Simultaneous LC–MS Analysis of Paclitaxel and Retinoic Acid in Plasma and Tissues from Tumor-Bearing Mice

Abstract

A novel method has been developed for simultaneous analysis of paclitaxel (PTX) and retinoic acid (ATRA) in mice plasma and tissue homogenates. The analyte was isolated by liquid–liquid partitioning, to minimize analyte degradation, and fractions were analyzed by liquid chromatography–mass spectrometry (LC–MS). Liquid–liquid extraction with tert-butyl methyl ether was used for sample preparation and docetaxel was used as internal standard (IS). Separation of PTX, ATRA, and the IS was performed on a C₁₈ column with gradient elution and detection by use of a single-quadrupole mass spectrometer in selected-ion-monitoring mode. The method had high extraction recovery (>85%) and accuracy (>90%), with intra-day and inter-day precision <15%, and was rugged with good linearity. The limits of quantitation were determined to be 2 and 4 ng mL⁻¹ for PTX and ATRA, respectively. Freeze–thaw stability, short-term stability, long-term stability, and sample stability in the autosampler tray were examined; this indicated freezing and thawing during bio-sample preparation should be avoided, but no other stability-related problems occurred during sample storage, extraction, and chromatography of PTX and ATRA in plasma and tissue samples. The assay was successfully used for simultaneous analysis of PTX and ATRA in mice plasma and different tissues to support pharmacokinetic and in-vivo distribution studies of the two drugs.