Tropical Journal of Pharmaceutical Research
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Novel colorimetric assay of mefenamic acid using 4-amino-3,5-dinitrobenzoic acid (ADBA)

SO Idowu, SC Tambo, AO Adegoke and AA Olaniyi

Department of Pharmaceutical Chemistry, Faculty of Pharmacy, University of Ibadan, Ibadan.

Trop J Pharm Res, June 2002; 1(1): 15-22

Abstract Full-Text

Purpose: To develop a novel colorimetric assay method for mefenamic acid capsules.

Method: The new method (aromatic ring derivatization technique) is based on a diazo coupling reaction using diazotized 4-amino-3,5-dinitrobenzoic acid (ADBA) as a chromogenic derivatizing reagent.

Result: Optimization studies showed that the coupling reaction is very fast and completed in less than 1 minute. A 1:1 drug to reagent stoichiometric ratio was obtained for the azo dye formed. The azo adduct formed exhibits bathochromic shift with absorption maximum (lmax) at 490 nm, which was selected as the analytical wavelength. Lower limit of quantitation of mefenamic acid was 1 mg/ml. The assays were linear over the concentration range of 1 - 6 mg/ml and reproducible. This new method has been successfully applied in the assay of mefenamic acid capsules with accuracy similar to the official (B.P) titrimetric method of assay (p>0.05) and has the advantages of speed, high sensitivity, lower limit of detection and can be automated.

Conclusion: The method developed could find application in in-process quality control of mefenamic acid capsules.

Keywords: Mefenamic acid assay, 4-amino-3,5-dinitrobenzoic acid, colorimetry, diazotization.

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Last updated: August 2002