44Ti/44Sc radionuclide generators are of interest for molecular imaging. The 3.97 h half-life of 44Sc and its high positron branching of 94% may stimulate the application of 44Sc labelled PET radiopharmaceuticals. However, both 44Ti production and 44Ti/44Sc generator design represent challenges for basic radiochemistry.
About 5 mCi (185 MBq) of 44Ti were obtained via the Sc(p, 2n) nuclear reaction. 44Ti was separated from 1.5 g of massive scandium targets in multi-step procedures, including exchange chromatography on cation exchange resin (AG 50W-X8, 200−400 mesh, H+-form). In order to design a robust 44Ti/44Sc generator concept, distribution coefficients of Ti(IV) and Sc(III) on both AG 1-X8 (200−400 mesh, Cl--form) and AG 50W-X8 (200−400 mesh, H+-form) resins eluted with HCl and HCl/H2C2O4 solution of various concentrations were investigated systematically. Optimal conditions for efficient separations of both radionuclides have been determined for AG 1-X8 resin and mixtures of 0.07 M HCl and 0.005 M H2C2O4.
A 5 mCi generator was prepared on an AG 1-X8 column (H=150 mm, D=3 mm, V0=0.55 mL). The system achieved elution of 180 MBq 44Sc in 20 mL of eluate solution. The breakthrough of 44Ti is 90 Bq. This corresponds to an excellent separation factor of 2×106.
In the context of long-term stability of 44Ti/44Sc generators, a “reverse” type of washing steps after each elution using 0.07 M HCl/0.005 M H2C2O4 mixtures appeared to be essential.
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