Evaluation of a Wet Chemistry Method for Isolation of Cyclotron Produced [211At]Astatine

A wet chemistry approach for isolation of At-211 from an irradiated bismuth target is described. The approach involves five steps: (1) dissolution of bismuth target in conc. HNO3; (2) removal of the HNO3 by distillation; (3) dissolution of residue in 8 M HCl; (4) extraction of At-211 from 8 M HCl into DIPE; and (5) extraction of At-211 from DIPE into NaOH. Results from 55 optimized At-211 isolation runs gave recovery yields of approximately 78% after decay and attenuation corrections. An attenuation-corrected average of 26 +/- 3 mCi in the target provided isolated (actual) yields of 16 +/- 3 mCi of At-211. A sixth step, used for purification of At-211 from trace metals, was evaluated in seven runs. In those runs, isolated At-211 was distilled under reductive conditions to provide an average 71 +/- 8% recovery. RadioHPLC analyses of the isolated At-211 solutions, both initial and after distillation, were obtained to examine the At-211 species present. The primary species of At-211 present was astatide, but astatate and unidentified species were also observed. Studies to determine the effect of bismuth attenuation on At-211 were conducted to estimate an attenuation factor (similar to 1.33) for adjustment of At-211 readings in the bismuth target.