[11C] Methylation on a C18 Sep-Pak cartridge: A convenient way to produce [N-methyl-11C] choline

[N-Methyl-¹¹C]choline has been simply and efficiently labelled at room temperature by solid supported [¹¹C]methylation of 2-dimethylaminoethanol on a commercial C₁₈ Sep-Pak Light cartridge. The labelled product was retained on a cation exchange resin (Sep-Pak Plus Accell Plus CM) and washed with ethanol and water to remove any excess precursor. Then [N-methyl-¹¹C]choline was desorbed from the cartridge by elution with saline, passed through a 0.2 mm sterile filter and collected in a sterile vial. Overall, the total synthesis time was 12 min from the end of bombardment (EOB). The radiochemical yield from [¹¹C]CO₂, decay corrected (EOB) was 87 and the radiochemical purity was greater than 99. Very conveniently, the automated apparatus employed is a very simple modification of the system routinely used for the synthesis of L-[S-methyl-¹¹C]methionine.