Prediction of electrophoretic behaviour of a series of quinolones in aqueous methanol

Quinolones are a family of antibacterial agents used in human and veterinary clinics. The examination of protonation equilibria is essential because their antibacterial activity is pH-dependent. In this work, dissociation constants of quinolones in MeOH–water mixtures were obtained using capillary electrophoresis. The method is based on a model that relates electrophoretic mobility of the solute with pH. The effect of pH, pKa and activity coefficient on electrophoretic behaviour was considered. Standard pH values for buffer solutions were previously determined in MeOH–water mixtures, and the pH can thus be measured in these media as in water. This model is also used to obtain the optimum conditions for the separation of a series of substances because it allows one to predict the resolution between adjacent peaks from a few experimental data.