SENSITIVE HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHIC METHOD FOR THE DETERMINATION OF LABETALOL DIASTEREOISOMERS IN PLASMA SAMPLES WITHOUT DERIVATIZATION

A direct high-performance liquid chromatographic assay for the determi nation of labetalol diastereoisomers in plasma without derivatization was developed. Baseline resolution of diastereoisomers was accomplishe d on a C18, bonded reversed-phase polymeric column with a basic (pH 11 .5) mobile phase and isocratic elution. Sample treatment was optimized in order to achieve a complete extraction of labetalol diastereoisome rs and to avoid racemization during extraction. Fluorimetric detection improved the selectivity and afforded a detection limit of 3 ng/ml fo r each diastereoisomer. This method is suitable for routine quantifica tion of labetalol diastereoisomers and has been applied to a pharmacok inetic study in small laboratory animals.