Laser desorption/fourier-transform mass spectrometry for the study of nucleosides, oligosaccharides, and glycosides

Laser desorption/Fourier-transform mass spectrometry (l.d./F.t.m.s.) has been used to investigate the feasibility of desorbing nucleosides, oligosaccharides, and glycosides into the gas phase. Nucleosides were desorbed as (M - H)^- ions or as (M + H)⁺ or more readily as alkali metal ion cationized species. Monosaccharides also could be desorbed as (M - H)^- but not di- or tri-saccharides. At higher laser irradiance, very abundant cationized oligosaccharides were observed. This was particularly true when the Nd:YAG laser was operated in a non-Q-switched mode to give a longer lasting laser pulse. Ions of non-reducing sugars cleaved at the glycosidic bond, but those of reudcing sugars underwent ring cleavage reactions. Various glycosides including quercitrin, rutin, xanthorhammin, digoxin, digitoxin, and erythromycin were also successfully desorbed as cationized species by using l.d./F.t.m.s. Digoxin and digitoxin (M + Na)⁺ ions fragment differently than the (M + H)⁺ ions, presumably because the sodium ion is primarily affiliated with the sugar moiety whereas H⁺ is bound on the steroid portion of the molecule.