The workflow of glycoprotein-based and glycopeptides-based analyses. Briefly, in the glycoprotein-based approach, glycoproteins are enriched first, then digested into peptides and analyzed by mass spectrometry (MS). In the glycopeptide-based approach, proteins are digested enzymatically and/or chemically; then, the peptide mixture is enriched for glycopeptides and identified by MS analysis. SPEG: solid-phase extraction of N-linked glycopeptides).