Structural determination of O-glycans by tandem mass spectrometry.

Nano-electrospray ionization quadrupole time-of-flight mass spectrometry (nanoESI-Q-TOF-MS) provides a sensitive means for mapping and sequencing underivatized O-glycans. This chapter describes fragmentation rules of O-glycans by ESI-MS/MS and provides a series of diagnostic ions relevant for the determination of the core type, position, and linkage of fucose, sialic acid, and sulphate residues, as well as information on type I or II chains. Positive-ion mode gives information about core type, linkage, and position of fucose residues. Negative-ion mode can be applied for differentiation between isomeric molecules and for analysis of sulphated or sialylated glycans. The current technology successfully determines the sequence of underivatized oligosaccharides in complex mixtures and provides a significant step toward the goal of characterizing all aspects of carbohydrate structure using a single instrument.