Selected ion flow tube study of the reactions of H 3 O + 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 H3 O+ and NO+ with alcohol molecules in the presence of water molecules needs to be understood and quantitatively described.

METHODS: 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 (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 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.

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 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.