Bi-ionic potential

When a cation exchange membrane separates two different electrolyte solutions with different counter-ions such as AY and BY, a bi-ionic potential arises.13 The simplest system is 

An example is where one surface of a cation exchange membrane contacts sodium chloride solution and other side contacts potassium chloride solution. The bi-ionic potential is the sum of the Donnan potential at both membrane-solution interfaces and the diffusion potential through the membrane. For cation exchange membranes, the membrane surface becomes positive on contact with the solution 

When one surface of a cation exchange membrane contacts potassium chloride solution and the other side sodium chloride solution, potassium ions, in general, more selectively adsorb with cation exchange membranes and more easily diffuse through the membrane. Thus, the membrane surface in contact with potassium chloride solution becomes negative. 

The bi-ionic potential basically provides a measure of permselectivity between ions with the same charge through the ion exchange membrane. 

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Cells of the type in Scheme 11 represent the simplest case of cells with a bi-ionic potential [3]. Hence, in the case of a larger number of ions transferred through the organic phase a multi- or polyionic potential should be considered. Liquid ion-selective electrodes operate on the basis of cells of the type in Scheme 10 their selectivity can be examined with the use of Scheme 11 and polyionic cells. 

Bi-Ionic Potentials (B.I.P s). If a membrane separates two salt solutions with two different counterions, but the same co-ion, the corresponding membrane potential is called bi-ionic potential. For the calculation of the B.I.P. this is split in a diffusion potential and two Donnan potentials. The diffusion potential can be calculated by proceeding from equation (37). 

Bi- and Multi-Ionic Potential. When correction terms are neglected, the formula for the bi-ionic potential reads ... 

K. Sollner, The origin of bi-ionic potentials across porous membranes of high ionic selectivity. I. The bi-ionic potential and the mechanism of its origin the various factors that determine the sign and the magnitude of the bi-ionic potential the simplest chains in which bi-ionic potentials arise systems with critical ions of the same size of different adsorbability, J. Phys. Colloid Chem., 1949, 53, 1211-1239. 

The bi-ionic potential can be measured using a similar two-compartment cell to that shown in Figure 4.4. The effect on the potential of diffusion boundary layers at the membrane surfaces should be removed by either agitating or circulating the solutions. 

D.K. Hale and K.P. Govindan, Bi-ionic potentials with sulfonic and phosphonic acid cation-exchange membranes,./ Electrochem. Soc., 1969, 116, 1373-1381. 

S. Tran, L. Dammak, C. Larchet and B. Auclair, Bi-ionic potential through a cation exchange membrane separating two electrolytes at different concentrations, Electro-chim. Acta, 1999, 44, 2515-2521 M. Tasaka and H. Sugioka, Dependence on salt concentration of bi-ionic potential across polystyrene sulfonic-acid-type membranes, J. Membr. Sci., 1988, 38, 27-37. 

R. Kiyona, A. Kuwashita, T. Nishizawa, M. Yamauchi and M. Tasaka, Bi-ionic potential across poly(4-vinylpyridine-co-styrene) membranes, Kaisui Gakkaishi (Bull. Sea Water Sci. Jpn.), 1993, 47, 369-374. 

Y. Toyoshima and H. Nozaki, Bi-ionic potential across charged membranes, J. Phys. Chem., 1970, 74, 2704-2710. 

The ion selectivity of gramicidin channels can be measured either from bi-ionic potentials [21] or from the conductance ratios of single channels [16]. Both approaches give the same selectivity sequence and do not depend either on membrane composition or thickness. The ion sequence is ... 

The non-equilibrium effects on the selectivity determination can be eliminated by measuring the bi-ionic potential in the following cell (49, 50) ... 

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