32] Linkage positions in glycoconjugates by periodate oxidation and fast atom bombardment mass spectrometry

Abstract

This chapter discusses linkage positions in glycoconjugates by periodate oxidation and fast atom bombardment mass spectrometry (FAB-MS). The introduction of fast atom bombardment mass spectrometry started a new era in mass spectrometry. Biological compounds like peptides and underivatized glycoconjugates that cannot be analyzed by the conventional electron ionization mass spectrometry could be analyzed using this technique. In contrast to electron ionization, the ionization in FAB is not dependent on volatility because compounds are ionized in solution by a fast atom beam of argon or xenon. FAB-MS of underivatized glycoconjugates gives information about the molecular weight, but fragment ions formed by cleavage are of low abundance. In electron ionization mass spectrometry of permethylated glycoconjugates, the sequence ions, from the nonreducing terminal, are formed by ionization of the ring oxygen followed by a homolytic cleavage of the glycosidic bonds. The products formed after periodate oxidation depend on position of substitution and the linkages between the monosaccharide residues are deduced from the primary and secondary sequence ions.