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

A new method for the efficient conversion of no-carrier-added [11C]carbon dioxide into [11C]carbon monoxide is described. [11C]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°C. [11C]Carbon dioxide readily reacts with molybdenum to form [11C]carbon monoxide and molybdenum(IV) oxide. The latter also reduces carbon dioxide to carbon monoxide and helps improve the performance of the converter. [11C]Carbon monoxide is purified from remaining [11C]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 11C-labelled aromatic ketone. Radiochemical yields of up to 81% (decay-corrected) for [11C]carbon monoxide were obtained. Radiochemical purity and specific radioactivity of both [11C]carbon monoxide and the 11C-labelled ketone are sufficient for nuclear medical studies with PET.