This study described the application of liquid chromatography-tandem mass spectrometry for the quantitation of wogonin and its major metabolite in rat plasma. Only one conjugated metabolite with glucuronic acid was identified by chromatographic and electrospray multi-stage mass spectrometric assay. A derivatization reaction with 2-chlorethanol further demonstrated that the metabolite was wogonin-7 beta-D-glucuronide (W-7-G), not wogonin-5 beta-D-glucuronide. Other conjugated metabolites, e.g., sulfates and glucosides, were not detected. The plasma concentration of free wogonin was determined using atmospheric pressure chemical ionization source in the selected reaction monitoring mode. The method had a lower limit of quantitation of 0.25 ng/ml for wogonin, which offered increased sensitivity, selectivity and speed of analysis over an existing method. Incubation of the plasma samples with beta-glucuronidase allows the quantitation of W-7-G. This quantitation method was successfully applied to a preclinical pharmacokinetic study of wogonin and its major metabolite, W-7-G, after an oral administration of 5 mg/kg wogonin to rats.
Copyright 2002 Elsevier Science BV.