The reactions of H3O+, NO+, and O with nineteen ester compounds occurring naturally in plants, and having important flavourant properties, were examined using selected ion flow tube mass spectrometry (SIFT-MS). The H3O+ reactions primarily generate [R1COOR2·H]+, and may also produce [R2]+ fragment ions and/or fragmentation within the ester linkage. Collisional association/adduct ions, [R1COOR2·NO]+, are the main products formed in the NO+ reactions, although the carboxyl fragment ion is also detected frequently. The identification of the parent compound may be made more easily in the H3O+ and NO+ reactions. The inclusion of O reactions in the analysis provides additional information, which may be applied when the identity of a parent compound cannot be determined solely from the H3O+ and NO+ analysis. Consideration of the product ions generated with the three precursors suggests that SIFT-MS can differentiate between many of the esters investigated, including isomers, although the product ions generated in the reactions with some esters are too similar to allow independent quantification. Our data therefore suggest that SIFT-MS may be a useful tool to rapidly analyse and quantify flavourant esters in complex gas mixtures. Copyright © 2010 John Wiley & Sons, Ltd.