A novel detection method for quaternization of amino acid and peptide was reported. In this method Ag 2CO 3 was employed instead of KHCO 3 to catalyze the occurrence of quaternization reaction. The absence of metal ions in the reaction system enabled us to in situ detect the quaternizing products by using electrospray ionization mass spectrometry(ESI-MS). We analyzed quaternizing products of six amino acids and two peptides in situ, and obtained the ratio of major product to by-product, which suggests the new method possesses prominent advantages over the old one. This method could offer a potential chance to combine quaternization with mass spectrometry which is helpful for the future use of quaternization reaction in quantitative proteomics.
