Capillary electrophoresis in mixed aqueous-organic media:: Effect of tetrahydrofuran on mobilities, dissociation constants and separation of a series of quinolones

The influence of the composition of aqueous-twtrahydrofuran mixtures on the electrophoretic behaviour of nine quinolones was studied in order to predict the optimum conditions for their separation. The effect of pH, pK(a) and activity coefficients on electrophoretic behaviour was established. Standard pH values for buffer solutions of the NIST scale as previously determined in THF-water were used in accordance with IUPAC rules. pH was therefore measured for these media as for water. The pK(a) valves of quinolones were determined from the electrophoretic mobilities-pH data pairs in different THF-water mixtures. The electrophoretic resolution between pairs of substances was then predicted in order to obtain the optimal experimental conditions for separation methodologies.