A reliable LC–MS/MS method for the quantification of five bioactive saponins of crude and processed Bupleurum scorzonerifolium in rat plasma and its application to a pharmacokinetic study

A simple and reliable liquid chromatography–mass spectrometry (LC–MS) method was developed for simultaneous determination of saikosaponin A, saikosaponin B 1 , saikosaponin C, saikosaponin D and saikosaponin F in rat plasma using glycyrrhetinic acid as an internal standard (IS). The separation was operated on a Waters BEH C 18 column. The mobile phases of gradient elution consisted of acetonitrile (A) and 0.1% aqueous acetic acid (B). The mass spectrometric detection was accomplished in multiple reaction monitoring mode. The five saponins displayed good linearity ( r 2  > 0.9996). The lower limits of quantitation of saikosaponin A, saikosaponin B 1 , saikosaponin C, saikosaponin D and saikosaponin F were determined to be 2.9, 2.3, 3.5, 2.9 and 3.1 ng/mL, respectively. Moreover, the intra‐ and inter‐day precisions of the five saponins showed an RSD within 2.96%, whereas the accuracy (RE) ranged from −2.28 to 2.78%. Finally, the developed method was fully validated and applied to a comparative pharmacokinetic study of the five bioactive saponins in rats following oral administration of crude and vinegar‐processed Bupleurum scorzonerifolium .