Transfer mechanism of quinine drug across the oil/water (O/W) interface.

The transfer phenomena of quinine drug at the aqueous 1,2-dichloroethane (DCE) interface have been studied by the current-scanning polarography. The relationships between the wave height and pH of aqueous phase, concentration of quinine as well as the rate of water drop are discussed. The effect of supporting electrolyte, buffer solution and the nature of organic solvent on the polarographic wave is studied. The transfer characteristics of quinine in aqueous phase and in organic phase are compared. The mono-protonated and diprotonated quinines can both transfer at the interface so as to produce two polarographic waves. The transfer process of quinine at the interface is simultaneously controlled by diffusion and reestablishment of the disturbed protonated equilibrium of quinine. A further investigation is made by chronopotentiometry. On the basis of the theoretical analysis, the formulae of the limiting current are derived and discussed. The theoretical results are in agreement with the experimental ones. The transfer mechanism of quinine is put forward.