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

Abstract

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.

Keywords:

• Gallium
• indium
• chemical isotope effects
• ligand exchange
• ion exchange chromatography

ACKNOWLEDGMENT

The authors express their gratitude to E. Bulska and I. A. Wysocka (Warsaw University), and W. Skwara (Institute of Nuclear Chemistry and Technology) for their help in the ICP-MS and AAS analyses.