Minimization of the amount of Kryptofix 222 - KHCO3 for applications to microscale 18F-radiolabeling

Conversion of aqueous [18F]fluoride to reactive [18F]fluoride is an important first step in the radiosynthesis of 18F-labeled compounds by nucleophilic substitution. A versatile method for the rapid preparation of reactive [18F]fluoride by the combined use of an Oasis MAX cartridge and a methanolic solution of the Kryptofix 222-KHCO3 complex (K.222/KHCO3) was developed. The latter amount was optimized with the aim to keep it as low as possible while achieving recovery yields of [18F]fluoride comparable to those attained with the commonly used QMA cartridge. Thus, a 97% recovery yield was obtained with just 2 µmol of K.222/KHCO3 methanolic solution (10 mM, 200 µL) within 7 min. This result allowed in turn to optimize the microscale radiosynthesis of [18F]FDG. Moreover, the method was successfully applied to the 100 µL-scale 18F-substitution reactions of several precursors.