We explained a simple method of determining the molecuar weigh of a pure glycolside. the method was based on the law that when glycosides were mixed with alali metal ions only the adduct lons of molecule with alkali metal ions appeard in the high mass region of their fast atom bombardmetn mass spectra.in the same way when a mixture of glycosides was mixed with an appropriate amount of Na+ and Li+ pairs of strong peaks appeared in the FAB mass spectra. these adduct ions were easily recognized due to fact that they were very strong and their mass difference was uniue(16u). from these adducts ions, the molecular weitht of each glycoside inthe mixture may be determined. this technique has not been reported previously.

Key words: MASS SPECTROGRAPHY, FAST ATOM BOMBARDMENT, ALKALI METAL ION