ˈdänən- noun
Usage: usually capitalized D
Etymology: after Frederick G. Donnan died 1956 British chemist and physicist
: the ionic equilibrium reached in a solution of an electrolyte whose ions are diffusible through a semipermeable membrane but are distributed unequally on the two sides of the membrane because of the presence of a nondiffusible colloidal ion (as a protein ion) on one side of the membrane