Fluorine‐18 labelling of lower fatty acid esters by heterogeneous exchange on gas chromatographic columns

Abstract

Abstract Fluorine‐18 produced via the reaction chain 6 Li(n,α)t, 16 O(t,n) 18 F by reactor irradiation of Li 2 CO 3 was directly recovered in carrier‐free form with a 90% yield by repeated extractions with water. A simple apparatus was used for simultaneous extraction and fast loading of an exchange resin with 18 F . Dowex 1×4 in the acetate form was found to be best suited for a gas phase 18 F ‐for‐Br exchange in α‐bromofatty acid esters. The 18 F ‐loaded exchange resin was brought into a gas chromatographic column followed by an analytical column for the separation of the 18 F ‐labelled product from the unchanged bromine compound. The dynamic technique combines synthesis and purification and allows a fast and carrier‐free production of 18 F ‐α‐fluorofatty acid esters with boiling points up to about 300 °C. α‐fluoroacetic acid ethyl ester and α‐fluorovaleric acid methyl ester have been labelled carrier‐free with yields of 64% (at 170 °C) and 39% (at 190 °C), respectively. Kinetic studies on the yield determining factors have also been carried out.