Infection by Pseudomonas aeruginosa (PA) is a major cause of morbidity and mortality in patients with
cystic fibrosis (CF). Breath analysis could potentially be a useful diagnostic of such
infection, and analyses of
volatile organic compounds (VOCs) emitted from PA cultures are an important part of the search for volatile breath markers of PA lung
infection. Our pilot experiments using solid-phase microextraction,
SPME and gas chromatography/mass spectrometric (GC/MS) analyses of volatile compounds produced by PA strains indicated a clear presence of
methyl thiocyanate. This provided a motivation to develop a method for real-time online quantification of this compound by selected ion flow tube mass spectrometry, SIFT-MS. The kinetics of reactions of H(3)O(+), NO(+) and O(2)(+•) with
methyl thiocyanate at 300 K were characterized and the characteristic product
ions determined (
proton transfer for H(3)O(+), rate constant 4.6 × 10(-9) cm(3) s(-1); association for NO(+), 1.7 × 10(-9) cm(3) s(-1) and nondissociative charge transfer for O(2)(+•) 4.3 × 10(-9) cm(3) s(-1)). The kinetics library was extended by a new entry for
methyl thiocyanate accounting for overlaps with isotopologues of hydrated hydronium
ions. Solubility of
methyl thiocyanate in water (Henry's law constant) was determined using standard reference solutions and the linearity and limits of detection of both SIFT-MS and
SPME-GC/MS methods were characterized. Thirty-six strains of PA with distinct genotype were cultivated under identical conditions and 28 of them (all also producing HCN) were found to release
methyl thiocyanate in headspace concentrations greater than 6 parts per billion by volume (ppbv). SIFT-MS was also used to analyze the breath of 28 children with CF and the concentrations of
methyl thiocyanate were found to be in the range 2-21 ppbv (median 7 ppbv).