Developing a low-cost method of purifying and storing methane

Leah Mindorff

Geological Survey of Canada - Quebec

We aim to develop a low-cost method to extract low concentrations of methane (CH4) from permafrost samples in order to measure δ13C and δD values and prepare for Δ13CH3D and 12CH2D2 measurements. This method will involve concentrating, purifying, and storing the CH4 present in the samples. As clumped isotopic measurements are anticipated, a challenge will be keeping the CH4 molecules intact. Current purification methods employ costly He cryostats to play with the freezing temperature of CH4 but we hope to develop a more accessible alternative. To date, we have attempted to transfer CH4 from a sample vial/isojar to a separate vial using a vacuum transfer line, while simultaneously isolating CH4 from other gases (N2) using packed trap with different sorbents. We assume that we were able to transfer all, or nearly all, the CH4 from the first to the second vial because there was no significant isotopic fractionation in the δ13C or δD values (the isotopic values before transfer and after transfer were within ±0.5‰ for δ13C and ±5‰ for δD). We were unable however, to isolate CH4 from other gases in the sample. In fact, it appeared as though we were somehow increasing the amount of N2 during the transfer process. This in turn has prevented us from using the measured relative abundance of CH4 to confirm complete transfer. This method is a work in progress and we invite any feedback or suggestions on ways to improve it.