SPECTROPHOTOMETRIC DETERMINATION OF MINOXIDIL IN PURE FORM AND ITS PHARMACEUTICAL PREPARATIONS

Four simple, accurate, sensitive and economical procedures (A-D) for the estimation of minoxdil, both in pure form and in pharmaceutical formulations have been developed The first method (A) is based on the Oxidatton of the studied drug by a known excess of potassium permanganate in sulfuric acid medium directly .followed by measuring the decrease in absorption of KMnO₄ , (A method ) at 525.6 nm. The second method (B) is based on the same principle with subsequent determination of unreacted potassium permanganate using methylene blue dye in the same acid medium at a suitable 66- am. The third method is based on measuring manganate produced from the reaction of minoxidil with potassium permanganate in sodium hydroxide medium at ʎ_max 610 nm. While the fourth method is based on oxidation of the drug by Fe³⁺ in the presence of bipyridyl (bipy) in acetate buffer of pH 4.22 resulting in the formation of tris-complex which demonstrated at ʎ_max 530 nm. Regression analysis of Beer-lambert plots showed good correlations in the concentration ranges 8 0-40 . 2.0-20 and 2.0- 10 g ml respectively. Molar absorptivity and Sandell's sensitivity were calculated for each method the optimum reaction conditions and other analytical parameters were evaluated. The proposed methods were applied to the determination of this drug in laboratory prepared tablets which contains the same contents of Loniten tablets .produced by ( Pharmacia and Upjohn). The influence of the substances commonly employed as excipients with this drug were studied. The suggested methods were compared with reference one results have demonstrated that the methods are equally accurate and reproducible as the reference method