The transfer mechanisms and analytical properties of the variable-valency drug cinchonidine across the liquid/liquid interface

Abstract

The electrochemical transfer of cinchonidine across the liquid/liquid (L/L) interface was investigated by linear current-scanning polarography at the ascending water electrode and chronopotentiometry at the stationary water electrode. The relation between half-wave potential and the pH value of the aqueous phase was established and is in good agreement with the experimental results. Defending on the pH value in the aqueous phase, both singly- and doubly-charged cinchonidine cations can transfer across the L/L interface. This process is controlled simultaneously by diffusion and the rate of re-establishment of the disturbed protonation equilibrium. The effects of the supporting electrolyte, buffer and organic solvent on the polarographic wave were examined, and the transfer characteristics of cinchonidine in the aqueous and organic phases were compared. Direct determinations of cinchonidine in the aqueous phase and organic phase were carried out by linear current-scanning polarography with high selectivity. The linear range for determination is 5 × 10 −5−1 × 10 −3 mol dm −3.