Selected ion flow tube study of the reactions of H3O+ and NO+ with a series of primary alcohols in the presence of water vapour in support of selected ion flow tube mass spectrometry

RATIONALE: Alcohols are often present in foods and other biological media, including exhaled breath, urine and cell culture headspace. For their analysis by selected ion flow tube mass spectrometry (SIFT-MS), the ion chemistry initiated by the reactions of the reagent ions H3O+ and NO+ with alcohol molecules in the presence of water molecules needs to be understood and quantitatively described. METHODS: The reactions of H3O+ and NO+ ions have been studied with the primary alcohols, methanol, ethanol, 1-propanol, 1-butanol, 1-pentanol and 1-hexanol, under the conditions used for SIFT-MS analyses (1 Torr He; 0.1 Torr air sample; 300 K) and over a range of sample gas humidity from 1% to 5.5%. RESULTS: The H3O+ reactions led to the formation of protonated alcohol molecules MH+ and their hydrates MH+(H2O)(1,2,3) and ( MH+-H2O) fragment ions. The NO+ reactions were observed to proceed mainly via hydride ion transfer, resulting in the formation of [M-H](+) product ions. Formation of the NO+M adduct ions was also observed due to ligand switching between the NO+( H2O)(1,2) hydrated reagent ions and M, and via direct NO+/M association in the case of ethanol. The variation in the percentages of the hydrated product ions with the air sample humidity is reported. CONCLUSIONS: This detailed study has provided the kinetics data, including the secondary hydrated ion product distributions, for the reactions of a number of volatile primary alcohols with the SIFT-MS reagent ions H3O+ and NO+, which allows their analyses by SIFT-MS in humid air and also helps in the interpretation of proton transfer reaction (PTR)-MS data. Copyright (c) 2016 John Wiley & Sons, Ltd.