Calcium Isotope Effect in Calcium Ion Exchange with a Fluid Phase Containing a Macrocyclic Compound

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Abstract
The separation coefficient for calcium isotope exchange with a macrocyclic polyether was measured by ion exchange chromatography. The isotopic enrichment proceeds according to the chemical exchange reaction: where L represents the macrocyclic polyether 18-crown-6. The observed -separation coefficient for the calcium 40/44 isotope pair, ε(40/44), was 4.9×10−4 (±1.3×10, 95% C.L.) with calcium-40 enriched in the fluid phase. A sulfonic acid resin was used with a fluid phase consisting of a 70/30 volume percent mixture of ethanol and water. The isotope effect was smaller than metal-crown isotope effects reported in the literature, and possible reasons for this are discussed.