Distribution Ratio:

It should be remembered that we should not speak of a resin to pick up a certain ion without noting that there is another ion in the resin phase. It is actually the tendency of an ion exchanger to pick up A⁺ at the expense of B⁺. This tendency of the exchanger to take up A⁺ will be different if the resin contains other ions C⁺ instead of B⁺. Thus, we can prepare a resin containing a certain counter ion and then compare a series of other ions containing this counter ion as a reference. For the ions in this series, we may simply mention distribution ratios. Distribution ratio simply expresses the partitioning of ion between the solution and the resin phases.

D = Conc. of an ion in the re sin/Conc. of the same ion in the solution

The conventional units are

D =  (Amount / kg of dry re sin)/(Amount / Litre of solution)

The amount word, in milligram, moles or whatever might be is proper since the units cancel in calculating the D ratio.