ESI-triple quadrupole tandem mass spectrometry (MS/MS) has previously been applied to glycosidic linkage assignment in carbohydrates by combining permethylation with alkali metal cation adduction in positive mode ionization and has provided both sensitivity and extensive glycosidic characterization. However, the linkage identification is often compromised by the presence of N-acetylated amino sugars or sialic acids and by increasing molecular size, factors which tend to promote glycosidic fragmentation over the ring-opening pathways required for linkage identification. Previous investigators have assigned linkages in disaccharides by negative mode ionization and low energy collisions. In this study, linkage analysis by negative mode electrospray ionization (ESI) and triple quadrupole MS/MS is extended to larger oligosaccharides. Linkage identification proceeds by specific eliminations from the reducing end. Although the initial site of deprotonation is not required to b e the reducing terminal, glycosidic linkages of oligosaccharides without a free reducing end cannot generally be determined.
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