Interferences double charged ions

The sign will be + for cation-selective electrodes and - for those that are anion-selective. To be predominantly responsive to the concentration Ci, the factor Kij must be small. Where liquid membrane ion-selective electrodes responsive primarily to double-charge ions are concerned, and for interference by single-charge ions, equation (1) modifies to ... 

In the case of a thin and dense double layer, the electric field is distorted by the particles in the fluid because of the (usually) larger particle size and the compactness of the double layer (von Smoludiowski, 1917, 1921). The principal result of this is that the electrophoretic friction, F3, is considerably reduced because the oppK>sitely charged ions in the path of the moving particle do not interfere with the particle s motion, and those ions slightly tangential to the partide contribute little to the friction. This increases the mobility of these partides. Here the electrophoretic mobility is derived using Poisson s equation ... 

---