DETAILED CHARACTERIZATION OF CARBOHYDRATE LINKAGE AND SEQUENCE IN AN ION-TRAP MASS-SPECTROMETER - GLYCOSPHINGOLIPIDS

Electrospray ionization with a quadrupole ion trap (qIT) mass analyzer has been utilized to ascertain structural detail obtained with glycoc onjugate samples. In this report, an isomeric disialyl glycosphingolip id sample extracted from human brain tissue was evaluated for sequence , branching, and linkage information. Results were obtained that were qualitatively comparable with triple-quadrupole instruments (Q(1)q(2)Q (3)) with major carbohydrate fragments from C-1-O glycosidic rupture a nd additional fragments that provided a determination of sphingosine a nd N-acyl heterogeneity of the ceramide moiety. In unique contrast, ho wever, the qIT extended carbohydrate understanding through multistep m ass spectrometric (MSn) studies providing for the first time pyran cro ss-ring cleavages that define the interresidue linkage structure for g lycolipids. This was achieved by selecting secondary fragments (MS2) f ree from the energy sinks of facile bond rupture that dominate product ion spectra. Isolation and activation of these substructures result i n a more uniform distribution of fragments, providing structural insig hts previously inaccessible by tandem mass spectrometry. (C) 1998 Acad emic Press.