Any given protein (antibody) can be separated from other proteins based on its unique physical and chemical properties. Proteins in solution form hydrogen bonds with water through their charged and polar side chain groups. If the protein solvent interaction is prevented, proteins can interact with each other and form aggregates that precipitate out of solution. As the concentration of salt is increased in a solution, the amount of water available to interact with protein is reduced, leading to interaction between hydrophobic groups on different proteins and the formation of a precipitate. Various factors, including the molecular weight of the protein, pH of the solution and temperature can affect the concentration at which a particular protein will precipitate out of solution. Ammonium sulfate is the salt most commonly used to precipitate proteins from solution. Organic, water miscible solvents (ethanol, methanol, acetone) can also be used to differentially precipitate out proteins.

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