Evaluation of quadrupole time-of-flight tandem mass spectrometry and ion-trap multiple-stage mass spectrometry for the differentiation of C-glycosidic flavonoid isomers

LC–MS–MS is becoming a very important tool for the on-line identification of natural products in crude plant extracts. For an efficient use of this technique in the dereplication of natural products, a careful study of the parameters used to generate informative MS–MS spectra is needed. In this paper, the collision-induced dissociation (CID) MS–MS spectra of ubiquitous C-glycosidic flavonoids have been systematically studied using hybrid quadrupole time-of-flight and ion-trap (IT) mass analysers under various CID energy conditions. Efficient differentiation of flavonoid C-glycoside isomers was possible, based on the comparison of CID-MS–MS spectra of particular C-glycoside unit fragments. Striking differences between 6-C and 8-C flavonoid glycosides were especially observed in the product ion spectra of their 0,2X+ fragments ([M+H-120]+). Some guidelines for the on-line characterisation of C-glycosidic flavonoids by LC–MS–MS or LC–multiple-stage MS are given.