FIGURE 4. (A) Reaction scheme shows radiosynthesis of ¹⁸F-N-BOC-nifrolidine and HPLC purification of ¹⁸F-N-BOC-nifrolidine using C₁₈ reverse-phase semipreparative column eluted with 60% acetonitrile/0.1 mol/L ammonium formate at flow rate of 4.0 mL/min. Retention time of ¹⁸F-N-BOC-nifrolidine was 11.5 min. (B) Reaction scheme shows radiosynthesis of ¹⁸F-nifrolidine and HPLC purification of ¹⁸F-nifrolidine using C₁₈ reverse-phase semipreparative column eluted with gradient of 0.1 mol/L ammonium formate (100%)/acetonitrile (0%) at time 1 min to 0.1 mol/L ammonium formate (40%)/acetonitrile (60%) at time 35 min with flow rate of 4.0 mL/min. Retention time of ¹⁸F-nifrolidine was 22 min. UV = ultraviolet.