ELECTROSPRAY-IONIZATION AND COLLISION-INDUCED DISSOCIATION TIME-OF-FLIGHT MASS-SPECTROMETRY OF NEUTRAL GLYCOSPHINGOLIPIDS

A series of native naturally occurring neutral glycosphingolipids has been analysed by electrospray ionization tandem mass spectrometry usin g a hybrid magnetic sector-TOP instrument. The collision-induced disso ciation products of precursor ions were detected by an orthogonal acce leration times-of-flight mass spectrometer as the second analyser. Gly cosphingolipids, with mono-to hexa-saccharide chain lengths with diffe rent ceramide constituents, were studied. The result of electrospray i onization in the positive ion mode generally showed singly charged mol ecular ions with Na+ as adduct, [M+Na](+). The sensitivity of the elec trospray ionization was greatly enhanced by addition of NaCl, LiCl (fo rming [M+Li](+)) or KCl(yielding [M+K](+)) to the sample. A comparison between the collision-iudnced dissociation of precursor molecular ion s of monoglycosylceramides, using Na+, Li+ and K+ as adducting species , showed that the intensity of the fragment ions and the extent of the daughter ion fragmentation of the molecular ions, are dependent on th e type of adduct used. The daughter ion spectra of Li+ adduct ions sho wed intense sequence fragment ions, both of the saccharide chain and t he ceramide moiety, and were superior to those obtained using Na+ or K +. The collision-induced dissociation spectra of the [M+Li](+) ions, o f glycosphingolipids containing di- to hexasaccharides, are also prese nted. Proposed possible fragments, resulting from the CID of the molec ular ions [M+L](+) of monoglycosylceramides, are shown. (C) 1998 John Whey & Sons, Ltd.