COLOURIMETRIC DETERMINATION OF NORFLOXACIN IN TABLETS BY REACTION WITH P-BENZOQUINONE

A simple, quick and sensitive spectrophotometric method based on the combination of norfloxacin and p-benzoquinone at room temperature, apparently by charge-transfer (n --> pi) mechanism, to yield a 1:1 complex with analytically useful maximum absorption at 495 nm, is described. The estimated molar absorptivity, epsilon, and the stability constant, K, are 0.44 x 10(4) L mol(-1) cm(-1) and 1.06 x 10(6) L mol(-1) respectively. The role of solvent, p-benzoquinone concentration, pH and presence of water have been investigated. Under the optimized conditions, Beer's Law was obeyed over the concentration range 7.5 - 40 mu g/ml of norfloxacin. The concentration range of best accuracy deduced from Ringborn plot was 15-40 mu g/ml norfloxacin. When the proposed method was applied to the analysis of commercial tablets (Noroxin(R)), labeled to contain 400 mg of drug per tablet, the mean percentage found was 100.57 +/- 1.58 (n = 9). The precision and accuracy of the method proposed have been compared statistically with the official (U.S.P.) high performance-liquid chromatographic procedure using the F-ratio and Student-t tests.