Chemical ionization and electron impact mass spectra of oligosaccharides derived from sphingoglycolipids

Chemical ionization (CI) mass spectra with isobutane and ammonia for the oligosaccharides obtained from sphingoglycolipids were compared with their electron impact (EI) mass spectra. The oligosaccahride moieties were liberated from the parent glycolipids and were further reduced with sodium borohydride. They were analyzed as their permethyl peracetyl and pertrimethylsilyl derivatives. In the CI spectra, peaks corresponding to QM+ and/or [M-59]+ were observed in all of the peracetylated oligosaccharides examined. In CI with ammonia as the reagent, H+ was transferred to nitrogen-containing saccharides to produce [MH]+ and NH4 was transferred to nitrogen-free saccharides to yield [M+NH4]+ as QM+. Non-reducing ends yielded very intense peaks in CI spectra. On the other hand, the reduced end, glucitol, produced rather prominent peaks in EI spectra. Fragment ions due to cleavage of glycosidic bonds were major ones under the CI conditions, and they could be used for elucidating the sugar sequence in the oligosaccharides. An additional characteristic feature in the CI spectra was that ions due to scission of hexosaminyl glycosidic linkages were observed with very high intensities.