Separation of Gallium and Indium Isotopes by Cation and Anion Exchange Chromatography

Ion exchange chromatography was applied to study chemical isotope effects of gallium and indium in ligand exchange reactions. A strongly acidic cation and a strongly basic anion exchange resin were used as a solid phase, and aqueous HCl as a liquid phase. On the cation exchanger, the light isotope 69Ga was enriched at the front part of the elution band and the heavy isotope 71Ga at the end part. Instead, the light 113In isotope was enriched at the end part, and the heavy isotope 115In at the front part. The isotope separation factor ϵ is equal to 3.3 × 10–5 for gallium and 2.0 × 10–4 for indium. On the anion exchanger, the heavy gallium isotope was enriched at the front part, whereas the heavy indium isotope at the end part of the band, with ϵ equal to ∼10–3 and 1.7 × 10–4, respectively. This pattern of enrichment is caused by stronger Ga3+–OH2 than Ga3+–Cl− bond, and by inverse order of bond strength for indium. In the displacement method, gallium and indium on anion exchanger also show opposite enrichment of their isotopes, but the ϵ values (1.5 × 10–2 for gallium and 5 × 10–3 for indium) are greater than those found in the elution method, probably due to much higher concentrations of the metals.