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Utility of Ion-associate Formation Reactions for the Spectrophotometric Determination of Sildenafil Citrate in Pure form and in Virecta Tablets

Eman Y.Z. Frag, Gehad G. Mohamed and Hana M.S. Alelaiwi

A simple, rapid and sensitive extractive spectrophotometric method has been developed for the assay of sildenafil citrate (SILC) in pure and pharmaceutical formulations (Virecta tablets). This method is based on the formation of chloroform soluble ion-pair of SILC with bromothymol blue (BTB) and methylene chloride soluble ion- pair of SILC with bromophenol blue (BPB) and eriochrome blue black R (EBBR) in borax buffer of pH 3 and volume 1mL for BTB while acetate buffer of pH 3 and volume 1mL for BPB and universal buffer of pH 2 and volume 1.5 mL for EBBR with absorption maximum at 415, 420 nm and 510 nm for BTB, BPB and EBBR reagents, respectively. Reaction conditions were optimized to obtain the maximum colour intensity. The absorbance was found to increase linearly with the increase in SILC concentration, which was corroborated by the calculated correlation coefficient values (0.9909, 0.9901 and 0.9917 for BTB, BPB and EBBR reagents, respectively). The systems obeyed Beer’s law over the concentration range of 1-40, 1-50 and 3-70 μg mL -1 for BTB, BPB and EBBR, respectively. Various analytical parameters have been evaluated and the results have been validated by statistical data. No interference was observed from common excipients present in pharmaceutical formulations.