09 Oct 2023
 | 09 Oct 2023
Status: this preprint is open for discussion and under review for Atmospheric Measurement Techniques (AMT).

Extraction, purification, and clumped isotope analysis of methane (Δ13CDH3 and Δ12CD2H2) from sources and the atmosphere

Malavika Sivan, Thomas Röckmann, Carina van der Veen, and Maria Elena Popa

Abstract. Measurements of the clumped isotope anomalies (Δ13CDH3 and Δ12CD2H2) of methane (CH4) have shown potential for constraining CH4 sources and sinks. Together with the bulk isotopic composition, they can be used to unravel the information about the formation and history of CH4. At Utrecht University, we use the Thermo Ultra high-resolution isotope ratio mass spectrometer to measure the clumped isotopic composition of CH4 from samples of various origins such as geologic sites, biogenic systems, and laboratory incubation experiments, and from the atmosphere.

We have developed an extraction system with three sections for extracting and purifying CH4 from high (>1 %), medium (0.1–1 %), and low-concentration (< 1 %) samples, including atmospheric air (~2 ppm = 0.0002 %). Depending on the CH4 concentration, a quantity of sample gas is processed that delivers 3 ± 1 mL of pure CH4, which is the quantity typically needed for one clumped isotope measurement. For atmospheric air with a CH4 mole fraction of 2 ppm, we currently process up to 1100 L of air.

The analysis is performed on pure CH4, using a dual inlet setup. The complete measurement time for all isotope signatures is about 20 hours for one sample. The mean internal precision of sample measurements is 0.3 ± 0.1 ‰ for Δ13CDH3 and 2.4 ± 0.8 ‰ for Δ12CD2H2. The long-term reproducibility, obtained from repeated measurements of a constant target gas, over almost 3 years, is around 0.15 ‰ for Δ13CDH3 and 1.2 ‰ for Δ12CD2H2. The measured clumping anomalies are calibrated via the Δ13CDH3 and Δ12CD2H2 values of the reference CH4 used for the dual inlet measurements. These were determined through isotope equilibration experiments at temperatures between 50 and 450 °C.

Here, we describe in detail the optimized sampling, extraction, purification, and measurement technique followed in our laboratory to measure the clumping anomalies of CH4 precisely and accurately. We also give an overview of the results of samples of various origins measured using this procedure.

Malavika Sivan et al.

Status: open (until 29 Dec 2023)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse

Malavika Sivan et al.


Total article views: 294 (including HTML, PDF, and XML)
HTML PDF XML Total Supplement BibTeX EndNote
190 96 8 294 17 5 9
  • HTML: 190
  • PDF: 96
  • XML: 8
  • Total: 294
  • Supplement: 17
  • BibTeX: 5
  • EndNote: 9
Views and downloads (calculated since 09 Oct 2023)
Cumulative views and downloads (calculated since 09 Oct 2023)

Viewed (geographical distribution)

Total article views: 320 (including HTML, PDF, and XML) Thereof 320 with geography defined and 0 with unknown origin.
Country # Views %
  • 1
Latest update: 08 Dec 2023
Short summary
We have set up a measurement system for methane clumped isotopologues. We have built an extraction and purification system to extract pure methane for these measurements, for samples of various origins, including atmospheric air, for which we need to process about 1000 L of air for one measurement. We report here the technical setup for extraction and measurements, the calibration, and give an overview of the samples measured so far.