K-Na Discrimination by Porous Filters Saturated with Organic Solvents As Expressed by Diffusion Potentials

The permeability ratio of Millipore filters saturated with organic solvents to K and to Na has been studied by measuring the potential difference across these filters. It was found that with n-octanol, toluene, and chloroform the membranes were more permeable to K(+) than to Na(+), the degree of discrimination being in inverse proportion to the polarity of the solvent. The dependence of NaCl and KCl diffusion potentials upon the concentration gradients across a filter soaked with about 1:1 toluene/n-butanol solution, could be expressed by the constant field equation, if it is assumed that this layer is 6 to 7 times more permeable to K(+) than to Na(+) and that the permeability to Cl(-) is negligible. Elevating the fraction of toluene in n-butanol in the separating phase makes it more selective.