Improved Colorimetric Determination of Reserpine in Tablets Using 4-Caboxyl-2,6-dintrobenzene diazonium ion (CDNBD)

Purpose: To develop a simple, rapid and improved colorimetric method for the assay of reserpine in tablets Method: The method is based on the aromatic ring coupling of reserpine with 4-carboxyl-2,6dinitrobenzene diazonium ion with the consequent formation of an azo adduct. Optimization of reaction conditions and validation were carried out and the method applied to assay of reserpine in tablets. Result: Reserpine coupled readily with CDNBD and optimization of experimental conditions showed the reaction to be completed in 10 min at room temperature. A 1:1 drug to reagent stoichiometric ratio was obtained for the azo adduct formed. The adduct exhibited a bathochromic shift with respect to the drug and pronounced hyperchromic shift with respect to the reagent. Sample analyses were done using a colorimeter at 470 nm. The assays were linear and reproducible over the concentration range of 2.25 24 μg/mL. The new method was successfully applied in the assay of reserpine in tablets with a performance similar to the official (USP) spectrophotometric method (p > 0.05). This method represents a profound improvement on the previously reported colorimetric method for reserpine. Conclusion: The method developed is rapid and could find application in in-process quality control of reserpine.