Designing metal oxide-based stationary phases for the separation of Ac-225 and Bi-213 for biomedical applications

²¹³Bi is a promising radiopharmaceutical for alpha-therapy because of its suitable half-life and well-known chelation chemistry. The biggest hurdle, however, is the ²¹³Bi production, which is now far from sufficient to implement this isotope in targeted alpha therapy on a large scale. The most commonly used generator for the separation of ²²⁵Ac and ²¹³Bi is based on AG MP-50. This is a macroporous strong acid cation exchange resin composed of sulphonic acid groups attached to a styrene divinylbenzene copolymer backbone. The AG MP-50 generator has a high yield (>76 % ²¹³Bi), a very low breakthrough of ²²⁵Ac (<210-5 %) and the ²¹³Bi elution is very fast (2-3 min). Despite these great advantages, the main disadvantage is its low radiation stability. The organic backbone and especially the link with the functional group is very susceptible to radiation damage, such that in normal operation conditions the performance of the generator will substantially decrease. On the other hand, inorganic materials are known to be more resistant against radiation. Therefore, this contribution presents the study of surface modified inorganic materials and their performance towards ²²⁵Ac/²¹³Bi separation. The materials under investigation are titania and zirconia, which are modified with phosphoric acid groups. Different analytical techniques such as zeta potential and ICP-MS are utilized to characterize the surface modification of the inorganic materials. Furthermore, the modified materials are subjected to a 'cold sorption' test. Via this method, sorption properties such as separation efficiency, leaching stability and sorption capacity are evaluated by means of non-radioactive solutions of La and Bi. Ultimately, the actual ²²⁵Ac/²¹³Bi sorption properties of the phosphoric acid-modified materials will be tested in a radiochemical laboratory.