Determination of cocaine and its metabolites in serum microsamples by high-performance liquid chromatography and its application to pharmacokinetics in rats

A single-solvent extraction step high-performance liquid chromatographic method is described for quantitating cocaine and its three metabolites in rat serum microsamples (50 μl). The separation used a 2.1-mm I.D. reversed-phase Brownlee C₁₈ column with an isocratic mobile phase consisting of methanol–acetonitrile–25.8 mM sodium acetate buffer, pH 2.2, containing 1.29·10⁻⁴M tetrabutylammonium phosphate (12.5:10:77.5, v/v/v). The detection limit was 2.5 ng/ml for all the compounds using an ultraviolet detector operated at 235 nm. The method was used to study the pharmacokinetics of cocaine after an intravenous (i.v.) bolus dose (4 mg/kg).