Electrospray ionization mass spectrometry of low-molecular-mass S-nitroso compounds and their thiols.

Low-molecular-mass S-nitroso compounds (R-S-N=O) are potent vasodilators and inhibitors of platelet aggregation. This work describes the electrospray ionization mass spectrometric (ESI-MS) analysis of physiological and synthetic low-molecular-mass S-nitroso compounds and their thiols including S-nitrosoglutathione, S-nitrosocysteine, glutathione and cysteine. Mass spectra of the unlabeled and S-15N-labeled low-molecular-mass S-nitroso compounds investigated are characterized by abundant cations due to [M+H]+, [M+Na]+, [(M+H)-NO]+, [2 M+H]+, and [(2 M+H)-2NO]+. Mass spectra of low-molecular-mass thiols are characterized by abundant cations due to [M+H]+, [M+Na]+ and [2M+H]+. Using off-line electrospray ionization tandem mass spectrometry we unequivocally identified S-[15N]nitrosoglutathione in human red blood cells formed after their incubation with S-[15N]nitrosocysteine. These results suggest that ESI-MS in combination with an appropriate liquid chromatographic system should be a useful analytical approach for the on-line quantitative determination of low-molecular-mass S-nitroso compounds in biological fluids in the presence of their thiols and nitrite. Considerations were made about on-line ESI-MS and quantitative measurements.