Donnan potential appears as a result of Donnan equilibrium, named after Frederick G. Donnan

Frederick G. Donnan

Frederick George Donnan FRS was an Irish physical chemist who is known for his work on membrane equilibria, and commemorated in the Donnan equilibrium describing ionic transport in cells...

, which refers to the distribution of ion

Ion

An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...

 species between two ionic solution

Solution

In chemistry, a solution is a homogeneous mixture composed of only one phase. In such a mixture, a solute is dissolved in another substance, known as a solvent. The solvent does the dissolving.- Types of solutions :...

s separated by a semipermeable membrane

Semipermeable membrane

A semipermeable membrane, also termed a selectively permeable membrane, a partially permeable membrane or a differentially permeable membrane, is a membrane that will allow certain molecules or ions to pass through it by diffusion and occasionally specialized "facilitated diffusion".The rate of...

 or boundary. The boundary layer maintains an unequal distribution of ionic solute concentration by acting as a selective barrier to ionic diffusion

Diffusion

Molecular diffusion, often called simply diffusion, is the thermal motion of all particles at temperatures above absolute zero. The rate of this movement is a function of temperature, viscosity of the fluid and the size of the particles...

. Some species of ions may pass through the barrier while others may not. The solutions may be gel

Gel

A gel is a solid, jelly-like material that can have properties ranging from soft and weak to hard and tough. Gels are defined as a substantially dilute cross-linked system, which exhibits no flow when in the steady-state...

s or colloid

Colloid

A colloid is a substance microscopically dispersed evenly throughout another substance.A colloidal system consists of two separate phases: a dispersed phase and a continuous phase . A colloidal system may be solid, liquid, or gaseous.Many familiar substances are colloids, as shown in the chart below...

s as well as ionic liquids, and as such the phase boundary between gels or a gel and a liquid can also act as a selective barrier. Electric potential

Electric potential

In classical electromagnetism, the electric potential at a point within a defined space is equal to the electric potential energy at that location divided by the charge there...

 arises between two solutions is called Donnan potential.

Donnan equilibrium is prominent in the triphasic model for articular cartilage

Cartilage

Cartilage is a flexible connective tissue found in many areas in the bodies of humans and other animals, including the joints between bones, the rib cage, the ear, the nose, the elbow, the knee, the ankle, the bronchial tubes and the intervertebral discs...

 proposed by Mow and Ratcliffe, as well as in electrochemical fuel cells and dialysis

Dialysis

In medicine, dialysis is a process for removing waste and excess water from the blood, and is primarily used to provide an artificial replacement for lost kidney function in people with renal failure...

.

The Donnan effect is extra osmotic pressure attributable to cations (Na and K) attached to dissolved plasma proteins.