A fragmentation study of an isoflavone glycoside, genistein-7-O-glucoside, using electrospray quadrupole time-of-flight mass spectrometry at high mass resolution

A mass spectrometric method based on the combined use of electrospray ionization, collision-induced dissociation and tandem mass spectrometry at high mass resolution has been applied to an investigation of the structural characterization of genistein-7-O-beta-D-glucoside (5,7,4'-trihydroxyisoflavone). The product ion mass spectrum of [M - H](-) ions shows neutral losses of the glycan residue (162 Da) and of the glycan residue + H-. (163 Da) by rearrangement and scission, respectively, where the latter loss dominates at higher collision energies. The genistein moiety remained intact and only minor fragmentation of the glucose moiety was observed. The low-energy product ion mass spectrum of [M + H](+) ions shows extensive fragmentation of the glucose moiety, though at low ion signal intensity, loss of the glycan residue, and simple fragmentation of the genistein moiety that permits characterization of the substituents in the A and B rings. The use of elevated cone voltages permitted observation of product ion mass spectra of selected primary fragment ions. Product ion mass spectra examined at high mass resolution allowed unambiguous determination of the elemental composition of fragment ions. Fragmentation mechanisms and ion structures have been proposed. (C) 2004 Elsevier B.V. All rights reserved.