Table 1.

Mass Shift of Glycopeptide Modification by Ethyl Esterification and Ethylenediamine (EDA) Amidation. Ethyl Esterification Modifies α2,6-Linked Sialic Acids, While EDA Derivatizes α2,3-Linked Sialic Acids

Group	Modification	Reagent	Mass shift (Da)
2,3-Linked sialic acid	Amidation	EDA	42.058183
2,6-Linked sialic acid	Esterification	Ethanol	28.031301
Aspartic acid (D)	Amidation	EDA	42.058183
	Esterification	Ethanol	28.031301
Glutamic acid (E)	Amidation	EDA	42.058183
	Esterification	Ethanol	28.031301
Protein C-terminal	Esterification	Ethanol	28.031301
	Amidation	EDA	42.058183