A theoretical model has been developed which relates physically accessible parameters to the formation of a membrane potential. The description is an extension of a theoretical description presented previously by our group, now including divalent cations and ion-pair association. Simulations of the overall membrane potential reveal several factors that may lead to non-Nernstian response curves. For monovalent and divalent cations a reduction in the slope of the response curve (sub-Nernstian response) should virtually always be expected when ion-pair association takes place in the membrane. Ion-pair association of divalent cations and sample anions can lead to a super-Nernstian response. A diffusion potential generally reduces the Nernstian slope of the response curve. In addition, several experimental results are described which illustrate and confirm our theoretical model.
Cobben, P. L. H. M., Cobben, P. L. H. M., Egberink, R. J. M., Bomer, J. G., Bergveld, P., & Reinhoudt, D. (1994). Chemically modified field effect transistors: the effect of ion-pair association on the membrane potentials. Journal of electroanalytical chemistry, 368(368), 193-208. https://doi.org/10.1016/0022-0728(93)03114-5