The neg. ion FAB (NFAB) mass spectra of eight glycosides (saponins) containing one to three sugar units have been studied. On comparison of the mass spectra of NFAB with the corresponding pos. ion FAB (PFAB) spectra, it was shown that the former exhibited a more predominant quasi-mol. ions [M - H]- and thus gave more definite information about mol. wt. of the sample than the latter. Among the three matrix substances tested, glycerol, thioglycerol and polyethylene glycol-200, the last one gave the best results. The collisional activation spectra of the mass selected ion [M - H]-(NFAB-CA) gave a series of characteristic fragments ions which were useful for determination of the sugar sequences of the glycosides. The patterns of the NFAB-CA spectra were more clear than that of the PFAB-CA spectra, thus gave a more definite conclusion about the sequences. Contrary to the PFAB-CA spectra, in which there was usually a strong peak of the aglycon residue ion, in the NFAB-CA spectra, however, such an ion peak was absent. Therefore, for structural anal. of oligoglycosides, it would be better to take both of these two types of mass spectra together.

Key words: MOLECULAR WEIGHT, MASS SPECTROGRAPHY, GLUCOSE, STEROIDS, GLYCOSIDE, STRUCTURAL ANALYSIS, ANION, ION COLLISIONS, RHAMNOSE, FAST ATOM BOMBARDMENT