Abstract
This work presents two simple and direct spectrophotometric methods for determination of the carbonic anhydrase inhibitor brinzolamide (BNZ) through charge transfer complexation reactions. This work is considered the first investigation for colorimetric methods for estimation of BNZ. Method I is based on reaction of the drug with p-chloranilic acid (p-CA) in acetonitrile to give a red colored product with maximum absorbance at 521 nm. Method II is based upon the interaction of BNZ and picric acid (PA) in chloroform resulting in the formation of a yellow complex measured at 407 nm. Factors affecting the color development were studied and optimized. Stoichiometry of the reactions was determined. The proposed colorimetric procedures were validated with respect to linearity, ranges, precision, accuracy, robustness, detection and quantification limits. Regression analysis for the calibration curves of the formed color products with p-CA and PA showed good linear relationships over the concentration ranges of 40-360 and 8-48 mu g/mL respectively. The method was successfully applied to the assay of BNZ in its pharmaceutical preparation (ophthalmic suspension) with good accuracy and precision. Assay results were statistically compared to a reference pharmacopoeial HPLC method where no significant differences were observed between the proposed methods and reference method.