Vacuum ultraviolet photon–mediated production of [18F]F2

Abstract

The chemistry of F2 and its derivatives are amenable to facile aliphatic or aromatic substitution, as well as electrophilic addition. The main limitation in the use of [18F]F2 for radiopharmaceutical synthesis is the low specific activity achieved by the traditional methods of production. The highest specific activities, 55 GBq/μmol, for [18F]F2 have been achieved so far by using electrical discharge in the post-target production of [18F]F2 gas from [18F]CH3F. We demonstrate that [18F]F2 is produced by illuminating a gas mixture of neon/F2/[18F]CH3F with vacuum ultraviolet photons generated by an excimer laser. We tested several illumination chambers and production conditions. The effects of the initial amount of [18F]F-, amount of carrier F2, and number of 193-nm laser pulses at constant power were evaluated regarding radiochemical yield and specific activity. The specific activity attained for [18F]F2-derived [18F]NFSi was 10.3 ± 0.9 GBq/μmol, and the average radiochemical yield over a wide range of conditions was 6.7% from [18F]F-. The production can be improved by optimization of the synthesis device and procedures. The use of a commercially available excimer laser and the simplicity of the process can make this method relatively easy for adaptation in radiochemistry laboratories.