Mass dependence of calcium isotope fractionations in crown-ether resin chromatography

Benzo 18-crown-6-ether resin was synthesised by the phenol condensation polymerisation process in porous silica beads, of which particle diameter was ca 60μ Calcium adsorption chromatography was performed with the synthesised resin packed in a glass column. The effluent was sampled in fractions, and the isotopic abundance ratios of ⁴²Ca, ⁴³Ca, ⁴⁴Ca, and ⁴⁸Ca against ⁴⁰Ca were measured by a thermo-ionisation mass spectrometer. The enrichment of heavier calcium isotopes was observed at the front boundary of calcium adsorption chromatogram. The mass dependence of mutual separation of calcium isotopes was analysed by using the three-isotope-plots method. The slopes of three-isotope-plots indicate the relative values of mutual separation coefficients for concerned isotopic pairs. The results have shown the normal mass dependence; isotope fractionation is proportional to the reduced mass difference, (M – M′)/MM′, where M and M′ are masses of heavy and light isotope, respectively. The mass dependence clarifies that the isotope fractionations are originated from molecular vibration. The observed separation coefficient ? is 3.1×10^?3 for the pair of ⁴⁰Ca and ⁴⁸Ca. Productivity of enriched ⁴⁸Ca by crown-ether-resin was discussed as the function of the separation coefficient and the height equivalent to the theoretical plate.