Abstract: The transformation rules of saikosaponin a and saikosaponin d under different extraction methods were studied by ultra-performance liquid chromatography coupled with Quadrupole-time of flight mass spectrometry (UPLC-QTof-MS).A new UPLC-QTof-MS method was developed for profiling and quantification of the transformation products of saikosaponin a and saikosaponin d under different extraction methods.Chromatographic separation was performed on an Acquity UPLC BEH C₁₈ column (2.1 mm×50 mm,1.7 μm) with a mobile phase consisting of acetonitrile (A) and 0.01% formic acid in water (B).The flow rate was kept constant at 0.45 mL/min with a gradient elution.QTof-MS was used as the detector.Twelve samples of Radix Bupleuri were individually extracted using 12 different extraction methods and were then analyzed by UPLC-QTof-MS with negative ion mode.The transformation rule of saikosaponin a and saikosaponin d under different extraction methods were derived:saikosaponin a and saikosaponin d were hydrolyzed into saikosaponin b₁ and saikosaponin b₂ under acidic condition at at room temperature.The glycosidic bond was hydrolyzed yielded to sapogenin under acid condition and being heated.Saikosaponin a and saikosaponin d were stable under neutral and alkaline condition.The experimental results provided a refrence for extraction,separation and analysis of saikosaponin a and saikosaponin d.

Key words: UPLC-QTof-MS, saikosaponin a, saikosaponin d, saikosaponin b₁, saikosaponin b₂, extraction