Quantitative analysis of chlortetracycline and related substances by high-performance liquid chromatography.

Isocratic high-performance liquid chromatography on Zorbax C8 7 microns allows quantitative determination of chlortetracycline, 4-epichlortetracycline, tetracycline, demethylchlortetracycline and isochlortetracycline using a mobile phase containing dimethylsulphoxide, 1 M perchloric acid and water (35:5:60). The minor impurities anhydrochlortetracycline and 4-epianhydrochlortetracycline, which are more strongly retained can be determined using a second isocratic system with a mobile phase containing more organic modifier. The method has been used for the comparison of official standards and for the analysis of a number of commercial samples.