Effect of the langmuir-type ion adsorption on the membrane potential of a non-charged membrane

Membrane potential is determined by the combination of the properties of ions and of the membrane. There is, therefore, a possibility that the properties of ions can be reflected on the membrane potential more effectively by artificially modifying the membrane properties. In this paper, the membrane is assumed to have no charge but to adsorb cations or anions selectively, and the effect of Langmuir-type adsorption of ions on the membrane potential is investigated theoretically. The variation of the amount of adsorbed ions affects not only the surface potential but also the diffusion potential within the membrane. The membrane potential shows a minimum or a maximum with the variation of the ion concentration in the bulk solution. This phenomenon results from the variation of the amount of ions adsorbed onto the membrane surfaces. Therefore, information on both the adsorption coefficient of a given ion and the amount of saturation of absorption of the ion is obtained from an analysis of the membrane potential. The theory is applied to the analysis of the affinity membrane potential, which can be used for the determination of blood type, and it is shown that the theory is in good agreement with experimental data.