Direct Spectrophotometric Determination of Sildenafil Citrate in Pharmaceutical Preparations via Complex formation with Two Sulphonphthalein Acid Dyes

Objective: Simple, sensitive and free- extraction spectrophotometric methods have been developed for the determination of Sildenafil citrate (SIL) both in pure and in pharmaceutical forms. Methods: Two spectrophotometric methods are based on the formation of yellow colored ion-pair complexes between the studied drug and two sulphonphthalein acid dyes, bromocresol green (BCG)(method A) and bromothymol blue (BTB) (method B) with absorption maxima at 414 and 409 nm, respectively.

Results: The effects of analytical parameters on the reported systems were investigated. The complexation reactions were extremely rapid at room temperature and the absorption values remain unchanged up to 24h. Various analytical parameters have been evaluated and the results have been validated by statistical. Beer's law was obeyed in the concentration ranges of (1.33 - 50) μg/ml for method A and (0.8 -27) μg/ml for method B, the limits of detection were 0.093 and 0.059 μg/ml and the molar absorptivity coefficients were 2.28×104 and 3.05 ×10⁴ L .moL^-1.cm^-1 for method A and B respectively.

Conclusion: The proposed methods were successfully applied to the analysis of commercial tablets containing the drugs. Two methods were free-extractive, rapid, and have high sensitivity comparing with other previous direct spectrophotometric methods. Interferences of the other ingredients and excipients were not observed.