Since proteins differ markedly in their solubilities at high ionic strength, salting-out is a very useful procedure to assist in the purification of a given protein. The commonly used salt is ammonium sulfate, as it is very water-soluble, forms two ions high in the Hofmeister series.It is generally used as a saturated aqueous solution which is diluted to the required concentration, expressed as a percentage concentration of the saturated solution (a 100% solution).his is usually done by adding solid ammonium sulfate, but calculating how much ammonium sulfate to add to a solution at one concentration to achieve a desired higher concentration is tricky, since addition of ammonium sulfate significantly increases the volume of the solution.