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A new automated method for high‐throughput carbon and hydrogen isotope analysis of gaseous and dissolved methane at atmospheric concentrations
Author(s) -
Smith Andrew C.,
Welsh Steve,
Atkinson Helen,
Harris David,
Leng Melanie J.
Publication year - 2021
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.9086
Subject(s) - chemistry , methane , isotope ratio mass spectrometry , isotope analysis , isotopes of carbon , environmental chemistry , carbon fibers , gas chromatography , analytical chemistry (journal) , chromatography , total organic carbon , organic chemistry , ecology , materials science , composite number , composite material , biology
Rationale The dual isotope ratio analysis, carbon (δ 13 C value) and hydrogen (δ 2 H value), of methane (CH 4 ) is a valuable tracer tool within a range of areas of scientific investigation, not least wetland ecology, microbiology, CH 4 source identification and the tracing of geological leakages of thermogenic CH 4 in groundwater. Traditional methods of collecting, purification, separating and analysing CH 4 for δ 13 C and δ 2 H determination are, however, very time consuming, involving offline manual extractions. Methods Here we describe a new gas chromatography, pyrolysis/combustion, isotope ratio mass spectrometry (IRMS) system for the automated analysis of either dissolved or gaseous CH 4 down to ambient atmospheric concentrations (2.0 ppm). Sample introduction is via a traditional XYZ autosampler, allowing either helium (He) purging of gas or sparging of water from a range of suitable, airtight bottles. Results The system routinely achieves precision of <0.3‰ for δ 13 C values and <3.0‰ for δ 2 H values, based on long‐term replicate analysis of an in‐house CH 4 /He mix standard (BGS‐1), corrected to two externally calibrated reference gases at near atmospheric concentrations of methane. Depending upon CH 4 concentration and therefore bottle size, the system runs between 21 (140‐mL bottle) and 200 samples (12‐mL exetainer) in an unattended run overnight. Conclusions This represents the first commercially available IRMS system for dual δ 13 C and δ 2 H analysis of methane at atmospheric concentrations and a step forward for the routine (and high‐volume) analysis of CH 4 in environmental studies.