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In-Line Combustion System for the Measurement of δ13C-CH4 in Gas Reference Materials Using Optical Isotope Ratio Spectroscopy

Hillier, Aimee ; Mussell-Webber, Eric ; Hopkinson, Emily ; Wilson, Freya ; Nehrbass-Ahles, Christoph ; Brewer, Paul J. ; Worton, David R. ; Rennick, Christopher ; Arnold, Tim LU orcid and Moossen, Heiko , et al. (2025) In Analytical Chemistry 97(24). p.12513-12520
Abstract

Measurements of the stable carbon isotope ratio in methane (δ13C-CH4) are used in determining the source of CH4 emissions on local, regional, and global scales. To achieve the required level of data comparability for atmospheric monitoring networks, accurate gas reference materials of δ13C-CH4 in air are required with high levels of reproducibility. We describe a method to determine the δ13C-CH4 of CH4 in synthetic air reference materials reported against the Vienna Pee Dee Belemnite (VPDB) scale. The measurement principle converts CH4 into carbon dioxide (CO2) via direct combustion using a platinum catalyst. Subsequently, the... (More)

Measurements of the stable carbon isotope ratio in methane (δ13C-CH4) are used in determining the source of CH4 emissions on local, regional, and global scales. To achieve the required level of data comparability for atmospheric monitoring networks, accurate gas reference materials of δ13C-CH4 in air are required with high levels of reproducibility. We describe a method to determine the δ13C-CH4 of CH4 in synthetic air reference materials reported against the Vienna Pee Dee Belemnite (VPDB) scale. The measurement principle converts CH4 into carbon dioxide (CO2) via direct combustion using a platinum catalyst. Subsequently, the CO2 resulting from CH4 combustion was analyzed for δ13C-CO2 using OIRS (optical isotope ratio spectroscopy) against CO2 in synthetic air reference materials traceable to the δ13CVPDB scale. The δ13C-CH4 of four nominally 410 μmol mol-1 CH4 in synthetic air reference materials, prepared in pairs from two CH4 sources with distinct δ13C-CH4 were certified with an average δ13C-CH4 of −39.07‰ and −51.91‰. Measurement reproducibility within 0.17‰ was demonstrated between measurements of the two reference materials from each CH4 source. Agreement to traceable measurements of the pure CH4 was achieved within reported measurement reproducibility. Combined expanded uncertainties (k= 2) between 0.4 and 1.5‰ have been demonstrated. The sensitives of the conversion system to flow rate have been assessed and found to have a negligible impact on the certification of δ13C-CH4. Thus, we demonstrate that a combustion system coupled to OIRS measurement of CO2 can provide a means of useful measurement of δ13C-CH4 traceable to VPDB.

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organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Analytical Chemistry
volume
97
issue
24
pages
8 pages
publisher
The American Chemical Society (ACS)
external identifiers
  • pmid:40488659
  • scopus:105007817566
ISSN
0003-2700
DOI
10.1021/acs.analchem.4c06540
language
English
LU publication?
yes
additional info
Publisher Copyright: © 2025 The Authors. Published by American Chemical Society.
id
aee57900-db32-4f2d-bf8c-d3e7ce6ac61d
date added to LUP
2025-09-19 15:08:46
date last changed
2025-10-17 18:59:37
@article{aee57900-db32-4f2d-bf8c-d3e7ce6ac61d,
  abstract     = {{<p>Measurements of the stable carbon isotope ratio in methane (δ<sup>13</sup>C-CH<sub>4</sub>) are used in determining the source of CH<sub>4</sub> emissions on local, regional, and global scales. To achieve the required level of data comparability for atmospheric monitoring networks, accurate gas reference materials of δ<sup>13</sup>C-CH<sub>4</sub> in air are required with high levels of reproducibility. We describe a method to determine the δ<sup>13</sup>C-CH<sub>4</sub> of CH<sub>4</sub> in synthetic air reference materials reported against the Vienna Pee Dee Belemnite (VPDB) scale. The measurement principle converts CH<sub>4</sub> into carbon dioxide (CO<sub>2</sub>) via direct combustion using a platinum catalyst. Subsequently, the CO<sub>2</sub> resulting from CH<sub>4</sub> combustion was analyzed for δ<sup>13</sup>C-CO<sub>2</sub> using OIRS (optical isotope ratio spectroscopy) against CO<sub>2</sub> in synthetic air reference materials traceable to the δ<sup>13</sup>C<sub>VPDB</sub> scale. The δ<sup>13</sup>C-CH<sub>4</sub> of four nominally 410 μmol mol<sup>-1</sup> CH<sub>4</sub> in synthetic air reference materials, prepared in pairs from two CH<sub>4</sub> sources with distinct δ<sup>13</sup>C-CH<sub>4</sub> were certified with an average δ<sup>13</sup>C-CH<sub>4</sub> of −39.07‰ and −51.91‰. Measurement reproducibility within 0.17‰ was demonstrated between measurements of the two reference materials from each CH<sub>4</sub> source. Agreement to traceable measurements of the pure CH<sub>4</sub> was achieved within reported measurement reproducibility. Combined expanded uncertainties (k= 2) between 0.4 and 1.5‰ have been demonstrated. The sensitives of the conversion system to flow rate have been assessed and found to have a negligible impact on the certification of δ<sup>13</sup>C-CH<sub>4</sub>. Thus, we demonstrate that a combustion system coupled to OIRS measurement of CO<sub>2</sub> can provide a means of useful measurement of δ<sup>13</sup>C-CH<sub>4</sub> traceable to VPDB.</p>}},
  author       = {{Hillier, Aimee and Mussell-Webber, Eric and Hopkinson, Emily and Wilson, Freya and Nehrbass-Ahles, Christoph and Brewer, Paul J. and Worton, David R. and Rennick, Christopher and Arnold, Tim and Moossen, Heiko and Rothe, Michael and Geilmann, Heike and Dylag, Caroline and Hill-Pearce, Ruth E.}},
  issn         = {{0003-2700}},
  language     = {{eng}},
  month        = {{06}},
  number       = {{24}},
  pages        = {{12513--12520}},
  publisher    = {{The American Chemical Society (ACS)}},
  series       = {{Analytical Chemistry}},
  title        = {{In-Line Combustion System for the Measurement of δ<sup>13</sup>C-CH<sub>4</sub> in Gas Reference Materials Using Optical Isotope Ratio Spectroscopy}},
  url          = {{http://dx.doi.org/10.1021/acs.analchem.4c06540}},
  doi          = {{10.1021/acs.analchem.4c06540}},
  volume       = {{97}},
  year         = {{2025}},
}