Characterization of ginseng saponins using electrospray mass spectrometry and collision-induced dissociation experiments of metal-attachment ions

Electrospray mass spectrometry (ESMS) and collision-induced dissociation (C ID) methodologies have been developed for the structural characterization o f ginseng saponins (ginsenosides). Ginsenosides are terpene glycosides cont aining a triterpene core to which one to four sugars may be attached. They are neutral molecules which readily form molecular metal-attachment ions in positive ion ESMS experiments. In the presence of ammonium hydroxide inten se deprotonated ions are generated. Both positive and negative ion ESMS exp eriments were found to be useful for molecular mass and structure determina tion of ten ginsenoside standards. Negative ion experiments made possible t he determination of the molecular mass of each ginsenoside standard, the ma ss of the triterpene core and the masses and sequences of the sugar residue s. Positive ton ESMS experiments with the alkali metal cations Li+ or Na+ a nd the transition metal cations Co2+, Ni2+ and Zn2+ were also useful in det ermining molecular masses. These alkali and transition metal cations form s trongly bonded attachment ions with the ginsenosides. As a result, the CID mass spectra of the metal attachment ions show a variety of (structure char acteristic) fragmentations. These experiments can be used to determine the identity of the triterpene core, the types and attachment points of sugars to the core and the nature of the O-glycosidic linkages in the appended dis accharides. Combining the results from the negative and positive ion experi ments provides a promising approach to the structure analysis of this class of natural products.