in ion exchange chromatography
https://doi.org/10.1351/goldbook.S05566
The equilibrium
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: kMg/Ca=[Mg]S/[Ca]S[Mg]M/[Ca]M Mg2+Ca2+ Exchange: SO42−Cl kSO4/Cl=[SO4]S/[Cl]S2[SO4]M/[Cl]M2 In the above equations subscript S refers to the
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 kA/B depends on the choice of the concentration scales in the
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
(kA/Ba) is calculated in a way identical to the
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
.
Sources:
PAC, 1993, 65, 2373. (Nomenclature for liquid-liquid distribution (solvent extraction) (IUPAC Recommendations 1993)) on page 2385 [Terms] [Paper]
PAC, 1993, 65, 819. (Nomenclature for chromatography (IUPAC Recommendations 1993)) on page 857 [Terms] [Paper]