Field‐amplified sample injection in capillary zone electrophoresis for the pharmacokinetic research of trace risperidone and its major metabolite 9‐hydroxyrisperidone in beagle dogs

This article describes a method for the simultaneous quantitation of risperidone and its major metabolite, 9‐hydroxyrisperidone, in beagle dog plasma by field‐amplified sample injection in capillary zone electrophoresis. The separation was carried out at 25°C in a 48 cm × 75 µm fused‐silica capillary with an applied voltage of 20 kV using 60 mM NaH₂PO₄ buffer (pH 3.6). The detection wavelength was 280 nm. Clean‐up and preconcentration of plasma samples were conducted by 96‐well formatted liquid‐liquid extraction. In this study, this stacking technique provided a sensitivity enhancement of approximately 158 to 188 fold compared with the same sample without stacking. The method was suitably validated with respect to stability, specificity, linearity, lower limit of quantitation, accuracy, precision, and extraction recovery. Calibration curves exhibited good linearity (r² > 0.995) over a wide concentration range of 2.5 to 200 ng/mL for both risperidone and 9‐hydroxyrisperidone. The intra‐ and interday precisions at the three quality control levels were less than 11.40%. The intra‐ and interday accuracies ranged from 87.90 to 107.17% for risperidone and from 88.43 to 105.92% for 9‐hydroxyrisperidone. All validation data were within the required limits. In conclusion, the method developed was successfully applied to pharmacokinetic studies of risperidone and 9‐hydroxyrisperidone in beagle dogs.