Determination of venlafaxine in human plasma by high-performance liquid chromatography using cloud-point extraction and spectrofluorimetric detection

A new straightforward method based on cloud-point extraction (CPE) has been developed, optimized and validated for the determination of venlafaxine in human plasma by reversed-phase high-performance liquid chromatography with fluorescence detection. The non-ionic surfactant Triton X-114 (polyethylene glycol tert-octylphenyl ether) was chosen as the extract solvent. Separation was obtained using a reversed-phase Diamonsil column (C18, 250 mm × 4.6 mm I.D., 5 μm) and a mobile phase composed of acetonitrile–phosphate buffer solution (pH 3.0)–triethylamine (33.5:66.5:0.4). Fluorescence detection was used (λex 276 nm, λem 598 nm). Maprotiline was used as the internal standard. Under the optimum conditions, the linear range of venlafaxine in human plasma was 10–800 ng mL−1 (r2 = 0.9995). The limit of detection (LOD) was less than 2 ng mL−1 (S/N = 3) and the limit of quantification (LOQ) was less than 10 ng mL−1 (S/N = 10). The method was successfully applied for the evaluation of pharmacokinetic profiles of venlafaxine capsules in nine healthy volunteers.