Affiliations: Department of Chemistry, Faculty of Science, Zagazig University, Zagazig, Egypt
Note: [] Corresponding author: Akram M. El-Didamony, Department of Chemistry, Faculty of Science, Zagazig University, Zagazig 44511, Egypt. E-mail: ak_eldidamony@yahoo.com
Abstract: Three simple and sensitive spectrophotometric methods were developed for the estimation of captopril (CAPT) in pure form or in tablet formulations. The three methods are based on the reactivity of the thiol group. The first two methods (A and B) are based on the oxidation of CAPT by bromate/bromide mixture of known concentration in acid medium. In method A, the determination of the residual bromine is based on its ability to bleach the methylene blue dye and measuring the absorbance at 664 nm. Method B involves treating the unreacted bromine with a measured excess of iron(II) and the remaining iron(II) is complexed with 2,2′-dipyridyl and the increase in absorbance is measured at 523 nm. Method C involves the addition of a known excess amount of potassium dichromate in acidic medium, followed by the estimation of unreacted amount of dichromate by reacting with excess of iron(II). The resulting iron(III) is complexed with thiocyanate and the absorbance is measured at 478 nm. In all the methods, the amount of oxidant reacted corresponds to the drug content. The different experimental parameters affecting the development and stability of the color product are carefully studied and optimized. After validation, the proposed methods were successfully applied to assay of CAPT in its commercial tablets. No interference was observed from common additives found in pharmaceutical preparations. The results were statistically compared with those of a reference method by applying Student's t- and F-test.
