SENSITIVE MICROBORE HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHIC ASSAY FOR LABETALOL IN THE BIOLOGICAL-FLUIDS OF PREGNANT SHEEP

A rapid and sensitive microbore high-performance liquid chromatographic (HPLC) assay is reported for the quantitation of labetalol, an anti-hypertensive agent, in small volumes (250-mu-l) of biological fluids (viz., maternal plasma, fetal plasma, amniotic fluid and fetal tracheal fluid) obtained from the chronically instrumented pregnant sheep. Labetalol was extracted from the samples using ethyl acetate and then partitioned into dilute phosphoric acid. Chromatography was performed on a microbore HPLC system using a 2.1 mm I.D. C18 column and detection was accomplished by a low-dispersion fluorescence detector designed for trace analysis. The drug was well separated from endogenous substances in all biological fluids sampled. The calibration curves were linear for all fluids over the range of study with mean coefficients of variation consistently below 5%. Quantitation was possible down to almost-equal-to 30 pg of labetalol injected (almost-equal-to 1.6 ng/ml in plasma using 250-mu-l).