Performances of a TRACERlab FX C synthesis module using a Ni-nanopowder/molecular sieves mixed catalyst

Abstract

The progress of positron emission tomography goes together with an increasing demand for new radiopharmaceuticals: among these, the development of radiopharmaceuticals labelled with carbon-11 is particularly interesting because these compounds are biologically indistinguishable from their stable analogues. These radiotracers are prepared starting from [11C]carbon dioxide, the most common and versatile primary labelling precursor, or from secondary labelling precursors such [11C]methyl iodide produced by “wet” or “gas-phase” method. The gas-phase is the most used method and consists in the radical reaction of iodine vapours with [11C]methane, produced in target or from [11C]carbon dioxide by reduction with hydrogen on nickel catalyst at high temperature. This second approach is frequently adopted in commercial automatic methylation modules, such as the TRACERlab FX C. When not performed in target, [11C]CH4 production represents a key step for the [11C]CH3I synthesis from which the outcome of the whole radiolabelling process depends. In order to improve the performance of the module, a new reduction catalyst made of a mixture of metallic Ni (nanopowder) and molecular sieves mixed in different ratios has been tested. Preliminary results demonstrated that not only the mixture of nanopowder-Ni and molecular sieves represents a valid reduction catalyst but also permits to trap [11C]CO2 and subsequently use it as labelling reagent, making TRACERlab FX C a module for both methylation and carboxylation.