Abstract
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-2,6-dinitrobenzene 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. Keywords: Reserpine, colorimetry, 4-Caboxyl-2,6-dintrobenzene diazonium ion (CDNBD), diazo coupling > Tropical Journal of Pharmaceutical Research Vol. 6 (2) 2007: pp. 695-703
Highlights
Reserpine is an alkaloid obtained from the roots of certain species of Rauwolfia (Apocyanaceae) mainly R. serpentina and R. vomitoria or by synthesis
In continuation of our work on the development of relatively simple colorimetric methods for the assessment of organic compounds of pharmaceutical importance[13,14,15,16,17], we report a new colorimetric method for the determination of reserpine in bulk and tablet dosage form using the newly developed 4carboxyl-2, 6-dinitrobenzene diazonium ion (CDNBD) 18-20
Reserpine was found to couple instantly with CDNBD and the colour remained stable at room temperature for days
Summary
Reserpine is an alkaloid obtained from the roots of certain species of Rauwolfia (Apocyanaceae) mainly R. serpentina and R. vomitoria or by synthesis. Reserpine has been used in the management of hypertension and in chronic psychoses such as schizophrenia. It has been tried in the management of Raynaud’s syndrome Chemically, reserpine is (3β, 16β, 17α, 18β, 20α)-11, 17-dimethoxy-18 [(3, 4, 5trimethoxybenzoyl)-oxyl] yohimban-16-carboxylic acid methyl ester or 3,4,5-trimethoxybenzoyl methyl reserpate[3]. The USP 24/NF 195, uses a UV method for all Rauwolfia preparations after exhaustive and extensive solvent extraction. Other multi-ingredient preparations containing reserpine are assayed by HPLC methods in the USP 24/ NF 19. The determination of reserpine and other indole alkaloids from Rauwolfia serpentina and R. vomitoria by HPLC and HPTLC has been reported. Other chromatographic procedures are described[8]
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