Mass spectrometry of hydroxy dicarboxylic acids as trimethylsilyl derivatives. Rearrangement fragmentations

Abstract

Gas chromatography—mass spectrometry offers a convenient method for the separation and identification of hydroxy dicarboxylic acids as open‐chain trimethylsilyl (TMS) derivatives. Mass spectra were studied of aldaric (tartronic, tartaric, pentaric and hexaric) acids and deoxyaldaric (malic, 2‐deoxypentaric, 2‐deoxyhexaric, 3‐deoxypentaric and 3‐deoxyhexaric) acids. The different structural types can be readily identified from their characteristic spectra.The most prominent fragmentations involving the rupture of one bond are the loss of a siliconlinked methyl group and the formation of α‐cleavage ions by carbon chain cleavage. The further decay is characterized by a number of significant rearrangements specific of TMS derivatives. Several of these can be classified as involving migration of a TMS group to an oxygen atom or migration of an ester OTMS group to a silicon atom. Concomitant loss of a stable molecule often provides a driving force.Prominent odd‐electron ions are formed by a McLafferty‐type rearrangement of a TMS group. The decomposition of several even‐electron ions can be regarded as analogous to that rearrangement.