Donnan exclusion

https://doi.org/10.1351/goldbook.DT06889
Reduction in concentration of mobile ions within an ion exchange membrane due to the presence of fixed ions of the same sign as the mobile ions.
Source:
PAC, 1996, 68, 1479. 'Terminology for membranes and membrane processes (IUPAC Recommendations 1996)' on page 1488 (https://doi.org/10.1351/pac199668071479)