIFT-MS reagent ions H3O+, NO+ and O2+ in order to provide the required kinetics library data for this compound. It is seen that CH3SH, (CH3)2S and (CH3)2S2 are present in the mouth breath/cavity at lower levels of <10 ppb. The measurements of the levels of H2S and these compounds in the nose-exhaled breath and the closed mouth indicate that they are largely produced in the oral cavity, although there is some indication that (CH3)2S is partially systemic in these two volunteers. It was not possible to quantify CS2 in the breath because of serious interference (overlapping ions) due to the presence of carbon dioxide and acetone that inevitably occur in exhaled breath. This study paves the way for the accurate analysis of these sulfur compounds in halitosis and potentially for probing the diseased state, especially liver disease, by breath analysis. To demonstrate the simplicity of measuring these compounds when they are present at levels of about 100 ppb and greater, data are presented on the emissions of these sulfur-containing compounds from Pseudomonas bacterial cultures in vitro.