4-aminosalicylic acid as a coupling reagent for spectrophotometric determination of mesalazine in an aqueous medium

A sensitive, rapid, and inexpensive spectrophotometric method for the determination of mesalazine in an alkaline medium by an oxidative coupling reaction was developed. At a wavelength of about 600 nm,  mesalazine could be estimated in the range (0.1–14) µg/ml with high sensitivity, since the molar absorption was 7.6×103 L.mol-1.cm-1 and the Sandell index was 0.0201 µg/cm2, with a recovery rate of 101.6% and a lower relative standard deviation from  1.2%, the synthesis ratio of the dye product was tested and found to be 1:1 (mesalazine:4-aminosalicylic acid) and the dye stability constant value was 8.51×105. The method was successfully applied to the determination of mesalazine in its pharmaceutical preparations, which were in the form of compressed tablets, and the results agreed with the authentic contents of the pharmaceutical preparation and the British Pharmacopoeia-approved method.