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

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 alfa-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