Improved production and processing of ⁸⁹Zr using a solution target

Objective: The objectives of the present work were to improve the cyclotron production yield of ⁸⁹Zr using a solution target, develop a practical synthesis of the hydroxamate resin used to process the target, and develop a biocompatible medium for ⁸⁹Zr elution from the hydroxamate resin. Methods: A new solution target (BMLT-2) with enhanced heat dissipation capabilities was designed by using helium-cooled dual foils (0.2mm Al and 25μ Havar) and an enhanced water-cooled, elongated solution cavity in the target insert. Irradiations were performed with 14MeV protons on a 2M solution of yttrium nitrate in 1.25M nitric acid at 40-μA beam current for 2h in a closed system. Zirconium-89 was separated from Y by use of a hydroxamate resin. A one-pot synthesis of hydroxamate resin was accomplished by activating the carboxylate groups on a carboxymethyl cation exchange resin using methyl chloroformate followed by reaction with hydroxylamine hydrochloride. After trapping of ⁸⁹Zr on hydroxamate resin and rinsing the resin with HCl and water to release Y, ⁸⁹Zr was eluted with 1.2M K₂HPO₄/KH₂PO₄ buffer (pH3.5). ICP-MS was used to measure metal contaminants in the final ⁸⁹Zr solution. Results: The BMLT-2 target produced 349±49MBq (9.4±1.2mCi) of ⁸⁹Zr at the end of irradiation with a specific activity of 1.18±0.79GBq/μg. The hydroxamate resin prepared using the new synthesis method showed a trapping efficiency of 93% with a 75mg resin bed and 96-97% with a 100-120mg resin bed. The elution efficiency of ⁸⁹Zr with 1.2M K₂HPO₄/KH₂PO₄ solution was found to be 91.7±3.7%, compared to >95% for 1M oxalic acid. Elution with phosphate buffer gave very small levels of metal contaminants: Al=0.40-0.86μg (n=2), Fe=1.22±0.71μg (n=3), Y=0.29μg (n=1). Conclusions: The BMLT-2 target allowed doubling of the beam current for production of ⁸⁹Zr, resulting in a greater than 2-fold increase in production yield in comparison with a conventional liquid target. The new one-pot synthesis of hydroxamate resin provides a simpler synthesis method for the ⁸⁹Zr trapping resin. Finally, phosphate buffer elutes the ⁸⁹Zrfrom the hydroxamate resin in high efficiency while at the same time providing a more biocompatible medium for subsequent use of ⁸⁹Zr.