Conversion of no-carrier-added [C-11]carbon dioxide to [C-11]carbon monoxide on molybdenum for the synthesis of C-11-labelled aromatic ketones

A new method for the efficient conversion of no-carrier-added [C-11]carbon dioxide into [C-11]carbon monoxide is described. [C-11]Carbon dioxide produced by proton bombardment of ultra high purity nitrogen is pre-concentrated in a cryo trap and then passed through a quartz tube filled with a mesh of thin molybdenum wire heated to 850 degrees C. [C-11]Carbon dioxide readily reacts with molybdenum to form [C-11]carbon monoxide and molybdenum(IV) oxide. The latter also reduces carbon dioxide to carbon monoxide and helps improve the performance of the converter. [C-11]Carbon monoxide is purified from remaining [C-11]carbon dioxide and collected in a small silica trap from which it is eluted into a reaction mixture for the palladium-mediated synthesis of a C-11-labelled aromatic ketone. Radiochemical yields of up to 81% (decay-corrected) for [C-11]carbon monoxide were obtained. Radiochemical purity and specific radioactivity of both [C-11]carbon monoxide and the C-11-labelled ketone are sufficient for nuclear medical studies with PET. (C) 1997 Elsevier Science Ltd.