Separation of ibuprofen, codeine phosphate, their degradation products and impurities by capillary electrophoresis. I. Method development and optimization with fractional factorial design.

A capillary electrophoresis method has been developed and optimized for the separation of ibuprofen, codeine phosphate and their main degradation products and impurities. In the course of developing the method, it was found that micellar electrokinetic capillary chromatography was necessary for the separation of the eleven peaks. A fractional factorial design was used for the optimization of the experiments. Six process parameters were varied at two levels: the concentration of sodium dodecyl sulfate (SDS), the pH, the concentration of acetonitrile, the concentration of boric acid, the field strength and the temperature. All these factors had a significant effect on the migration time and resolution. The optimum conditions were found to be a borate buffer of 40 mM H3BO3 at pH 10 with the addition of 40 mM SDS and 9% acetonitrile, a field strength of 515 V/cm and a temperature of 25 degrees C. This resulted in baseline separation of the eleven peaks within 12 min.