Separation of argon from environmental samples for Ar-37 and Ar-39 analyses

High purity argon is required for ultra-low background measurements of Ar-37 and Ar-39. Both short separation times and high argon recovery are required. Here we report the development of an argon separation line from gas samples of 10-120 l volume by a chromatographic desorption from Li-LSX at -120 degrees C. Gases desorb in the order Ar < O-2 < Kr < CH4 approximate to N-2 < CO2, in agreement with published heats of adsorption. The optimum temperature of -120 degrees C for Ar separation from atmospheric air is achieved by a combination of cryogenic cooling with liquid nitrogen and counter-heating. So far, similar to 16,500 l of sample gas have been processed on the separation line. The final purity of the argon is >99.99% with a recovery of >94%. The separation process for 80 l atmospheric air requires 3-4.5 h, which allows the purification of 2 samples per working day. (C) 2016 Elsevier B.V. All rights reserved.