Simultaneous determination of imperatorin and its metabolite xanthotoxol in rat plasma and urine by LC-MS/MS and its application to pharmacokinetic studies

An accurate, precise, selective, and sensitive liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) method was developed for the simultaneous determination of imperatorin (IMP) and its metabolite, xanthotoxol (XAN), in rat plasma and urine samples. The analytes, along with psoralen as an internal standard, were determined by multiple reaction monitoring (MRM) operated in the positive electrospray ionization (ESI) mode. Chromatographic separation was performed on an Acquity UPLC BEH C18 column (50 mm × 2.1 mm, 1.7 μm) with a mobile phase consisting of 0.1% formic acid solution and 0.1% formic acid in methanol at a flow rate of 0.3 mL/min. The run time was 6 min per sample and the injection volume was 5 μL. The method had a lower limit of quantification (LLOQ) of 0.25 ng/mL for IMP in plasma and urine, and 1 ng/mL for XAN in urine. The linear calibration curves were fitted over the range of 0.25-1000 ng/mL for IMP in plasma, 0.25-1000 ng/mL for IMP in urine, and 1-1000 ng/mL for XAN in urine, with correlation coefficients greater than 0.995. The inter- and intra-day accuracies (relative error, RE%) were between −8.5% and 3.5%, and the precisions (relative standard deviation, RSD%) were less than 10.0% for all quality control samples (QCs). The analytes were extracted from rat plasma and urine samples using a liquid-liquid extraction method with the extraction recovery in the range of 60.3-79.1%. A good stability of the analytes was observed in all the analysis procedures. The method was successfully validated and applied to determine the pharmacokinetics of IMP in rat plasma and, for the first time, the metabolite kinetics of IMP to XAN in rat urine after IMP administration.