Donnan equilibrium

https://doi.org/10.1351/goldbook.D01831
The equilibrium characterized by an unequal distribution of diffusible ions between two ionic solutions (one or both of the solutions may be gelled) separated by a @MT06878@ which is impermeable to at least one of the ionic species present, e.g. because they are too large to pass through the pores of the @MT06878@. The @MT06878@ may be replaced by other kinds of restraint, such as @GT07621@, the field of gravity, etc., which prevent some ionic components from moving from one phase to the other, but allow other components to do so.
Source:
PAC, 1972, 31, 577. (Manual of Symbols and Terminology for Physicochemical Quantities and Units, Appendix II: Definitions, Terminology and Symbols in Colloid and Surface Chemistry) on page 619 [Terms] [Paper]