Simultaneous determination of pethidine and norpethidine in mouse plasma by liquid chromatography-electrospray ionization source-mass spectrometry.

This study aims to develop an analytical method for the simultaneous determination of pethidine and norpethidine in mouse plasma using the liquid chromatography-electrospray ionization source-tandem mass spectrometry (LC-ESI-MS-MS) method. After being alkalified, the plasma specimens were extracted by liquid-liquid extraction with ethyl acetate. Chromatographic separation was performed on a C18 column (150 × 2.1 mm internal diameter, 5 μm) using a mobile phase consisting of acetonitrile/water (5 mM ammonium acetate in water, pH 6.2, 40:60, v/v) during a total run time of 4.0 min. The mass spectrometer was operated under the positive ionization mode. The multiple reaction monitoring with the transitions of m/z 248.1 → 174.2, 234.2 → 160.0 and 389.2 → 201.1 was used to quantify pethidine, norpethidine and cetirizine (internal standard), respectively. Linear calibration curves were obtained over concentration ranges of 8.24-8,440.00 ng/mL for pethidine, and 6.15-6,300.00 ng/mL for norpethidine. The intra- and interday precisions and accuracies were <15% (relative standard deviations, RSDs), and the accuracies were within the interval of 94-103% for both. The lower limits of quantification in mouse plasma were 8.24 ng/mL for pethidine and 6.15 ng/mL for norpethidine. Subsequently, the validated method was successfully applied to a pharmacokinetics study of pethidine and its metabolite, norpethidine, in mice.