Product ion distributions for the reactions of NO(+) with some physiologically significant volatile organosulfur and organoselenium compounds obtained using a selective reagent ionization time-of-flight mass spectrometer

The findings of this study are of particular importance for data interpretation in studies of volatile organosulfur and volatile organoselenium compounds employing SRI-TOF-MS in the NO(+) mode.

Product ion distributions have been investigated by a SRI-TOF-MS instrument at an E/N in the drift tube reactor of 130 Td for both dry air and humid air (4.9% absolute humidity) used as the matrix gas. The investigated species were five monosulfides (dimethyl sulfide, ethyl methyl sulfide, methyl propyl sulfide, allyl methyl sulfide and methyl 5-methyl-2-furyl sulfide), dimethyl disulfide, dimethyl trisulfide, thiophene, 2-methylthiophene, 3-methylthiophene, methanethiol, allyl isothiocyanate, dimethyl sulfoxide, and two selenium compounds - dimethyl selenide and dimethyl diselenide.

Charge transfer was seen to be the dominant reaction mechanism in all reactions under study forming the M(+) cations. For methanethiol and allyl isothiocyanate significant fractions were also observed of the stable adduct ions NO(+) M, formed by ion-molecule association, and [M-H](+) ions, formed by hydride ion transfer. Several other minor product channels are seen for most reactions indicating that the nascent excited intermediate (NOM)(+) * adduct ions partially fragment along other channels, most commonly by the elimination of neutral CH3 , CH4 and/or C2 H4 species that are probably bound to an NO molecule. Humidity had little effect on the product ion distributions. Conclusions: The findings of this study are of particular importance for data interpretation in studies of volatile organosulfur and volatile organoselenium compounds employing SRI-TOF-MS in the NO(+) mode.