Atmospheric Pressure Spray and Electrospray Mass Spectra of Glycine and Its Oligopeptides

Abstract

Mass spectra of glycine, glycyl-glycine and glycyl-glycyl-glycine obtained by atmospheric pressure spray mass spectrometry (APS-MS) are compared with those obtained by electrospray mass spectrometry (ESP-MS). Intense cationized molecules of (M+Na)+ and (M+K)+ are observed in addition to protonated molecules of (M+H)+ in the atmospheric pressure spray mass spectra, while only protonated molecules are observed in the electrospray mass spectra. This result clearly indicates that the two methods differ greatly as regards ionization process, although sample solutions are sprayed to produce ions under atmospheric pressure in both methods.