Separation and quantitative determination of impurities in tetracycline.

Anhydrotetracycline, epianhydrotetracycline, epitetracycline, and chlortetracycline are generally found as impurities in tetracycline. A new thin-layer partition chromatographic method is described in which the impurities are separated on a kieselguhr layer impregnated with ethylene glycol-water-acetone-ethyl acetate (2:2:15:15). Compared to previous methods, this determiniation is easier to perform and more versatile and it prevents rapid epimerization. The quantitative determination of the tetracyclines utilizes spectrophotometry or direct TLC fluorometry.