Colorimetric determination of tetracycline hydrochloride in pharmaceutical preparations

A simple, sensitive, and rapid colorimetric method is presented for the estimation of tetracycline hydrochloride as the pure drug and in formulations. The proposed method is based on the reaction of tetracycline HCl with cupric chloride in an alkaline medium to give a yellowish green solution whose absorbance is measured at 400 nm against a reagent blank. The color obeys Beer's law in the concentration range of 0-20 micrograms/mL. Molar absorptivity and Sandell's sensitivity of the yellowish-green copper complexes of tetracycline HCl are 1.99 X 10(4) L X mol-1 X cm-1 and 0.0241 ppm, respectively.