Molecular Sieves in 14CO2 Sampling and Handling

Molecular sieves are a promising way to sample and manipulate gaseous samples for radiocarbon analyses. Molecular sieve material can adsorb CO2 selectively, enabling sampling of CO2 from large air volumes in a small amount of adsorbent. The sieve material can be regenerated via heating and reused without removing the sieve material from its container. This results in ease of use and reduced risks of atmospheric contamination. Because sieve container volume is small and can be filled with synthetic air or nitrogen, it does not introduce underpressure to the system under study. Hence, sieves are suitable for many different experimental setups, from collection of CO2 from small soil chambers to atmospheric CO2 collection. The most common sieve material in use for sampling CO2 is the 13X zeolite. For environmental measurements starting this year, we have studied the properties of 13X zeolites in more detail. For reliable 14CO2 sampling, there are several caveats that should and can be avoided. In this contribution, we discuss these caveats and solutions to optimize the molecular sieve sampling process.