Separation of calcium-48 isotope by crown ether chromatography using ethanol/hydrochloric acid mixed solvent

•Benzo-18-crown-6 ether resin was synthesized for chromatographic separation of Ca-48.•Ca ions are adsorbed on the resin in concentrated HCl/ethanol mixed solution.•Ca adsorption is controlled by HCl added to ethanol at any mixing ratios.•Heavy isotope Ca-48 is enriched at the front boundary of chromatogram.•Flame photometry was applied to the measurement of Ca concentration.