IONIC PARTITION DIAGRAMS - A POTENTIAL PH REPRESENTATION

A general method to predict and interpret the transfer mechanisms of i onizable compounds at the interface between two immiscible electrolyte solutions (ITIES) is presented. The approach is based on the construc tion of the ionic partition diagram of the solute. It consists in defi ning equiconcentration boundaries as a function of the Galvani potenti al difference and aqueous pH by taking into account the thermodynamic equilibria governing the distribution of the various acid/base forms o f the molecules involved. The method defines the domains of predominan ce of each species either in the aqueous or in the organic phase. The application of ionic partition diagrams to quinidine offers a global a nd direct visualization of all the species and demonstrates the validi ty and efficiency of the method in helping to understand the transfer and partition mechanisms of ionizable drugs.