Simultaneous determination of seven flavonoids in dog plasma by ultra-performance liquid chromatography–tandem mass spectrometry and its application to a bioequivalence study of bioactive components in Herba Epimedii and Er-Xian Decoction

In this study, a sensitive and specific ultra-performance liquid chromatography–tandem mass method has been developed and validated for the identification and determination of 7 flavonoids in dog plasma for the first time: epimedin A, epimedin B, epimedin C, icariin, sagittatoside B, 2″-O-rhamnosyl icariside II, and baohuoside I. Chromatographic separation was accomplished on an Agilent Zorbax-SB C₁₈ column (50 mm × 2.1 mm, 1.8 μm) with a gradient elution system composed of 0.3% acetic acid and 0.3% acetic acid in acetonitrile at a flow rate of 0.4 mL/min. Detection was based on a triple quadrupole mass spectrometer using a multiple reaction monitoring mode with an electrospray ionization source. All of the calibration curves showed good linearity (r > 0.99) within the tested concentration ranges. The lower limits of quantification of the seven analytes were all lower than 0.0654 ng/mL. The relative standard deviations for intra- and inter-batches of the seven analytes were less than 13.7% and 14.9%, respectively, at four concentration levels of quality control samples, and the recoveries were between 92.8% and 114.5%, respectively. In addition, the seven flavonoids were found to be stable in dog plasma samples under short- and long-term storage and processing conditions. The validated method was successfully applied to a bioequivalence study in dog plasma after the oral administration of extracts of Herba Epimedii and Er-Xian Decoction.