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Characterisation and proposed origin of mass spectrometric ions observed 30 Th above the ionised molecules of per‐ O ‐methylated carbohydrates
Author(s) -
Robinson Sarah,
Routledge Anne,
ThomasOates Jane
Publication year - 2005
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.2246
Subject(s) - chemistry , reagent , methyl iodide , mass spectrometry , molecule , alkylation , fragmentation (computing) , mass spectrum , ether , carbohydrate , moiety , ion , iodide , tandem mass spectrometry , fast atom bombardment , medicinal chemistry , organic chemistry , chromatography , catalysis , computer science , operating system
Derivatisation of carbohydrates by permethylation significantly improves the mass spectrometric intensity of carbohydrate‐derived ions and allows more readily interpretable fragmentation; in addition, samples are conveniently separated from salts, and larger oligosaccharides are more readily ionised. It has previously been recognised that, in the mass spectra of permethylated carbohydrates, a series of ions indicating species 30 Da larger than the fully methylated carbohydrate molecules are also observed. These species have not been characterised in the literature despite their apparently ubiquitous occurrence in the mass spectra of permethylated carbohydrates. Tandem mass spectrometry (MS/MS) experiments were performed on permethylated carbohydrates and reduced permethylated carbohydrates that exhibit the artefact, demonstrating that the artefact is not reducing terminal specific, and that the artefact can be introduced at any hydroxyl residue. It was further demonstrated through the use of different alkylation reagents that the origin of this artefact group is the alkylating reagent itself. It is proposed that side reactions that occur between the permethylation reagents allow the production of small amounts of iodomethyl methyl ether. This reagent can then compete with methyl iodide for reaction with the carbohydrate OH groups. The result is partial incorporation of a methoxymethyl moiety instead of a methyl group, detected as ‘+30’ artefact ions. Copyright © 2005 John Wiley & Sons, Ltd.