A Sensitive and Simple High Performance Liquid Chromatographic Method for Quantification of Tadalafil in Human Serum

A simple, rapid, and sensitive high-performance liquid chromatographic method was developed and validated for determination of tadalafil, a selective and reversible phosphodiesterase inhibitor, in human serum. Methylparaben was used as the internal standard. Optimum conditions for tadalafil assay were investigated. The analyte and internal standard were extracted by a single-step liquid–liquid extraction with dichloromethane in alkaline serum. The chromatographic separation was performed on reverse phase LiChrospher 100, C18 column (Agilent Technologies, Palo Alto, CA) with a mobile phase consisting of 35% acetonitrile-65% water containing 0.1 mM glacial acetic acid (pH 2.5-2.7). Ultraviolet detection was performed at 280 nm. Detection limit was 1.5 ng/mL, and limit of quantification was less than 10 ng/mL for tadalafil. The cali-