Selected ion flow tube study of the reactions of H3 O+ and NO+ with a series of primary alcohols in the presence of water vapour in support of selected ion flow tube mass spectrometry.

Abstract

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 H3 O+ and NO+ with alcohol molecules in the presence of water molecules needs to be understood and quantitatively described. The reactions of H3 O+ 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 (1Torr He; 0.1Torr air sample; 300K) and over a range of sample gas humidity from 1% to 5.5%. The H3 O+ reactions led to the formation of protonated alcohol molecules MH+ and their hydrates MH+ (H2 O)1,2,3 and (MH+ -H2 O) 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+ (H2 O)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. 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 H3 O+ 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 © 2016 John Wiley & Sons, Ltd.