Ultra-sensitive quantification of paclitaxel using selective solid-phase extraction in conjunction with reversed-phase capillary liquid chromatography/tandem mass spectrometry

The ability to quantify ultra-low concentrations of biologically active compounds in biological matrices is essential for the study of pharmacological/toxicological effects occurring at low doses. Selective solid-phase extraction (SPE) was combined with highly sensitive capillary LC (μLC)–MS/MS analysis to achieve ultra-sensitive quantification of the anti-cancer drug paclitaxel in cancer cells. The optimized SPE selectively extracted paclitaxel and eliminated undesirable matrix compounds, thus enabling a high sample loading volume on the μLC column without compromising chromatographic performance and operational robustness. The validated lower limit of quantification (LOQ) was 5 pg/mL, approx. 20-fold more sensitive than published LC–MS/MS methods. The calibration curve was linear over the range of 5–6250 pg/mL. Accuracy was 98–109% and the variation (CV%) was 2.3–7.4%. This method was applied successfully to quantify temporal drug accumulation by A121a ovarian cancer cells treated with sub-ng/mL concentrations of paclitaxel.