Fig. 5

Visual interpretation of the impact of reaction parameters on molar activity at the macro- and microscales. During the radiofluorination reaction, precursor molecules are labeled with either the radioactive or non-radioactive forms of fluoride (F-18 and F-19) that are present in the reaction mixture. The resulting products cannot be chemically separated, resulting in a mixture of ¹⁸F- and ¹⁹F-labeled forms of the tracer. a, b At the macroscale, reagents are the dominant source of fluorine-19 contamination. Thus, as reaction volume is increased (a), the fluorine-19 contamination is increased, leading to reduced molar activity. As starting radioactivity is increased (b), radioactivity is increased while there is no significant increase in fluorine-19 contamination, and therefore molar activity is increased. c, d At the microscale, in contrast, reagents add negligible fluorine-19 contamination compared to that from the cyclotron. Therefore, as reaction volume is increased (c), fluorine-19 contamination remains constant, and molar activity is unaffected. Increasing the starting activity (d) increases both radioactivity and fluorine-19 contamination in proportion, leaving the molar activity unchanged