Quantitation of catalpol in rat plasma by liquid chromatography/electrospray ionization tandem mass spectrometry and its pharmacokinetic study.

A sensitive, rapid and specific liquid chromatography/tandem mass spectrometry (LC/MS/MS) assay has been established for the quantitation of catalpol in rat plasma. Plasma samples were treated by precipitating protein with methanol and were chromatographed by a Diamonsil C(18) column (150 mm x 4.6 mm I.D., 5 microm) with the mobile phase consisting of methanol and 10 mM ammonium formate (30:70, v/v). The selected reaction monitoring (SRM) transitions were performed at m/z 380.1-->183.0 for catalpol and m/z 364.3-->167.0 for aucubin (IS) in the positive ion mode with electrospray ionization (ESI) source. Calibration curve was linear over the concentration range of 10-20,000 ng/mL. The mean recovery was 76.5+/-5.2% and the matrix effect ranged from -5.1 to 13.0%. The intra- and inter-day precisions were less than 6.3 and 14.6%, respectively, and the accuracy was within +/-5.6%. Catalpol was stable in possible conditions of storing and handling. The validated method has been successfully applied to determine the plasma concentration of catalpol for a pharmacokinetic study of catalpol after oral administration of 50 mg/kg to rats.