Field continuous measurement of dissolved gases with a CF-MIMS: Applications to the physics and biogeochemistry of groundwater flow

International audienceIn the perspective of a temporal and spatial exploration of aquatic environments (surface and groundwater), we developed a technique for field continuous measurements of dissolved gases with a precisionbetter than 1% for N2, O2, CO2, He, Ar, 2% for Kr, 8% for Xe, and 3% for CH4, N2O and Ne. With a largeresolution (from 1×10-9 to 1×10-2 5 ccSTP/g) and a capability of high frequency analysis (1 measure every 2seconds), the CF-MIMS (Continuous Flow Membrane Inlet Mass Spectrometer) is an innovative toolallowing the investigation of a large panel of hydrological and biogeochemical 7 processes in aquaticsystems. Based on the available MIMS technology, this study introduces the development of the CF-MIMS(conception for field experiments, membrane choices, ionisation) and an original calibration procedureallowing the quantification of mass spectral overlaps and temperature effects on membrane permeability.This study also presents two field applications of the CF-MIMS involving the well-logging of dissolvedgases and the implementation of groundwater tracer tests with dissolved 413 He. The results demonstrate theanalytical capabilities of the CF-MIMS in the field. Therefore, the CF-MIMS is a valuable tool for thefield characterisation of biogeochemical reactivity, aquifer transport properties, groundwater recharge,groundwater residence time and aquifer-river exchanges from few hours to several weeks experiments