Separation of ²¹³Bi via an inverse ²²⁵Ac/²¹³Bi radionuclide generator based on sulfonated carbon materials

Bismuth-213 (²¹³Bi) is an alpha-emitting radioisotope with large potential in nuclear medicine for cancer treatment. This study evaluated sulfonated carbon materials for use in inverse ²²⁵Ac/²¹³Bi radionuclide generators. The synthesis protocol was optimized with regard to the pyrolysis temperature and sulfonation conditions. The materials were characterized with regard to the pore size distribution, the nature of the functional groups and the zeta potential. The separation of Bi³⁺, La³⁺ (as surrogate for ²²⁵Ac) and Ac³⁺ using the sulfonated carbon materials were examined by batch experiments, as a function of different parameters (e.g. pH, salt concentration, solid-to-liquid ratio, and contact time). The sulfonated carbon materials exhibited a high selective uptake of Bi³⁺ in the presence of high salt concentrations at low pH. Inversely, the sorption capacity for La³⁺ and Ac³⁺ onto the sulfonated carbon materials decreased with increasing salt concentrations and decreasing pH. Batch desorption results showed that a high percentage of Bi³⁺ can be eluted from sulfonated carbon materials by HCl, NaI, or NaCl solutions. More importantly, the sulfonated carbon materials showed high levels of resistance against radiolysis, fast sorption kinetics, good durability, and recyclability. The evaluation of the different materials enabled a better understanding of the sorption mechanisms of Bi³⁺ and Ac³⁺ onto these sulfonated carbon materials. Based on the separation performance, the most suitable sorbent was examined using column chromatography. The ²¹³Bi yield from the inverse generator reached 94% in 1 ml of 1M HCl with an ²²⁵Ac impurity of less than 0.04 % of the eluted ²¹³Bi activity. Experiments also revealed that a guard column with AG MP-50 reduced the impurity of ²²⁵Ac without affecting the ²¹³Bi yield. These findings indicate that the sulfonated carbon materials are promising adsorbents in inverse ²²⁵Ac/²¹³Bi radionuclide generators for the production of high-purity ²¹³Bi for medical applications.