The ratio of activities of a solute, A in an aqueous/organic system will remain constant and independent of the total quantity of A (hence ), so at any given temperature:
Distribution constants are useful as they allow the calculation of the concentration of remaining analyte in the solution, even after a number of solvent extractions have occurred. They also provide guidance in choosing the most efficient way to conduct an extractive separation.
Thus, the concentration of A remaining in an aqueous solution after i extractions with an organic solvent can be found using:
(where [A] is the concentration of A remaining after extracting V millilitres of solution with the original concentration of [A] with i portions of the organic solvent, each with a volume of V).