A novel catalytic application of heteropolyacids： chemical transformation of major ginsenosides into rare ginsenosides exemplified by R_（g1）

High performance liquid chromatography coupled with quadruple-time-of-flight mass spectrometry（HPLC-Q-TOF-MS）method was developed for analyzing the hydrolytic mixtures of ginsenoside R_（g1） in acidic conditions（pH 3）. Three catalysts, a heteropolyacid（H_4SiW_（12）O_（40）, SiW_（12） for short）, its complex with γ-CD（SiW_（12）/γ-CD for short） and formic acid, were used for comparison. The chemical transformation products were identified based on the accurate mass measurement and the fragment ions obtained from tandem mass spectrometry. It was concluded that the catalytic efficiency of SiW_（12）（≈SiW_（12）/γ-CD） is ca. 410 times higher than that of formic acid, thus becoming the most efficient catalyst for chemical transformations of ginsenosides.