Calcium ion selectivity and isotope effects studied by using benzo-18-crown-6 resins

The chromatography experiments using benzo-18-crown-6 resin were carried out to study isotope effects in calcium adsorption. By the elution technique with hydrochloric acid solution, it was found that the adsorption of calcium depends on the concentration of hydrochloric acid in solution and that 9 M HCl concentration is the appropriate condition for the adsorption of calcium to the cavity of benzo-18-crown-6 of which cavity size is a little larger than the diameter of calcium ion. Thereafter, the isotope fractionation of calcium in the complex formation reaction with 18-crown-6 ether was investigated by using the breakthrough technique of chromatography with above-mentioned synthesized resin and 9 M hydrochloric acid solution. The observed isotope separation coefficient ε=α−1 was 1.9 × 10−3 for the isotopic pair 40Ca/48Ca.