Application of ESI/MS, CID/MS and tandem MS/MS to the fragmentation study of eriodictyol 7-O-glucosyl-(1→2)-glucoside and luteolin 7-O-glucosyl-(1→2)-glucoside

A mass spectrometric method based on the combined use of positive and negative electrospray ionization, collision-induced dissociation and tandem mass spectrometry has been applied to the structural characterization of the eriodictyol 7-O-glucosyl-(1 -> 2)-glucoside and luteolin 7-O-glucosyl-(1 -> 2)-glucoside. The low-energy product ion mass spectrum of [M + H](+) and [M - H](-) ions showed extensive fragmentation of the diglucose moiety, loss of the glycan residue, and fragmentation of the aglycon units that permit characterization of the interglycosidic linkage and the substituents in the A- and B-rings. Both glycosides were shown to yield the (X0X1)-X-0.2-X-0.2, ion which can be considered as characteristic of the 1 -> 2 interglycosidic linkage in the glucoglucoside adducts, since it can not be formed in the case of other interglycosidic types. In the case of the eriodictyol diglucoside the 1, 3 fragmentation of the C-ring was observed before those involving the carbohydrates thus allowing the position determination of the diglucoside moiety on the A-ring. In the negative ion mode only the luteolin diglucoside was shown to undergo collision-induced homolytic and heterolytic cleavages of the O-glycosidic bond producing the aglycone radical-anion [Y-0-H](center dot-) and Y-0(-) product ions, while this was not observed in the case of eriodictyol glycoside. CID MS/MS analysis of the sodiated molecules gave complementary informations for the structural characterization of the studied compounds. The B-2(+) fragment which is useful for establishing that the terminal carbohydrate unit is linked to another carbohydrate and not directly to the aglycone was obtained as base peak. This result is of analytical value for the differentiation of O-diglycosyl and di-O-glycosyl flavonoids. (c) 2005 Elsevier B.V. All rights reserved.