Influence of pH and pKa values on electrophoretic behaviour of quinolones in aqueous and hydro-organic media

Through correct pH measurements, pKa and activity coefficient values, a model describing their effect on electrophoretic behaviour of substances is established. The suggested model uses the pH values in the acetonitrile–water mixtures used and takes into account the effect of activity coefficients. The model permits the calculation of acidity constants of analytes in hydro-organic media and also the prediction of the effect of pH on the electrophoretic mobility. The model is tested by determining the dissociation constants of a series of nine quinolones in acetonitrile–water mixtures of 0, 5.5, 10 and 30% (w/w) acetonitrile.