Colorimetric determination of tetracycline derivatives in pharmaceutical preparations.

A quick colorimetric method is reported for the determination of tetracycline derivatives such as oxytetracycline hydrochloride (OTCH), chlortetracycline hydrochloride (CTCH), methacycline hydrochloride (MCH), and doxycycline hydrochloride (DCH). The method involves complexation of the above derivatives with cupric chloride in alkaline medium. The yellowish green copper complexes of OTCH, CTCH, MCH, and DCH show maximum absorbance at 395, 410, 400, and 400 nm, respectively. The color intensity obeys Beer's law in the concentration range of 0-20 micrograms/mL.