Anaerobic oxidation of methane

The samples are incubated anaerobically with 14CH4-tracer, which is transformed into 14CO2. Depending on the expected rate, the incubation time varies between 8 and 24 hours.

The ongoing AOM process with the tracer is stopped by transferring the sample to 50 ml glass jars containing 25 ml NaOH (2,5 %) => separation of CO2 (dissolved in NaOH) and CH4 (remains in headspace and is measured first)

a)

[12+14CH4] is measured with ion gas-chromatography:

From the resulting area of the GC measurement the methane concentration is calculated:

b)

Headspace (i.e. complete methane) is burned and 14CH4 measured indirectly through amount of 14CO2 after burning:

The sample headspace is connected to the oven where it is burned and the 14CO2 trapped in two succeeding 20 ml scyntillation vials containing 1 ml phenylethylamine + 7 ml ethylenglycolmonomethylether

Both vials are measured in the scintillation counter after the addition of 10 ml Ultima-Gold. The two values are added and the amount of 14CO2 calculated from the activity.

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