Transport of ions against their concentration gradient across cation-exchange membranes with very small mechanical permeabilities

In two sets of experiments the transport of potassium ions and of potassium and lithium ions against their concentration difference between two solutions across a cation-exchange membrane is being investigated. The driving forces of the ion transport are a concentration gradient and an electric potential gradient within the membrane separating these solutions. The membrane has a small mechanical permeability so that the contribution of convection to the ion transport can be neglected. In the stationary state of the system, an increase of the concentration of potassium or potassium and lithium ions up to a factor of 4 above the concentration of these ions in the initial state is observed in one outside solution of the membrane. In the initial state the concentrations of the alkali ions are the same in both outside solutions. During the simultaneous transport of potassium and lithium ions, there is a certain period of time between the initial and the stationary state of the system in which a partial separation of potassium and lithium ions is observed. The experimental results are discussed in terms of the equation of ion transport across membranes with narrow pores. © 1968, American Chemical Society. All rights reserved