Spectrophotometric determination of tetracycline and oxytetracycline in pharmaceutical preparations

A simple, rapid and sensitive spectrophotometric procedure for the assay of tetracycline hydrochloride and oxytetracycline hydrochloride has been developed. 2,2-Diphenyl-l-picrylhydrazyl (DPH), an intensely violet-coloured stable free radical, is changed in colour on reaction with the antibiotics investigated. The decrease in the intensity of the violet colour is used to measure the concentration of the drug. All measurements are made at 520 nm on methanolic solutions of the drug and reagent, buffered at pH 6. Beer's law is obeyed in the concentration ranges 2.5-15 and 2.5-20 mug/ml for tetracycline and oxytetracycline respectively. The proposed method has been successfully applied to analysis of the bulk drugs and their pharmaceutical formulations.