Abstract
Dissolved gases are particularly relevant tools for the investigation of environmental processes. Indeed, their solubility being a function of the variables of physical state of the medium (temperature, pressure, salinity), the dissolved noble gases are for instance good indicators of equilibrium conditions with the atmosphere and mixing of water bodies. Dissolved gases can also inform the biogeochemical functioning of natural systems by providing information on major processes such as photosynthesis, respiration or denitrification. Classical methods relying on the sampling, the storage and the ex situ analysis of water samples for the measurement of dissolved gases suffer from the difficulty of taking sufficiently frequent and representative samples as well as the analyte preservation. High-frequency in situ measurement of dissolved gases is therefore the most relevant for the study of environmental processes. The use of Membrane Inlet Mass Spectrometer (MIMS) technology provides access to high frequency measurements of a large set of dissolved gases in the field (He, Ne, Ar, Kr, Xe, N2, O2, CO2, CH4, N2O, H2) which offers a real opportunity for environmental studies.
Highlights
Dissolved gas measurements are valuable tools for the investigation of physical, geochemical and biological processes taking place in aquatic environments
The originality of the CF-Membrane Inlet Mass Spectrometer (MIMS) lies in the introduction of the analytes directly into the vacuum of the mass spectrometer (P < 5×10-6 Torr) using a semi-permeable membrane which extracts a fraction of the dissolved gases from flowing liquids
The CF-MIMS consists in a promising tool allowing the high-frequency measurement of several dissolved gases (He, Ne, Ar, Kr, Xe, N2, CO2, O2, CH4, N2O and H2) in the field
Summary
Dissolved gas measurements are valuable tools for the investigation of physical, geochemical and biological processes taking place in aquatic environments. Field dissolved gases measurements consist in a promising alternative to classical methods relying on sampling and ex situ analyses In this respect, dissolved gas specific sensors (O2, CO2 and CH4) have been widely developed for environmental studies as they provided both the opportunity to overcome the issues related to sampling and the possibility to perform long-term high-frequency monitoring. We detail a new approach for the field continuous measurement of dissolved gases in aquatic environments with a CF-MIMS (Continuous Flow Membrane Inlet Mass Spectrometer). This technique allows the in situ high-frequency monitoring of dissolved noble and reactive gases (He, Ne, Ar, Kr, Xe, N2, CO2, O2, CH4, N2O and H2) directly on water flows. After presenting the details of the analytical method and the calibration procedure, the field capabilities of the CF-MIMS are illustrated at the Orgeval Critical Zone Observatory through the in situ monitoring of the diurnal biogeochemical dynamics of the Avenelles River
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