We developed a portable mass spectrometer (miniRUEDI) for on-site quantification of He, Ar, Kr, N2, O2, CO2, CH4, etc. in terrestrial fluids.1,2 The miniRUEDI is widely used in environmental and geological research to study biogeochemical turnover or to assess the origin, mixing and exchange of fluids. The instrument is designed for on-site gas analysis during field work at remote locations and allows quantification of individual gas species in gaseous or aqueous matrices. The partial pressures of the gas species in a gas sample are calibrated by peak-height comparison relative to a reference gas with well known partial pressures. In many cases, ambient air can be used as a convenient reference gas.
For quantification of dissolved gases in water, we developed the gas-eqilibrium membrane-inlet mass spectrometry (GE-MIMS) technique.1,3 The GE-MIMS technique uses an equilibrator module that contains a gas-permeable membrane to separate a small gas headspace from the water that is purged through the module. The gases dissolved in the water equilibrate with the gas headspace according to Henrys Law, and their partial pressures are quantified using the miniRUEDI. The aqueous concentrations of the gas specis are determined from the partial pressures by inverting Henry Law. The miniRUEDI+GE-MIMS analysis operates autonomously and yields accurate and precise concentrations of dissolved gases with a time resolution of approximately 10 minutes.
Such high-resolution time series and the immediate availability of the data open up new opportunities for research in highly dynamic and heterogeneous environmental systems. The combined analysis of inert and reactive gas species provides direct information on the linkages of physical and biogoechemical processes in aquatic systems, such as the air/water gas exchange, excess air formation, inflow of geogenic fluids, O2 turnover, N2 production by denitrification, or the production and dynamics of greenhouse gases (CH4, CO2). This presentation will highlight different application examples where the miniRUEDI+GE-MIMS system was used (I) to study the response of the flow dynamics and water quality in an aquifer linked to a revitalized river, (II) to identify the outflow of deep, saline groundwater and its effects on the water quality in a large drainage basin, and (III) to disentangle and quantify biogeochemical turnover vs. physical gas dynamics in a riparian zone.
References:
[1] Brennwald, M.S., Schmidt, M., Oser, J., and Kipfer, R. (2016). Environmental Science and Technology, 50(24):13455–13463, doi: 10.1021/acs.est.6b03669
[2] Gasometrix GmbH, gasometrix.com
[3] Patent EP4109092