Glycosylation mainly refers to the enzymatic process that attaches glycans to proteins, lipids, or other organic molecules. It is the most common protein post-translational modifications (PTM). Glycosylation analysis is very challenging because of the complexity and the isobaric nature of attached glycans. With the increasing application of protein therapeutics, such as monoclone antibodies, glycoproteins, hormones, cytokines and clotting factors in clinical practice, routinely monitoring the N-glycosylation of proteins is becoming more and more popular.