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Updated: Mar 12, 2026

Measuring Dissolved Methane in Aquatic Ecosystems Using An Optical Spectroscopy Gas Analyzer
Published on: July 26, 2024
Analysis of hydrogen and methane in seawater by "Headspace" method: Determination at trace level with an automatic
1Unité des Géosciences Marines Géosciences Marines, Laboratoire Cycles Géochimiques et ressources IFREMER Centre de Brest, Plouzané, France.
Abstract:
"Headspace" technique is one of the methods for the onboard measurement of hydrogen (H2) and methane (CH4) in deep seawater. Based on the principle of an automatic headspace commercial sampler, a specific device has been developed to automatically inject gas samples from 300ml syringes (gas phase in equilibrium with seawater). As valves, micro pump, oven and detector are independent, a gas chromatograph is not necessary allowing a reduction of the weight and dimensions of the analytical system. The different steps from seawater sampling to gas injection are described. Accuracy of the method is checked by a comparison with the "purge and trap" technique. The detection limit is estimated to 0.3nM for hydrogen and 0.1nM for methane which is close to the background value in deep seawater. It is also shown that this system can be used to analyze other gases such as Nitrogen (N2), carbon monoxide (CO), carbon dioxide (CO2) and light hydrocarbons.
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