Minimization of the amount of Kryptofix 222 - KHCO 3 for applications to microscale 18 F-radiolabeling.

Conversion of aqueous [18 F]fluoride to reactive [18 F]fluoride is an important first step in the radiosynthesis of18 F-labeled compounds by nucleophilic substitution. A versatile method for the rapid preparation of reactive [18 F]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 [18 F]fluoride comparable to those attained with the commonly used QMA cartridge. Thus, a 97% recovery yield was obtained with just 2µmol of K.222/KHCO3 methanolic solution (10mM, 200µL) within 7min. This result allowed in turn to optimize the microscale radiosynthesis of [18 F]FDG. Moreover, the method was successfully applied to the 100µL-scale18 F-substitution reactions of several precursors.