Separation of rubidium isotopes by extraction chromatography with a retaining ion strategy

Currently, separation of rubidium isotopes relies predominantly on electromagnetic methods. However, operational complexity and prohibitive equipment costs severely limit its broader applicability and industrial scalability. In this study, we propose a novel extraction chromatography method for rubidium isotope separation of using t-BAMBP-impregnated resin as the stationary phase and introducing K⁺ as retaining ion to increase the separation coefficient between ⁸⁵Rb⁺ and ⁸⁷Rb⁺ during elution process. Compared to conventional electromagnetic separation, this new extraction chromatography method features a simple operating condition and lower processing cost for rubidium isotope separation. According to the Stokes-Einstein relation, the lighter mass of ⁸⁵Rb⁺ has a smaller effective hydrodynamic radius and consequently a higher diffusion coefficient compared to ⁸⁷Rb⁺. This intrinsic kinetic difference, combined with the subtle disparity in their distribution ratios on the t-BAMBP-impregnated resin, leads to a faster migration rate of ⁸⁵Rb⁺ over ⁸⁷Rb⁺ during chromatographic elution. The introduction of K⁺ as a retaining ion further prolongs the retention time and increases the plate number of adsorption-desorption cycles, thereby amplifying the longitudinal diffusion advantage of ⁸⁵Rb⁺. Under the optimized conditions, this synergistic effect from introduction of K⁺ as a retaining ion yields a maximum single-column separation factor of 1.00534. The current work achieves a breakthrough in rubidium isotope separation, which is beneficial for future industrial applications.