Anion dopant for oligosaccharides in matrix-assisted laser desorption/ionization mass spectrometry

A new anion dopant for oligosaccharides is developed for use in matrix-assi sted laser desorption/ionization mass spectrometry. Two types of sulfate-at tached quasimolecular ions are formed in the negative ion mode when neutral oligosaccharides are doped with dilute H2SO4 solutions. Under mild conditi ons, i.e., low H2SO4 concentration (similar to 10(-3) M) and threshold lase r fluence, a sulfate adduct [M + HSO4](-) is formed. With more concentrated H2SO4 solutions (similar to 10(-2) M) and higher laser fluence, in situ de rivatization of the oligosaccharides occurs to produce an ion whose m/z cor responds to a sulfate derivative [M + HSO4 - H2O](-). Hydrogen sulfate appe ars to be a general anion dopant because it forms complexes with a wide var iety of neutral oligosaccharides. Conversely, anionic oligosaccharides form neither the adduct nor the derivative. The combination of complex formatio n (with neutral oligosaccharides) and the deprotonation of acidic oligosacc harides allows simultaneous detection of the respective mixture.