A convenient cryogenic trap with liquid nitrogen for the concentration of [11C]CO2

A simple, inexpensive cryogenic trap for the concentration of [11C]CO2 with liquid nitrogen instead of liquid argon was developed. Trapping temperatures slightly higher than the boiling point of liquid nitrogen (−195.8°C) were achieved by utilizing a temperature gradient formed by heat conduction. Trapping efficiency was> 98% and the [11C]CO2 was thus conveniently concentrated in a small volume of carrier gas.