Development and validation of a colorimetric method for determination of tadalafil using ion-pair complexation with bromophenol blue

Tadalafil belongs to the class of phosphodiesterase (PDE5) inhibitors used for the management of erectile dysfunction and other conditions. The study reports a colorimetric method for the determination of tadalafil. The method is based on the reaction of the drug with bromophenol blue in acetate buffer (pH 2.8) to form a yellow coloured complex showing maximum absorbance at 415 nm. A linear calibration curve was obtained between 2 and 22 μg/mL of tadalafil with correlation coefficient (r2) of 0.972 and molar absorptivity of 15,267 Lmol-1cm-1. The method similarly demonstrated good precision with intra-day precision ranging from 3.68-5.89 %RSD and inter-day precision of 0.66 – 4.45 % RSD. The developed method was successfully applied to the analysis of tadalafil in tablet formulation and could serve as a useful tool in the quality assessment of this medication.