Fragmentation characteristics and isomeric differentiation of flavonol O-rhamnosides using negative ion electrospray ionization tandem mass spectrometry

RATIONALE Flavonoids exhibit a wide range of biological activities. The differentiation and structural characterization of the flavonol O-rhamnosides and their isomers are important research topics. Electrospray ionization tandem mass spectrometry (ESI-MSn) is an indispensable tool and has become an efficient method for the identification of bioactive natural products. METHODS Negative ion ESI-MSn was used to characterize and differentiate flavonol O-rhamnosides and their isomeric compounds. The collision energies in collision-induced dissociation were varied to optimize the structural information. RESULTS Flavonol 7-O-rhamnosides containing either a hydroxyl or a methoxyl group at the C-8 position clearly differed from their isomeric compounds, such as the flavonol 3-O-rhamnosides, in the product ion spectra of the [MH] ions. The differences in the locations of the glycosyl group and OCH3 group resulted in a significant change in the relative abundances of the Y0 and [Y0H] ions, and the formation of some characteristic ions, such as 1,3A0 and [1,3A0CH3]. CONCLUSIONS An efficient ESI-MSn method for the structural identification and isomeric differentiation of flavonol O-rhamnosides was developed. The differences in the glycosyl type, and the glycosylation and methoxylation positions in the structures of isomeric flavonoids, can be determined using ()ESI-MSn spectra. The formation and relative abundances of [Y0H] and Y0 ions, as well as the comparison of some diagnostic ions, are vital in the differentiation of isomeric flavonoids. These results have practical applications in the rapid identification of flavonol O-rhamnosides present in crude bioactive extracts. Copyright (c) 2012 John Wiley & Sons, Ltd.