Preferred Label : selectivity coefficient;
Detailed label : selectivity coefficient in ion exchange chromatography, kA/B;
IUPAC definition : 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: \[k_{{Mg}/{Ca}} \frac{{[Mg]}_{{S}}/{[Ca]}_{{S}}}{{[Mg]}_{{M}}/{[Ca]}_{{M}}}\]
Mg sup 2 /sup – Ca sup 2 /sup Exchange: SO sub 4 /sub sup 2 /sup – Cl sup class
minus /sup \[k_{{SO}_{4}/{Cl}} \frac{{[}{SO}_{4}{]}_{{S}}/{[Cl]}_{{S}} {2}}{{[}{SO}_{4}{]}_{{M}}/{[Cl]}_{{M}}
{2}}\] 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.;
Origin ID : S05566;
See also
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: \[k_{{Mg}/{Ca}} \frac{{[Mg]}_{{S}}/{[Ca]}_{{S}}}{{[Mg]}_{{M}}/{[Ca]}_{{M}}}\]
Mg sup 2 /sup – Ca sup 2 /sup Exchange: SO sub 4 /sub sup 2 /sup – Cl sup class
minus /sup \[k_{{SO}_{4}/{Cl}} \frac{{[}{SO}_{4}{]}_{{S}}/{[Cl]}_{{S}} {2}}{{[}{SO}_{4}{]}_{{M}}/{[Cl]}_{{M}}
{2}}\] 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.