CAPILLARY ZONE ELECTROPHORESIS OF MINOCYCLINE

A method is described for analysis of the tetracyline antibiotic minoc ycline using capillary zone electrophoresis. Potential impurities are 4-epiminocycline, 6-deoxy-6-demethyltetracycline, 7-didemethylminocycl ine, 7-monodemethylminocycline and 9-minocycline. Method development w as undertaken with a mixture consisting of minocycline and its related substances mentioned above. Using a fused silica capillary, the type of buffer and its pH and concentration were investigated. In all cases 1 mM EDTA was added to prevent metal ion complexation. Instrumental p arameters such as capillary temperature and applied voltage were optim ised. The effects of the sample solvent and of organic modifiers in th e buffer were also investigated. The following method is proposed: cap illary: fused silica, l = 38 cm, L = 44 cm, 50 mu m i.d.; buffer: 25 m M sodium tetraborate, 1 mM EDTA at pH 11.75; voltage, 13 kV; temperatu re, 15 degrees C; UV detection performed at 254 nm. Relative standard deviations, linearity, LOD and LOQ are reported and compared with thos e of liquid chromatography.