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This study shows that fast atom bombardment (FAB) in combination with collisional activation and tandem mass spectrometric techniques is useful for the characterization of, and the differentiation between, O-diglycosyl, O-C-diglycosyl and di-C-glycosyl flavonoids. A quick differentiation between the three types of glycosyl flavonoids is possible by simply examining FAB mass spectra. Low-energy product ion spectra of [M+H]+ ions have been used for determining the carbohydrate sequence in O-diglycosyl flavonoids and characterizing the terminal monosaccharide in O-C-diglycosyl flavonoids. The data obtained for per-O-deuterated precursor ion species of O-diglycosyl flavonoids indicate that O-linked hydrogen atoms are involved in the formation of Yn+ ions. High-energy product ion spectra of [M+H]+ ions enable further characterization and differentiation of isomeric di-6,8-C-glycosides.

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Current literature data show that flavonoid glycosides are structurally characterized by both positive and negative ion FABMS and that in the case of positive ion FABMS most authors mainly report the presence of (M + Na)' ions. In the frame of our activities on the structure elucidation of biologically active plant metabolites isolated from traditional African medicinal drugs, we regularly have to analyze relatively polar flavonoid glycosides containing one to three carbohydrate units. These products are isolated using common phytochemical separation methods, such as column chromatography on silicagel or Sephadex LH-20. Due to the high salt content of these samples, positive ion FABMS generally results in weak (M + H)' signals, intense (M + Na)' signals and even di-and trisodiated molecular ion species, whereas negative ion FABMS often yields weak (M -H) signals. In order to obtain