One common problem in the field of organic isotope geochemistry is the long-term storage of small aliquots of CO2 that are extracted from samples. This challenge arises primarily because high-precision, high-accuracy measurements of small samples often require laborious methods. The CO2 must be extracted carefully to minimize contamination, transferred from the extraction apparatus to the storage apparatus without losses, and the whole process must proceed without isotopic fractionation. For these reasons, such methods have a limited throughput that cannot accumulate enough samples in a reasonable timescale for efficient use of an isotope ratio mass spectrometer (IRMS). Therefore, we devised a simple protocol for storing small aliquots of CO2 in capillary tubes, allowing the analyst to accumulate batches of samples over time. The capillaries are easily cracked inside helium-filled Exetainer vials, which are then loaded into a gas bench for automated IRMS analysis. It’s easy, accurate, and reliable.
In our quest to develop the method, we initially loaded Exetainers with handblown glass marbles in order to increase the likelihood of cracking the capillaries via shaking. This worked, but created additional challenges that led to lost samples, such as seizing and occasional breakage of the Exetainer. These challenges were partially alleviated by twisting “nurdles” into the capillaries prior to use. Ultimately, slow-motion videos revealed that gently smacking the Exetainer against an open palm imparted enough energy to crack the capillary without the marbles or nurdles. This simplification makes the method much easier to use and it greatly reduces the number of lost samples per batch.
For a full description of the method, including videos of some righteous tube crackin’, please check out our latest publication in Rapid Communications in Mass Spectrometry:
Walker, B. D., S. R. Beaupre, S. Griffin, J. Walker, E. Druffel, and X. Xu (2020), A sealed‐tube method for offline δ13C analysis of CO2 via a Gas Bench II continuous flow isotope ratio mass spectrometer, Rapid Commun Mass Spectrom, doi:10.1002/rcm.9040.