A simple and senstive kinetic spectrophotometric method was developed for the determination of tetracycline in capsule dosage forms. The method is based on the reaction of tetracycline with potassium permanganate in alkaline medium to form a green color of potassium mangante at room temperature. The reaction is followed spectrophotometrically by measuring the rate of change of absorbance at 610 nm. The absorbance-concentration plot was rectilinear over the range of 1.0-30.0 μg/ml with limit of detection (LOD) of 0.96 μg/ml and limit of quantification (LOQ) 3.22 μg/ml. Different experimental parameters affecting the development and stability of the colour were carefully studied and optimized. The determination of tetracycline by the fixed-concentration and rate-constant methods is also feasible with the calibration equations obtained, but the fixed time method has been found to be more advantageous. The proposed method was further applied to the determination of the drug in formulations. The results obtained were in good agreement with those obtained using the official method. A proposal of the reaction pathway was postulated.
