Cations from cyclotron target solutions can impede chelation of fluorine-18 radiolabeled aluminum-fluoride

Coordination of fluorine-18 to aluminum renders the positron emitting radionuclide a pseudo-radiometal. This permits its use in chelators commonly used for theranostics applications while exploiting the favourable half-life, high positron branching ratio, and small positron range. As for other tracer-level chelations, interfering metal cations will diminish radiochemical yields. While translating an automated and validated [ 18 F]FAPI-74 radiosynthesis, we were initially unsuccessful. While troubleshooting all aspects of the radiosynthesis (e.g., human error, equipment failure, materials), the ultimate root cause was determined to be cations present in the cyclotron target solution. After passing the fluorine-18 containing target effluent through a commercial cation exchange cartridge, radiochemical yields returned to reported and expected values. The reduction of cations was confirmed by inductively coupled plasma mass spectrometry. We further confirmed the exclusion of these chemical impurities did not impact other radiofluorination reactions in our facility, thus capturing the cations is likely an additional precaution for clinical manufacturing of any fluorine-18 radiotracer.