Differentiation and identification of ginsenoside isomers by electrospray ionization tandem mass spectrometry

Three pairs of ginsenoside isomers (R-g2 and R-g3, R-g1 and F-l1 as well as R-d and R-e) were differentiated and identified through accurate mass measurement of mass spectrometry (MS) and MS-MS. [M + Li](+) and [M - H]- ions were detected in full-scan MS analyses and selected for the MS-MS experiments using positive and negative ion electrospray ionizations (ESI), respectively. The structures of aglycone and alpha- and beta-saccharide sugars in various ginsenosides were determined from the spectrum interpretation and accurate mass measurement. Z and C type ions were predominantly observed in the MS-MS spectra of [M + Li](+) ions, while Y type ions were the most abundant ions in the spectra obtained from, the negative ion mode analysis. Furthermore, X and A ions resulted from cross-ring cleavage on the sugar directly connected to aglycone were detected in both positive and negative ion spectra, which provided the site information of the saccharide chains. The obtained MS-MS profiles were used for the structural confirmation of ginsenoside R-g2 collected from column chromatography separation of a Chinese Panax ginseng extract. The ESI-MS data with accurate mass assignment suggested that a co-eluted ginsenoside also existed in the sample fraction. The interpretation of its MS-MS spectrum and fragmentation pathways allowed the detection of the ginsenoside R-f, differentiating from its isomers R-g1 and F-l1. (c) 2004 Elsevier B.V. All rights reserved.