GC-IRMS
Definition
Gas chromatography isotope ratio mass spectrometry: compounds separated by GC are combusted (for 13C) or pyrolysed (for 2H) and the isotope ratio of the resulting CO2 or H2 is measured by a magnetic-sector IRMS. Provides compound-specific delta-13C and delta-2H values that are geologically determined and immutable under weathering.
- Full name
- Gas chromatography isotope ratio mass spectrometry
- Measures
- Compound-specific delta-13C and delta-2H values
- Sample treatment
- Combustion (13C) or pyrolysis (2H) after GC separation
- Key property
- Isotope ratios are geologically set and immutable under weathering
Common questions
Why does isotope immutability under weathering matter for petroleum comparisons?+
Evaporation and biodegradation change a spilled or burned petroleum product's bulk composition and volatile profile substantially, but they do not measurably alter the isotope ratios locked into individual compounds, so GC-IRMS values remain comparable between a weathered sample and its unweathered source long after conventional GC-MS matching has become unreliable.
How does GC-IRMS differ from standard GC-MS compound identification?+
GC-MS identifies compounds by their fragmentation pattern, while GC-IRMS goes a step further to measure the isotopic composition of carbon or hydrogen within each separated compound, providing a source-linked signature rather than just a structural identification.
What kind of case relies on GC-IRMS specifically rather than bulk isotope analysis?+
Cases needing to link a specific petroleum product, such as fuel from a fire scene, to a particular source or batch use compound-specific GC-IRMS because bulk sample isotope analysis averages across all constituents and can mask distinctions that individual compounds still preserve.
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