title: Sulfides: chemical ionization induced fragmentation studied with proton transfer reaction-mass spectrometry and density functional calculations.
abstract: We report the energy-dependent fragmentation patterns upon protonation of eight sulfides (organosulfur compounds) in Proton Transfer Reaction-Mass Spectrometry (PTR-MS). Studies were carried out, both, experimentally with PTR-MS, and with theoretical quantum-chemical methods. Charge retention usually occurred at the sulfur-containing fragment for short chain sulfides. An exception to this is found in the unsaturated monosulfide allylmethyl sulfide (AMS), which preferentially fragmented to a carbo-cation at m/z 41, C3H5(+). Quantum chemical calculations (DFT with the M062X functional 6-31G(d,p) basis sets) for the fragmentation reaction pathways of AMS indicated that the most stable protonated AMS cation at m/z 89 is a protonated (cyclic) thiirane, and that the fragmentation reaction pathways of AMS in the drift tube are kinetically controlled. The protonated parent ion MH(+) is the predominant product in PTR-MS, except for diethyl disulfide at high collisional energies. The saturated monosulfides R-S-R' (with R<R') have little or no fragmentation, at the same time the most abundant fragment ion is the smaller R-S(+) fragment. The saturated disulfides R-S-S-R display more fragmentation than the saturated monosulfides, the most common fragments are disulfide containing fragments or long-chain carbo-cations. The results rationalize fragmentation data for saturated monosulfides and disulfides and represent a detailed analysis of the fragmentation of an unsaturated sulfide. Apart from the theoretical interest, the results are in support of the quantitative analysis of sulfides with PTR-MS, all the more so as PTR-MS is one of a few techniques that allow for ultra-low quantitative analysis of sulfides.
authors.affiliation: Institut für Ionenphysik und Angewandte Physik, Leopold Franzens Universität Innsbruck, Technikerstr. 25, A-6020, Innsbruck, Austria.
authors.forename: Erna
authors.initials: E
authors.lastname: Schuhfried
authors.forename: Michael
authors.initials: M
authors.lastname: Probst
authors.forename: Jumras
authors.initials: J
authors.lastname: Limtrakul
authors.forename: Sippakorn
authors.initials: S
authors.lastname: Wannakao
authors.forename: Eugenio
authors.initials: E
authors.lastname: Aprea
authors.forename: Luca
authors.initials: L
authors.lastname: Cappellin
authors.forename: Tilmann D
authors.initials: TD
authors.lastname: Märk
authors.forename: Flavia
authors.initials: F
authors.lastname: Gasperi
authors.forename: Franco
authors.initials: F
authors.lastname: Biasioli