PURITY CONTROL OF OXYTETRACYCLINE BY CAPILLARY ELECTROPHORESIS

The applicability of capillary electrophoresis for the purity control of oxytetracycline (OTC) was investigated. OTC is a broad-spectrum ant ibiotic belonging to the group of the tetracyclines. Several related s ubstances can be present due to fermentation or degradation, such as 4 -epioxytetracycline, alpha-apooxytetracycline, beta-apooxytetracycline , anhydrooxytetracycline, 2-acetyl-2-decarboxamidooxytetracycline, tet racycline and 4-epitetracycline. Using fused-silica capillaries, the i nfluence of buffer type, buffer pH and buffer concentration were inves tigated. In all cases 1 mM EDTA was added to prevent metal-ion complex ation. The influence of the buffer counter-ion type was examined. Cons equently, some instrumental parameters were changed such as capillary length and diameter as well as capillary temperature and applied volta ge. The following method is finally proposed: fused-silica capillary, 1 (effective length)=38 cm, L (total length)=44 cm, 50 mu m LD.; buffe r, sodium carbonate 20 mM-EDTA 1 mM, pH 11.25; voltage, 10 kV; tempera ture, 10 degrees C. Linearity, limit of detection and limit of quantit ation were determined as well as the relative standard deviations for all the analytes involved. This method is less selective then existing liquid chromatographic methods but it may be used as a complementary tool in purity control and stability studies.