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](-•) 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](-•) ions. In addition, the characteristic ion [Y(0)-2H](-) was observed in the product ion spectrum of genistein 7-O-β-D-glucoside and was also detected, together with the [Y(0)-CH(3)](-•) and [Y(0)-H-CH(3)](-) ions in the product ion spectra of glycitin and 6-methoxy genistein 7-O-β-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.