Radio labeling of [18F]altanserin - a microfluidic approach

Introduction: Our aim was the optimization of radiochemical parameters for the microfluidic preparation of [F-18]altanserin. The four main parameters evaluated were (1) precursor concentration, (2) reaction temperature, (3) bolus flow rate through the microreactor and (4) bolus volume. Methods: For the determination of optimal reaction conditions within a flow-through microreactor synthesizer, 5-400 mu L of precursor and dried [F-18]fluoride solution were simultaneously pushed through the temperature-controlled reactor (180-220 degrees C) with defined bolus flow rates of 10-60 mu L/min. Radiochemical incorporation yields (RCIYs) were examined using a thin layer chromatography (TLC) setup and radio- high-performance liquid chromatography (HPLC). Results: Optimum reaction parameters for the microfluidic set-up were determined as following: 220 degrees C, 5-10 mu L/min pump rate per reactant (10-20 mu L/min reaction overall flow rate) and 2 mg/mL precursor concentration in the reaction mixture. Applying these optimized conditions. RCIYs of 53.7 +/- 7.9 were observed for scaled-up preparations. A positive "bolus effect" was observed: applying higher reaction volume resulted in increased RCIYs. Conclusion: This study proved that the reaction bolus volume is an essential parameter influencing the RCIY of [F-18]altanserin. A possible explanation is the inhomogeneous distribution within the reaction volume probably caused by diffusion at the bolus interface. This important finding should be considered an important variable for the evaluation of all novel radiotracers labeled using a flow-through reactor device. (c) 2012 Elsevier Inc. All rights reserved.