Glycan‐Selective MALDI In‐Source Decay Analysis of Intact Glycoproteins

Abstract A simple matrix‐assisted laser desorption/ionization‐time‐of‐flight (MALDI‐TOF) mass spectrometry (MS) approach has been developed to analyze the structural pattern of glycan on glycoproteins without any digestive or modification pretreatment. For a 7 pmol sample of intact glycoprotein, RNase B, a solid ionic matrix DHB‐aniline‐sodium enabled a regioselective in‐source decay (ISD) and glycan‐selective ionization as a sodium adduct ion, [M+Na] + . This matrix significantly reduced the formation of peptide‐fragment‐derived ions, and a high‐mannose‐type glycan pattern was observed. This ISD product ion was formed by selective cleavage of the reducing end of the glycan by 0,2 A or 2,4 A type cross‐ring cleavage. Pseudo‐MS 3 ‐type post‐source decay (PSD) analysis of an A type ion indicated the regioselectivity of the ISD fragmentation and the glycan sequence. Combining ISD glycomics with conventional ISD proteomics will accelerate quality control for glycoprotein drugs and biomarker discovery.