New Spectrophotometric Methods for Sildenafil Citrate

Abstract

Two simple, rapid and sensitive spectrophotometric methods for the determination of sildenafil in bulk samples and in formulations is described. The method A is based on the reaction between sildenafil citrate and diazotized dapsone in sodium hydroxide media and method B is based on the reaction between sildenafil citrate and diazotized p-sulphanilic acid in sodium hydroxide media. The graphs of absorbance vs. concentration show that Beer's law is obeyed over the concentration range 30-80 µg/mL for method A at 475 nm with molar absorptivity 0.7674 × 10³ mol^-1 cm^-1 and for method B it was 20-100 µg/mL at 420 nm with molar absorptivity 9.461 × 10³ mol^-1 cm^-1. These methods were applied for the analysis of pure drugs and commercial formulations containing sildenafil citrate. The commonly encountered excipients and additives do not interfere with the determination. These methods offer the advantages of simplicity, rapidity and sensitivity without the need for extraction or heating.