Relative determination of the alkaloid metabolites of Er Miao San in rat urine by LC–MS/MS and its application to pharmacokinetics

In the present study, five metabolites of Cortex Phellodendri Chinensis, an important herbal drug, were identified using liquid chromatography multi-stage tandem mass spectrometric techniques (LC–MSn). A sensitive and rapid high-performance liquid chromatographic tandem mass spectrometry (LC–MS/MS) method was developed for the quantitation of the five metabolites, utilizing chlorobenzylidine as the internal standard in rat urine. Urine samples were precipitated with acetonitrile. Chromatographic separation was achieved on a Waters C18 analytical column. Detection was performed by a multiple reaction monitoring (MRM) mode via an electrospray ionization (ESI) source operating in the positive ionization mode. The method was linear over the concentration range of 0.05–1.00c for all components. The intra- and inter-day precision values were less than 14.6% and the deviations ranged from −4.4 to 13.8%. The recoveries at three levels were more than 73.7%. The fully validated method was used to determine the metabolites amount in rat urine to investigate the changes caused by coupling with Atractylodes lancea in Er Miao San preparation on metabolism.