Validated Methods for Determination of Sildenafil Citrate in The Presence of its Potential Impurities

Two simple, accurate, sensitive and reproducible methods have been developed and subsequent validated for the determination of Sildenafil citrate (SC) in presence of its impurities “1-methyl-4-nitro-3-n-propyl-5pyrozole Carboxamide (MNC), 4-amino-1-methyl-3-n-propyl-5-pyrazole Carboxamide (AMP), 4-(2-ethoxy benzoyl amino)-1-methyl-3-n-propyl-5-pyrazole Carboxamide (EMC) and 5-(2-ethoxyphenyl)-1-methyl-3-n-propyl pyrazole [4,3-D] pyramidine-7-1(EMP)” as stability-indicating studies. In the spectrophotometric method, zerocrossing technique was adopted for determination of the investigated drug in presence of impurities, by the use of derivative and derivative ratio techniques, respectively. While, the second method was isocratic reversedphase (RP) stability-indicating high-performance liquid chromatographic method, which was adopted for determination of Sildenafil citrate in presence of its impurities. The chromatographic separation was achieved isocratically by using a mobile phase of water and acetonitrile in a ratio of 40:60 V/V containing 50 mM triethylamine. The analysis was carried out using waters C18 (4.6 x 250 mm, 10 μm) at flow rate of 1.0 ml.min and the UV detection at 245 nm. All the proposed methods were validated according to the International Conference on Harmonization (ICH) guidelines reference and successfully applied for determination of Sildenafil citrate in pure form, in laboratory prepared mixtures and in pharmaceutical preparations. The obtained results were statistically compared to the reported method of analysis for Sildenafil citrate and no significant differences were found.