High-performance liquid chromatographic method for the determination of the major quinine metabolite, 3-hydroxyquinine, in plasma and urine

The determination of 3-hydroxyquinine in urine and plasma samples is described. Extraction was performed using a mixture of toluene–butanol (75:25, v/v), followed by back-extraction into the mobile phase, which consisted of 0.1 M phosphate buffer, acetonitrile, tetrahydrofuran and triethylamine. A reversed-phase liquid chromatography system with fluorescence detection and a CT-sil C₁₈ column were used. The within-assay coefficient of variation of the method was 2% at the higher concentration values in plasma, 2.95 μM, 4% at 227 nM and 9% at the lower limit of quantitation, 4.5 nM. In urine, the coefficient of variation was 11% at the lower concentration, 227 nM and was 3% at 56.8 μM. The between-assay coefficient of variation was 4% at the low concentration (5.1 nM) in plasma, 2% at 276.8 nM and 3% at 1.97 μM. In urine, the between assay coefficient of variation was 4% at 204.6 nM, 3% at 5.12 μM and 2% at 56.8 μM.