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

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