Regio-isomeric effects in tandem mass spectra of sulfonium cations generated from thiacyclane based sulfonium salts under soft ionization conditions

Abstract

The influence of regio-isomerism of even-electron sulfonium ions on tandem electrospray and matrix-assisted laser desorption/ionization mass spectra recorded by using collision-induced dissociation was investigated. The initial organic sulfides belonged to isomeric thiabicyclane series (substituted 7- and 8-thiabicyclo[4.3.0]nonanes, 2- and 3-thiabicyclo[4.4.0]decanes) and phenylthiolanes. To investigate by the abovementioned mass spectrometry methods, the sulfides were preliminary S-alkylated by methyl, ethyl iodides, their deuterated analogs and trialkoxonium tetrafluoroborates to form corresponding sulfonium salts. The latter salts readily gave off corresponding sulfonium cations under abovementioned desorption/ionization conditions and these cations were precursor ions in collision-induced dissociation experiments. The main quantitative and frequently qualitative differences between collision-induced dissociation spectra of isomers were manifested in mass numbers and relative intensities of the ions Alk-S= CHR (formal structure) that originated from the destruction of sulfur-containing ring. Corresponding peaks are particularly abundant for cations Alk-S= CH and their intensities are usually greater than for other C-substituted homologues. Qualitative difference between fragmentation features of 2- and 3-phenylthiolanium cations is that only the latter can eliminate neutral CHS molecule.

The Use of Polydialkylsiloxanes/Triflic Acid as Derivatization Agents in the Analysis of Sulfur-Containing Aromatics by “Soft”-Ionization Mass Spectrometry

“…To increase the detectability of such compounds, preliminary modifications of targeted sulfur atoms appeared to be promising approaches, among which fixed-charge [ 15 ] and charge-generation derivatization are particularly efficient [ 16 ]. The simplest version of such reactions includes the interaction of dialkyl sulfides, saturated cyclic sulfides and mercaptans with alkyl halides or trialkyloxonium tetrafluoroborates that proceeds under mild conditions giving rise to sulfonium salts with a quantitative yield [ 17 ].…”

An approach to analysis of primary amines by a combination of thin‐layer chromatography and matrix‐assisted laser desorption ionization mass spectrometry in conjunction with post‐chromatographic derivatization

“…However, in our opinion, the most attractive approaches utilize the reagents already having permanent covalently‐bonded fixed charge in their structures . Some other promising reactions are based on the charge generation principles . Both latter derivatization reactions give rise to the formation of highly polar salt‐like derivatives possessing a ready charge which provides very efficient desorption/ionization under MALDI conditions.…”