Quantitation of paclitaxel and its two major metabolites using a liquid chromatography–electrospray ionization tandem mass spectrometry

A sensitive and selective liquid chromatographic–tandem mass spectrometric (LC–MS/MS) method for the determination of paclitaxel (Taxol) and its two major metabolites in human plasma has been developed. Samples were prepared after liquid–liquid extraction and analyzed on a C 18 column interfaced with a Q-Trap tandem mass spectrometer. Positive electrospray ionization was employed as the ionization source. The mobile phase consisted of acetonitrile–water (0.05% formic acid) (65:35) at the flow rate of 0.25 mL/min. The analytes and internal standard docetaxel were both detected by use of multiple reaction monitoring mode. The method was linear in the concentration range of 0.5–500.0 ng/mL for paclitaxel, 6α-hydroxypaclitaxel and p-3′-hydroxypaclitaxel, respectively. The lower limit of quantification (LLOQ) was 0.5 ng/mL for paclitaxel, 6α-hydroxypaclitaxel and p-3′-hydroxypaclitaxel, respectively. The intra- and inter-day relative standard deviation across three validation runs over the entire concentration range was less than 8.18%. The accuracy determined at three concentrations was within ±10.8% in terms of relative error. The total run time was 7.0 min. This assay offers advantages in terms of expediency, and suitability for the analysis of paclitaxel and its metabolites in various biological fluids.