A study of characteristic fragmentation of isoflavonoids by using negative ion ESI-MSn

Isoflavone mono-O-glycosides were investigated by electrospray ionization tandem mass spectrometry with a quadrupole linear ion trap mass spectrometer in negative ion mode. Isoflavonoids having different positions of glycosylation or methylation were differentiated according to the relative abundances of Y-0(-) and [Y-0 - H](-center dot) ions generated from the [M H](-) ion. It is found that the site of glycosyl or methyl group significantly affects relative abundances of the Y-0(-) and [Y-0 - H](-center dot) ions. In addition, the characteristic ion [Y-0 - 2H](-) was observed in the product ion spectrum of genistein 7-O-beta-D-glucoside and was also detected, together with the [Y-0 - CH3](-center dot) and [Y-0 - H - CH3](-) ions in the product ion spectra of glycitin and 6-methoxy genistein 7-O-beta-D-glucoside. The structures of isoflavonoids can be characterized and identified according to the formation of these diagnostic ions. The results obtained from this investigation can promote the rapid identification of isoflavonoids in crude plant extracts. Copyright (C) 2010 John Wiley & Sons, Ltd.