SEPARATION OF CARRIER-FREE HO-166 FROM NEUTRON-IRRADIATED DYSPROSIUM TARGETS

Holmium-166 (Ho-166, t(1/2) = 26.4 h) is utilized in radiotherapeutic applications such as radioimmunospecific pharmaceuticals, bone marrow ablation, and radiation synovectomy. High specific activity Ho-166 can be obtained from the decay of dysprosium-166 (Dy-166, t(1/2) = 81.5 h ). Dysprosium-166 is produced by the Dy-164[n,gamma]Dy-165[n,gamma]Dy- 166 reaction in a nuclear reactor. The applicability of reversed phase ion-exchange chromatographic methods was demonstrated for the separat ion of carrier-free Ho-166 from milligram quantities of (Dy2O3)-Dy-164 irradiated targets. An efficient and quantitative separation was achi eved utilizing a metal-free HPLC system with Dowex AG 50WX12 or Aminex -A5 cation exchangers and alpha-hydroxyisobutyric acid (alpha-MIBA) as the eluent (0.085 M, pH 4.3 adjusted with NH4OH). The Aminex-A5 colum n gave a separation factor of similar to 10(3) between Ho and Dy. Subs equent to the acidic destruction of the Ho-HIBA complex, Ho3+ was furt her purified on a small cation-exchange column from acidic chloride so lutions. The separation was achieved within 2 h, with a 95% overall ra diochemical yield for carrier-free Ho-166 with a DY breakthrough of <0 .1%.