The use of outer-sphere complex formation reactions in ion-exchange chromatography: Separation of maleate and fumarate ions

Outer-sphere complex formation reactions have been used to increase the selectivity of ion-exchange separation of maleate and fumarate ions. The stability constants of the maleate and fumarate complexes of tris(ethylenediamine)cobalt(III) and hexa-amminecobalt(III) have been determined at different ionic strengths from the elution volumes and the parameters of the ion-exchanger bed, and the values at I = 0 obtained by extrapolation. They are: log K [Co(en) 3+ 3 + Ma 2−] = 3.33; log K [Co(NH 3) 3+ 6 + Ma 2−] = 3.77; log K [Co(en) 3+ 3 + Fu 2−] = 1.19; log K [Co(NH 3) 3+ 6 + Fu 2−] = 1.99. The two anions can be separated quantitatively.