Studies on negative electrospray ionization mass spectrometry on saponins

Two kinds of saponins have been investigated by negative electrospray ioniz ation (NESI) mass spectrometry. Under ESI conditions, the [M - H](-) ions o f saponins were observed which provide the molecular weights of saponins. T he fragment pathways of [M - H](-) ions of these two saponins depend on the ir structures. For steroidic saponins, [M - H](-) ion only produces the fra gment ions by the losses of sugar units. For oleanolic saponins, [M - H](-) ion yields the cross-ring ions as well as the fragment ions by the losses of sugar units. Moreover, the abundance of the former is higher than that o f the latter. The characteristic fragments are used to provide the sequence and some linkage information of sugar moieties of saponins. Especially, th eir fragment difference strongly depends on the linkage between the aglycon e and the sugar moieties.