Abstract: Disclosed is a method of preparing a sample that is suitably used for analysis of a glycoprotein or glycopeptide. A first reaction is performed to modify or remove at least one primary amino group contained in a peptide moiety of a glycopeptide or glycoprotein. Thereafter, a second reaction is performed. The second reaction is a reaction capable of modifying a carboxy group of sialic acid of a sugar chain. After the second reaction, a derivative from ?2,3-linked sialic acid a derivative from ?2,6-linked sialic acid have different masses. Determination of the presence or absence of sialic acid in the sugar chain of a glycoprotein or glycopeptide and identification of the linkage type of sialic acid can be simply performed by mass spectrometry.

Abstract: In the method of preparing a sample for analysis, a reaction is performed that produces different modified product depending on the sialic acid linkage type when a sialic acid is bound to a sugar chain of an analyte. In this reaction, an analyte containing a sugar chain, an amine containing two or more carbon atoms, and a dehydration-condensation agent are used. The sialic acid linkage type can be identified by analyzing the resulting sample with mass spectrometry etc. This method is applicable not only to free sugar chains but also to glycopeptides and glycoproteins.