Permselectivity for specific ions

Ion Exchange Membranes having Permselectivity for Specific Ions... 

Many attempts to prepare ion exchange membranes having permselectivity for specific ions and to find electrodialysis methods to achieve such a purpose have been made. In this chapter, studies on the modification of ion exchange membranes and electrodialysis methods to permeate specific ions through the membrane, mainly in electrodialysis, are explained. 

As mentioned in Chapter 5, ion exchange membranes have no permselectivity for specific ions. If an ion exchange membrane had permselectivity for specific ions, separation of ions with the same charge would be possible by electrochemical potential, which would be a remarkable contribution to industry. In the anion exchange membrane, permselectivity between anions is reported to be controlled by the difference of the hydrophilicity of the membrane. New methods other than controlling the hydrophilicity of the membrane should be found on the basis of another mechanism. 

Sata, T. (1994) Studies on ion exchange membranes with permselectivity for specific ions in electrodialysis. Journal of Membrane Science, 93, 117-135. 

Membrane Efficiency The permselectivity of an ion-exchange membrane is the ratio of the transport of electric charge through the membrane by specific ions to the total transport of electrons. Membranes are not strictly semipermeable, for coions are not completely excluded, particularly at higher feed concentrations. For example, the Donnan eqmlibrium for a univalent salt in dilute solution is ... 

Permselectivity is the ability of a membrane to allow a high flux of one chemical species (typically the analyte) while reducing or eliminating the flux of other species (chemical or sensor interferences). An extreme example of permselectivity is the liquid polymer membranes used in ion selective electrodes. The ionophores contained in these membranes bind selectively to a specific ion. However, this binding is often so strong that the diffusion constant for these ions through the membrane is vanishingly small [15]. 

---