ELECTRON IONIZATION-TANDEM MASS-SPECTROMETRY OF GLYCOSPHINGOLIPIDS .1. THE IDENTIFICATION OF COMPOUND-SPECIFIC SEQUENCE IONS IN THE COLLISION-INDUCED DISSOCIATION SPECTRA OF THE IMMONIUM IONS OF 2 ISOMERIC HEXAGLYCOSYLCERAMIDES

A permethylated-reduced hexaglycosylceramide in a complex glycolipid mixture isolated from a unique human tissue has been identified by using tandem mass spectrometry (MS/MS). The mass spectrum of this glycolipid mixture, obtained by using in-beam electron ionization, is very complex, and fragment ions derived from the hexaglycosylceramide cannot be distinguished from other ions. Tandem mass spectrometry using a four-sector mass spectrometer gave the mass spectrum of the immonium ion of the permethylated-reduced hexaglycosylceramide (m/z 1645.8), which is characteristic of its structure. Comparison of this MS/MS spectrum with those of two similarly derivatized blood group hexaglycosylceramide isomers permitted identification of the unknown glycolipid structure.