Dialysis and reverse osmosis

Dialysis is a separation process with many applications in clinical, biochemical and environmental analysis. Donor and acceptor solutions are separated by a membrane, which is permeable to one or more solutes. When the solutions have different solute activities, a diffusional transport from the higher to the lower activity a (a = cf, where c is the concentration and f the activity coefficient) through the membrane takes place. The main driving force for the diffusion of small molecules or ions is their concentration gradient. In most cases, dialysis is employed to retain large molecules while exchanging or eliminating small ones.