Comparison of solid-phase microextraction and liquid-liquid extraction in 96-well format for the determination of a drug compound in human plasma by liquid chromatography with tandem mass spectrometric detection

Two sensitive and selective methods based on solid phase microextraction (SPME) and liquid-liquid extraction (LLE) in 96-well format, in combination with high performance liquid chromatography (HPLC) with tandem mass spectrometric (MS/MS) detection have been developed to determine a model drug compound in human plasma. Both assays were performed on an Applied Biosystems-Sciex API 4000 tandem mass spectrometer interfaced with a turbo ion-spray probe and operated in the negative ionization mode. A lower limit of quantitation (LLOQ) of 1 ng/mL achieved when 0.25 mL of human plasma was processed. In both methods, a stable isotope labeled internal standard was utilized. The methods were validated in the concentration range of 1-500 ng/mL. The intraday precision (%C.V.) of the method using LLE was 0.8% at LLOQ, and was equal to or lower than 3.3% at all other concentrations, while the intraday precision (%C.V.) of the method using SPME was 6.9% at LLOQ, and was equal to or lower than 5.7% at all other concentrations. Based on the direct comparison of the two methods and their successful applications in clinical sample analysis, it may be concluded that SPME may be considered and used as an alternative approach for quantitative determination of drugs in pharmacokinetic studies.