Indirect Spectrophotometric Method for the Determination of Mefenamic Acid in Pharmaceutical Formulations*

A simple, sensitive and accurate spectrophotometric method for the determination of mefenamic acid in pure form and in some pharmaceutical formulations was developed. The method is based on the oxidation of mefenamic acid by iron(III), and subsequent complexation of iron(II) with o-phenanthroline, forming a red-colored complex (ferroin) having the maximum absorbance at 510 nm. Beer's law is obeyed in the concentration range of 0.4-2.0 gml, the molar absorptivity and Sandell's sensitivity are 2.9104 L.mol-1.cm-1 and 8.3 ng.cm-2, respectively and the relative standard deviation (RSD) is less than 2.0 (n=10). The limits of detection and quantitation are 0.065 and 0.195 g.ml-1,respectively. The method is applied successfully to determination of mefenamic acid in some pharmaceutical formulations (capsules and tablets). The common excipients do not interfere with the proposed method. A statistical comparison of these results with those of official method using (t and F) values at 95% confidence level shows good agreement and indicates no significant difference in the precision and the present method has good validity.