Discrimination of isomeric dihydroflavone and chalcone by the boosting optimal collision energy-liquid chromatography-tandem mass spectrometry: A case study of pharmacokinetics in honey-fried licorice

The occurrence of isomeric dihydroflavone and chalcone, two important subfamilies of flavonoid class, extensively happens in herbal medicines. However, identical MS/MS spectra make the identity confirmation a tough job, the complexity will be further boosted in biological samples. Inspired by that isomers possess distinct inherent physicochemical parameters, optimal collision energy (OCE), which is positively correlated with the bond dissociation energies (BDEs), was evaluated towards differentiating isomeric dihydroflavone and chalcone. It was achieved by plotting their relative response-collision energy curves (RRCECs) and comparing the unique OCEs obtained. As a result, difference were observed for either OCE of bond dissociations involving Retro Diels-Alder (RDA) reaction as well as glycosidic cleavage when comparing two pairs of isomers, which were liquiritin vs. isoliquiritin and liquiritigenin vs. isoliquiritigenin, because the energies required for bond dissociation to produce identical fragment ions varies among isomers. Furthermore, OCEs consistently ranked dihydroflavone higher than chalcone, aligning with their BDEs determined through quantum calculation. These results suggested great potential for OCEs in distinguishing between dihydroflavone and chalcone. By applying the discriminating criterion, successful identity recognition was achieved for the two pairs of isomers among the many signals sharing identical MRM transitions in honey-fried licorice treated plasma. Thereafter, the confidence-enhanced OCE-LC-MS/MS method was applied to characterize and determine these 4 isomers along with 3 components of honey-fried licorice in rat plasma, the definite determination as well as the pharmacokinetic courses were subsequently accomplished and discussed. Overall, this study boosted the application of OCE-LC-MS/MS in isomers discrimination of isomeric dihydroflavone and chalcone.