[11 C]Carfentanil ([11 C]CFN) is a selective radiotracer for in vivo positron emission tomography imaging studies of the μ-opioid system that, in our laboratories, is synthesized by methylation of the corresponding carboxylate precursor with [11 C]MeOTf, and purified using a C2 solid-phase extraction cartridge. Changes in the commercial availability of common C2 cartridges have necessitated future proofing the synthesis of [11 C]CFN to maintain reliable delivery of the radiotracer for clinical imaging studies. An updated synthesis of [11 C]CFN is reported that replaces a now obsolete purification cartridge with a new commercially available version and also substitutes the organic solvents used in traditional production methods with ethanol
