https://doi.org/10.1351/goldbook.S05566
The equilibrium Mg2+ – Ca2+ Exchange: SO42− – Cl− In the above equations subscript S refers to the depends on the choice of the concentration scales in the ) is calculated in a way identical to the
coefficient
obtained by application of the law of mass action to ion exchange
and characterizing quantitatively the ability of an ion exchanger
to select one of two ions present in the same solution. The ions involved in the exchange should be specified as subscripts. Examples: Exchange: ion exchanger
('stationary phase') and M to the external solution ('mobile phase'). For exchanges involving counter-ions
differing in their charges, the numerical value of ion exchanger
and the external solution (molal
scale, molar scale, mole fraction
scale, etc.). Concentration units must be clearly stated for an exchange of ions of differing charges. The corrected selectivity
coefficient
(selectivity
coefficient
except that the concentrations in the external solutions are replaced by activities. This term should not be used as a synonym for separation factor
.