Spectrophotometric Determination of Mefenamic Acid in Pharmaceutical Preparations Via Arsenazo III – Cerium (III) Reaction*

A sensitive indirect spectrophotometric method is proposed for determining mefenamic acid in pure form and in its pharmaceutical preparations. The method is based on oxidation-reduction reaction between mefenamic acid and cerium (IV) ion, and subsequent Ce(III) reaction with arsenazo (III) reagent in acidic medium to produce a greenish-blue complex which is stable, water soluble and has a maximum absorption at 654 nm with a molar absorptivity of 1.731105 l.mol-1.cm-1. Beers law is obeyed in the concentration range from 1 to 10 g mefenamic acid in a final volume of 25 ml. The proposed method has been applied successfully to determine mefenamic acid in pharmaceutical preparations.