Determination of Doxepin in human plasma using cloud‐point extraction with high‐performance liquid chromatography and ultraviolet detection

: A new straightforward method based on cloud-point extraction has been developed, optimized, and validated for the determination of doxepin in human plasma by high-performance liquid chromatography separation and UV detection. The nonionic surfactant Triton X-114 was chosen as the extraction solvent. Chromatography separation was performed on a μBondapakR C18 column (4.6 mm id × 300 mm, 3 μm particle size), which was used for isocratic elution at a detection wavelength of 289 nm. Under the optimum conditions, the linear range of doxepin in human plasma was 0.1-0.9 μg/mL. Also, the detection limit, preconcentration factor, and enrichment factor were 0.08 μg/mL, 50, and 49.0, respectively.