Optimisation of mobile phase pH in liquid chromatography. Application to fluorimetric detection of series of quinolones

The dissociation constants of several quinolones in a 7 % acetonitrile-wate r mixture are determined. A model describing the effect of pH on the retent ion of quinolones by an octadecylsilica stationary phase with a 7 % acetoni trile-water mobile phase is proposed. The model uses pH values in the mobil e phase instead of pH values in water and takes into account the effect of activity coefficients. Fluorescence of quinolones in the mobile phase is st udied, and a chromatographic separation with fluorimetric detection is esta blished. Detection limits for the proposed method range from 3 to 12 mu g.L -1.