Comparison between capillary electrophoresis, liquid chromatography, potentiometric and spectrophotometric techniques for evaluation of pKa values of zwitterionic drugs in acetonitrile–water mixtures

Capillary electrophoresis, liquid chromatography, potentiometry and UV–visible spectrophotometry are frequently used for determination of pKa values of substances. In this work, we have compared the application of the different techniques to the determination of pKa values of a series of zwitterionic quinolones in acetonitrile–water mixtures, emphasizing the advantages of capillary electrophoresis for the determination of equilibrium constants of widely used drugs in aqueous and aqueous organic media.