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 → π) mechanism, to yield a 1:1 complex with analytically useful maximum absorption at 495 nm, is described. The estimated molar absorptivity, ∊, and the stability constant, K, are 0.44 × 104 L mol−1 cm−1 and 1.06 × 106 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 μg/ml of norfloxacin. The concentration range of best accuracy deduced from Ringbom plot was 15–40 μ/ml norfloxacin. When the proposed method was applied to the analysis of commercial tablets (Noroxin®), 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....