Selected ion flow tube, SIFT, studies of the reactions of H3O+, NO+ and O2+ with some biologically active isobaric compounds in preparation for SIFT-MS analyses

A study of the reactions of H3O+, NO+ and O2+ ions with two groups of four isobaric, biologically active compounds with molecular weights, MW, of 86u and 88u has been carried out using the selected ion flow tube, SIFT, technique in preparation for the analyses of these compounds in the headspace of bacterial and cell cultures using SIFT-MS. These compounds are: MW 86u: 2,3 butanedione (diacetyl), C4H6O2; allyl ethyl ether, C5H10O, cyclopropane carboxylic acid, C4H6O2: γ-butyrolactone, C4H6O2. MW 88u: 3-hydroxybutanone (acetoin), C4H8O2; n-butyric acid, C4H8O2; ethyl acetate, C4H8O2; pyruvic acid, C3H4O3. All 24 reactions proceed at the gas kinetic rate, the dominant primary product ions of the H3O+ reactions being the protonated reactant molecules, MH+ with a common mass-to-charge ratio, m/z, in each group of isobaric compounds; those of the NO+ reactions being the adduct ions, NO+M, also with a common m/z value; for the O2+ ion reactions, fragmentation ions of the nascent parent ion M+ are produced. SIFT-MS analysis of each compound individually is straightforward, but when more than one isobaric compound is present, SIFT-MS analyses become more challenging. However, hydration of some, but not all, of the primary MH+ and NO+M primary ions occurs, variously generating MH+(H2O)1,2 and NO+MH2O ions, and the occurrence/non-occurrence of these hydrates can assist in distinguishing between some of the isobaric compounds. From the kinetic data obtained in this study, the required SIFT-MS kinetics library entries for each compound can be constructed that allow their quantification. As an example, SIFT-MS spectra are presented relating to the analysis of the headspace of incubated yoghurt, which show the presence of several volatile organic compounds, including acetoin and diacetyl.

Reactions of H3O+, NO+ and O2+ have been studied with four isobaric compounds, MW 86u, 2,3 butanedione or diacetyl, C4H6O2; allyl ethyl ether, C5H10O, cyclopropane carboxylic acid, C4H6O2: γ-butyrolactone, C4H6O2 and with four MW 88u compounds, 3-hydroxybutanone or acetoin, C4H8O2; n-butyric acid, C4H8O2; ethyl acetate, C4H8O2; pyruvic acid, C3H4O3.Figure optionsDownload high-quality image (97 K)Download as PowerPoint slideResearch highlights
► Data are reported for SIFT-MS quantification of eight biologically active compounds.
► Isobaric compounds can be distinguished by hydration of characteristic product ions.
► Pyruvic acid can be analysed in the headspace of its aqueous solution using SIFT-MS.
► Acetoin and diacetyl are quantified in the headspace above incubated yoghurt.