Sulfides: chemical ionization induced fragmentation studied with Proton Transfer Reaction‐Mass Spectrometry and density functional calculations |
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Authors: | Erna Schuhfried Michael Probst Jumras Limtrakul Sippakorn Wannakao Eugenio Aprea Luca Cappellin Tilmann D Märk Flavia Gasperi Franco Biasioli |
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Institution: | 1. Institut für Ionenphysik und Angewandte Physik, Leopold Franzens Universit?t Innsbruck, , A‐6020 Innsbruck, Austria;2. Department of Chemistry and NANOTEC Center for Nanoscale Materials Design for Green Nanotechnology, Kasetsart University Bangkok, , 10900 Thailand;3. IASMA Research Innovation Centre, Fondazione Edmund Mach, Food Quality and Nutrition Department, , 38010 S Michele a/A, TN, Italy |
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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. Copyright © 2013 John Wiley & Sons, Ltd. |
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Keywords: | Proton Transfer Reaction‐Mass Spectrometry sulfide chemical ionization fragmentation density functional theory |
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