Quantitative determination of the beta-blocker labetalol in pharmaceuticals and human urine by high-performance liquid chromatography with amperometric detection.

A rapid and simple high-performance liquid chromatographic (HPLC) method with amperometric detection has been developed for the quantitation of labetalol in urine. The chromatography was performed at 30 degrees C using a reversed-phase column with a base deactivated silica stationary support and an alkylamide bonded phase (Supelcosil ABZ+Plus). A 5 mM acetate buffer (pH 4.5)-acetonitrile (70:30, v/v) mixture was employed as the mobile phase, pumped at a flow-rate of 1 ml/min. Sample preparation was carried out using a simple solid-phase extraction (SPE) procedure, and recoveries higher than 85% were achieved. The method was found to be accurate, precise (R.S.D lower than 8%), and sensitive enough (experimental quantitation limit of 20 ng/ml, detection limit 10 ng/ml) to be applied to doping analysis and pharmacokinetic studies in human urine. The method was applied to the determination of labetalol in pharmaceutical formulations and urine samples obtained from a healthy volunteer after the ingestion of a therapeutic dose of the drug, and the results obtained were in agreement with the pharmacokinetic data.