Diafiltration is a dilution technique that is used to remove or separate permeable molecules such as small proteins, salts, and solvents from a solution. The separation is based on the molecular size of the components and involves using ultrafiltration membranes to selectively retain larger molecules while allowing smaller molecules such as salts and solvents to pass through. The aim is to replace, remove, or dilute the concentration of salts or solvents from solutions containing nucleic acids, peptides, proteins, and other biomolecules. 

The diafiltration process combines dilution and filtration, as buffer solution or demineralized water is added to the concentrate to maintain the concentration of target products while gradually washing out unwanted compounds.