OLIGOSACCHARIDE CHARACTERIZATION USING COLLISION-INDUCED DISSOCIATION FAST-ATOM-BOMBARDMENT MASS-SPECTROMETRY - EVIDENCE FOR INTERNAL MONOSACCHARIDE RESIDUE LOSS

The protonated and sodium cationized pseudomolecular ions of a series of reducing and non-reducing oligosaccharides possessing aldopentopyranosyl, 6-deoxyaldohexopyranosyl, ketohexofuranosyl, 4-O-methyl glucuronopyranosyl methyl ester and N-acetyl 2-deoxyglucopyranosylamine units were studied using collision-induced dissociation (CID) fast atom bombardment (FAB) mass spectrometry. The CID spectra of the [M + H](+) ions provide information about the sequence of the monosaccharide units, while dissociation of the [M + Na](+) ions by two-bond ring cleavage processes gives rise to fragment ions which allow differentiation of 1 --> 2 and 1 --> 4 linkages, The influence of the structure of the constituent monosaccharides on the dissociation of the [M + H](+) and [M + Na](+) ions is discussed, An unusual type of fragmentation, which we suggest involves the elimination of internal monosaccharides residues, has not only been observed in the FAB mass spectra but also in the unimolecular decomposition and CID spectra of both [M + H](+) ions and oxonium ions from several oligosaccharides containing monosaccharide residues with different masses.