Spectrophotometric Determination of Mesalazine by Diazotisation-Coupling Method with Resorcinol

A simple spectrophotoemtric method for the determination of mesalazine [5-aminosalicylic acid; (5-ASA)] in aqueous solution is achieved. The method is based on the reaction of mesalazine, with excess nitrite, in an acidic medium, to produce the corresponding diazonium salt. After the removal of residual nitrite with sulphamic acid, the diazonium salt is coupled with resorcinol reagent in basic medium to produce, an intense orange coloured water-soluble and stable azo-dye which exhibits maximum absorption at 471nm. Beers law is obeyed in the concentration range of 10-300g of mesalazine in a final volume of 25 ml i.e., 0.4-12 ppm with a molar absorptivity of 2.9480104 l.mol-1.cm-1 and Sandell sensitivity index of 0.0051g.cm-2, a relative error of -0.96 to -0.23% and relative standard deviation of 1.05 to 0.37% depending on the concentration level. The proposed method has been applied successfully to determine mesalazine in pharmaceutical preparation (capsules).