A flow-through system is described for rapid purification of [18F]fluoride for nucleophilic substitution reactions. It depends on generation of [18F]fluorotrimethylsilane from aqueous 18F solutions and subsequent collection of the gas and its hydrolysis by base in near anhydrous acetonitrile. Potassium t-butoxide plus Kryptofix 2.2.2 was found to be a more effective base than K2CO3 plus Kryptofix or than tetraethylammonium hydroxide. The procedure takes 2-3 min and is thus faster than controlled removal of water from [18F]fluoride by evaporation. The trapped and hydrolyzed 18F was used in several nucleophilic substitution reactions. The flow-through system is also convenient for recovery of fluoride from impure and otherwise unreactive solutions, including residues from large scale 18F syntheses, and can thus lead to more efficient use of 18F where production of the radionuclide is limited.
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