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As one of the most commonly used medicinal plants,ginseng has been an attractive model herb for study.A wide range of analytical methods has been used to characterize its constituents.However,less effort has been devoted to the rare ginseng saponins,especially their isomers and sugar linkages.In this study,we used segmental monitoring and diagnostic ion filtering to characterize ginseng saponins by rapid liquid chromatography with time-of-flight mass spectrometry (LC-TOF-MS).By using selected diagnostic ions,specific groups of ginseng saponins were readily extracted from the complicated matrix.20? and 20(S) stereo-saponins were differentiated using the peak abundance ratio of [M-H2O+H]+ to [M-2H2O+H]+.The fragmentation behavior of ginsenosides was first reported in negative ion mode by MS/MS with high-energy collision-induced dissociation,producing rules to determine sugar numbers,positions and linkages.Using the rules,we identified and compared the nontarget ginseng saponin profiling of raw and steamed American ginseng roots and berries.We characterized 70 saponins in the samples.Our strategy can be extended to screen and characterize other rare ginseng saponins and their metabolites