OLIGOSACCHARIDE CHARACTERIZATION USING COLLISION-INDUCED DISSOCIATIONFAST-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 aldopentopyra nosyl, 6-deoxyaldohexopyranosyl, ketohexofuranosyl, 4-O-methyl glucuro nopyranosyl methyl ester and N-acetyl 2-deoxyglucopyranosylamine units were studied using collision-induced dissociation (CID) fast atom bom bardment (FAB) mass spectrometry. The CID spectra of the [M + H](+) io ns 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 con stituent 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 u nimolecular decomposition and CID spectra of both [M + H](+) ions and oxonium ions from several oligosaccharides containing monosaccharide r esidues with different masses.