The thermodynamic equilibrium between charged colloids and an electrolyte reservoir is named after Frederic Donnan who first published on it one century ago (Donnan 1911 Z. Electrochem. 17 572). One of the intriguing features of the Donnan equilibrium is the ensuing osmotic equation of state which is a nonlinear one, even when both colloids and ions obey Van 't Hoff's ideal osmotic pressure law...

Free metal ions in aqueous and terrestrial systems strongly influence bioavailability and toxicity. Most analytical techniques determine the total metal concentration, including the metal ions bound by dissolved organic matter. Ion activity can be measured with ion-specific electrodes (ISEs) for some metals, but an electrode for Zn is not commercially available. As a result, very few data are a...

This paper discusses the little-known fact that Donnan’s equilibrium criteria established over 100 years ago neglected coupling between ion concentrations and osmotic pressure. Such can be treated based on general thermodynamic considerations including solvent equilibrium, leading to a membrane potential consists of not only classical Donnan term but also an additional due pressure, existence e...