Donnan Partitioning Research Articles

A numerical ac-impedance model used for the analysis of a polyvinylferrocene coated electrode

A numerical model to calculate the impedance plane plot of a redox polymer coated electrode bathed in an electrolyte solution is presented and used for the analysis of the experimental measurements of a polyvinylferrocene system. The model takes into account Butler-Volmer type heterogeneous redox kinetics, electron flux by hopping, diffusion and migration of the electrolyte, the Poisson's equation, Donnan partition kinetics, an IR-drop and the double layer capacitance including a constant phase element. This numerical procedure offers a powerful tool for analysing impedance data of very complex systems.

Simulation of time-dependent processes at redox polymer electrodes

A numerical simulation of a polymer-coated electrode is presented. The model accounts for the mass transport by diffusion and migration, electron transfer through the membrane by a hopping mechanism, homogeneous chemical reaction in the membrane, heterogeneous reactions and double-layer capacitance at the interface between electrode and membrane, and the Donnan partition equilibrium at the interface between membrane and diffusion layer. The set of partial differential equations is transformed into ordinary differential equations using the method of lines with cubic Hermitian polynomials. The time integration is performed by a semi-implicit method. Calculated and measured data of cyclic voltammograms of a ruthenium polymer-coated electrode are compared and demonstrate the reliability of the model.

Donnan partition parametric pumping. Concentration and dilution effects in ion exchange parametric pumping

Ion exchange parametric pumping has been studied in order to separate metals in solution such as Ag+ and Cu2+. All results in the literature show that phenomena other than pure ion exchange occur: concentration or dilution of the two products is observed. In this paper, specific parametric pumping experiments are presented, performed on a cation exchange resin with only one cation in the system; that is, without ion exchange. The results show that the electrolyte can be concentrated and diluted; the direction of the concentration-dilution effect greatly depends on the cation considered. An interpretation based on the temperature dependence of Donnan electrolyte partition explains all the results. In addition, we can expect application of this work in ion exclusion parametric pumping.

Influence of colloidal charge on response of pH and reference electrodes: the suspension effect

The pH measured in a charged sediment is often very different from that of the supernatant solution. This effect has been studied to determine whether it is caused by an anomalous junction potential at the reference electrode, as commonly thought, or by Donnan partitioning of hydrogen ions. Electrical conductivities in sediments of a strong cation-exchange resin were much higher than predicted by the junction artifact theory; electrode measurements of pH in sediments corresponded to titratable H +-content, and pH-changes induced by titration and salt addition were in accord with partitioning theory. These findings suggest that most pH differences observed between colloidal sediments and supernatants are real, not junction artifacts. Guidelines for interpretation of pH measurements on colloids are suggested.