SEPARATION AND CHARACTERIZATION OF TETRACYCLINE ANTIBIOTICS BY CAPILLARY ELECTROPHORESIS

The electrophoretic behavior of the antibiotics tetracycline, chlortet racycline, demeclocycline, oxytetracycline, doxycycline, methacycline and minocycline has been characterized by capillary electrophoresis in phosphate buffer solutions in the pH range 4-11. A complete set of ac id-base equilibrium constants and electrophoretic mobilities was deter mined and, subsequently, was used in a computer-assisted optimization program to assess the separation of the tetracyclines. Under the predi cted optimum conditions (pH 7.5, 18.2 mM ionic strength, 4.3 mM buffer concentration, and constant current of 20 mu A), the separation was p erformed satisfactorily and all tetracyclines were readily identified. Moreover, the common impurities in tetracycline resulting from dehydr ation and epimerization reactions were discriminated under the same co nditions. The determination of tetracycline, doxycycline and minocycli ne was performed in commercially available pharmaceutical formulations . During the dissolution of the contents of hard-filled capsules, a mi nimum recovery of 95% of the active ingredient was obtained. A calibra tion curve of peak height versus concentration gave a slope of 6.15.10 (-4) cm M(-1), intercept of -1.18.10(-5) cm, and coefficient of determ ination equal to 0.9989. The analysis using UV-absorbance detection at 260 nm provided a detection limit of 1.10(-5) M at a signal-to-noise ratio of approximately 3, with a linear range of two orders of magnitu de.