A selected ion flow tube study of the reactions of H 3O +, NO +, and O 2+ with saturated and unsaturated aldehydes and subsequent hydration of the product ions

Abstract

We have carried out a selected ion flow tube (SIFT) study of the reactions of H 3O +, NO +, and O 2 + ions with several saturated and unsaturated aldehydes. This study is mainly directed toward providing the essential data for a projected SIFT mass spectrometry (SIFTMS) study of the volatile emissions from cooked meats, which always include aldehydes. Thus, it is necessary to know the rate coefficients and the product ions of the reactions of the above-mentioned ions, used as the precursor ions for SIFTMS analyses, with the aldehydes, if proper identification and quantification of the emitted species are to be achieved. The results of this study show that the reactions of H 3O + with the aldehydes, M, result in the protonated molecules MH + and for the saturated aldehydes also in (M - OH) + ions resulting from the loss of a H 2O molecule from the nascent MH + ion. The NO + reactions invariably proceed via the process of hydride ion, H −, transfer producing (M - H) + ions, but parallel minor association product ions NO + · M are observed for some of the unsaturated aldehyde reactions. The O 2 + reactions proceed by way of charge transfer producing nascent M + ions that partially dissociate producing fragment ions. Because water vapour is invariably present in real samples analysed by SIFTMS, the current experiments were also carried out following the introduction of humid laboratory air into the helium carrier gas of the SIFT. Thus, the reactions of the product ions that form hydrates were also studied as a prelude to future SIFTMS studies of the (humid) emissions from cooked meats.