Impurities in the [18O]water target and their effect on the yield of an aromatic displacement reaction with [18F]fluoride.

Fluorine-18 in the form of fluoride ion has widespread utility in PET radiochemistry. This paper explores the effect of possible metal ion contamination of the water on the yield of the displacement of a nitro group off of dinitrobenzene by fluoride has been investigated as a model reaction for fluoride displacement. The metal ions were found to have a profound effect if they were at the level of the carbonate added to the synthetic procedure. The yields from the reaction are best fit by a model in which the metal ions complex the carbonate ion and thus reduce the pH which in turn reduces the efficiency of the reaction. The formation of [18F]fluoroacetate in the target was explored as a mode for making the fluoride in the target unreactive. It was found that essentially no fluoroacetate was formed under our irradiation conditions. The sources of carrier fluoride were examined. It was found that carrier fluoride was introduced during the transfer of water into and out of the target and not during the irradiation.