Before mass spectrometry analysis, N-glycans must be released from glycoproteins, usually followed by N-glycan derivatization. Derivatization improves sensitivity in mass spectrometry, ionization efficiency and protects functional groups. A lot of isomers cannot be distinguished by mass spectrometry analysis, therefore coupling with separation technique is needed to separate isomers. Matrix-assisted laser desorption/ionization and electrospray ionization are most common ionization modes, which cause little fragmentation or none at all. Molecular mass of analyte can be determined from mass spectrum. N-glycan structural information can be provided by ion fragments in tandem mass spectrum. Isobaric compounds can be differentiated by high-resolution mass spectrometry. N-glycans can be detected by other detection techniques as well, but accurate molecular mass and structural information can be provided by mass spectrometry only.
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