Glycan functions are usually determined by the structures of the oligosaccharides, which are covalently attached to proteins primarily at 2 structural motifs: the amide group of an asparagine (N-glycans) or the hydroxyl group on serine or threonine (O-glycans). Because of the diversity of the oligosaccharides, even glycosylation at a single site can generate considerable heterogeneity of the mass and charge of glycoproteins. Although different approaches for N-glycans analysis have been described, usually these methods are based on enzymatic release of N-glycans from the protein by PNGase F, and derivation of released glycans, due to the lack of intrinsic chromophores, with a fluorescent labelling before analysis.