Electrochemical determination of partition coefficients of drugs

An electrochemical method for the determination of partition coefficients of drugs that can exist as ions in aqueous solutions is presented. The method involves cyclic voltammetry at the polarizable interface between two immiscible electrolyte solutions. Because n-octanol is an unsuitable solvent for electrochemical purposes, 1,2-dichloroethane, which has electronic properties similar to those of n-octanol, was used in the measurements. The values obtained could be correlated with the values for n-octanol-water partition taken from the literature by an approach based on the linear solvation relationship: log P1 = a log P2 + b; in this relationship, a and b are constants and P1 and P2 correspond to the two different organic and aqueous phase partition equilibria. Furthermore, aqueous diffusion coefficients of drugs were determined from voltammograms.