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High-Precision Isotopic Analysis

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Analytical Services > View by Isotope > Carbon

Hydrogen | Nitrogen| Oxygen | Sulfur

test tubesCarbon Isotope Analysis (13C/12C or δ13C)

For the best possible precision, carbon isotopic compositions of gas components are done by conventional off-line methods consisting of chromatographic separation followed by combustion and dual-inlet isotope ratio mass spectrometry. Reproducibility is generally 0.1 per mil or better. These analyses can also be done by compound-specific analysis (GC-C-IRMS) with somewhat less precision (+/-0.3 per mil) and at significantly lower costs. If high precision is not required for your application, this option will also provide slightly shorter turnaround times. δ13C values can be determined for all C1 to C5 hydrocarbons as well as CO2.

Carbon isotope analysis of dissolved inorganic carbon (DIC) from samples is done by gas stripping. For carbon isotope analysis of solids and other liquids, samples are analyzed using an elemental analyzer interfaced with an isotope ratio mass spectrometer. Carbonates are done by acid digestion.

Sample Type Method Recommended
Sample Size*
Hydrocarbon gases1 Offline prep 300 cc
Hydrocarbon gases1 GC-C-IRMS 20 cc
Hydrocarbon gases1 cryo-enrich 50 cc
Carbon dioxide1 Offline prep 100 cc
Carbon dioxide1 GC-IRMS 20 cc
Dissolved inorganic carbon (DIC) Acid digestion 50 ml
Organic solids EA-IRMS 1 g
Organic liquids and oils EA-IRMS 1 ml
Carbonates Acid digestion 500 mg

1Requires GC analysis

Radiocarbon Analysis ( 14C, carbon-14)

Radiocarbon analysis can be carried out on methane or carbon dioxide gas, or dissolved inorganic carbon (DIC) in water samples. 14C is determined by accelerator mass spectrometry (AMS). All sample preparations are done at Isotech and then purified carbon dioxide is submitted to an established radiocarbon dating laboratory for the final AMS analysis.

Recommended Sample Size* 2 cc of methane1

1Requires GC analysis

Radiocarbon (14C) and Tritium(3H) Analysis of Methane

Relatively large samples of methane are reacted with oxygen (combusted) to form CO2 and water. The CO2 is collected cryogenically and then converted to benzene through a series of reactions. The 14C radioactivity of the benzene is measured by liquid scintillation spectrometry. The tritium activity of the water of combustion is also measured by liquid scintillation spectrometry.

Recommended Sample Size* 5 L methane1

1Requires GC analysis

* Sample volume is based on methane concentration. Ie, requires at least 10 liters of sample with 50% methane.



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