Polyelectrolyte–surfactant complexes: an aqueous titration method to model ion-pairing within polymeric membranes of polyion-sensitive electrodes

Abstract

A model for estimating the degree of cooperative ion-pairing that occurs between polyions and lipophilic ion-exchangers doped into the organic polymer membranes of polyion-sensitive electrodes has been developed. The binding of several polyanionic (e.g., heparins, carrageenans, polyphosphates, and polyglutamates) and polycationic species (e.g., protamine, polyarginine, and polylysines) with water soluble surfactants, quaternary ammonium and alkyl- and alkylbenzene sulfonates, respectively, which are structurally analogous to the ion-exchangers, is monitored in aqueous solutions with surfactant-selective electrodes. Analysis of the binding data reveals that the polyion structure, including polyion molecular weight, lipophilicity, and charge density, has a significant impact on the observed binding affinities, as does the surfactant structure. It is also shown that the measured aqueous phase binding affinities have a strong linear correlation with the equilibrium EMF changes observed with the respective polyion-sensitive electrodes, confirming the validity of using an aqueous system to model the binding behavior of ion-exchangers with polyions within the organic polymer membranes of polyion-sensitive electrodes.