The bubble stripping method for determining dissolved hydrogen (H2) in well water

Abstract

The bubble stripping method was developed for use at field sites to measure the concentration of dissolved hydrogen (H2) in ground water. This information is useful in assessing the viability of employing monitored natural attenuation (MNA) as a strategy to influence the restoration of sites contaminated with chlorinated solvents. In laboratory studies, a reservoir containing water was employed to simulate a well. The system was constructed so that the concentration of dissolved H2 could be maintained at a constant level. The method was applied by pumping water from the reservoir into a sample cell, and then injecting 20 ml of nitrogen into the cell to produce a headspace (the “bubble”). Stripping was accomplished by pumping water through the cell, which produced agitation between the aqueous phase and the headspace. Pumping was continued for a length of time sufficient for dissolved H2 to partition between the two phases. Analysis of H2 in the headspace by gas chromatography enabled the concentration of dissolved H2 in solution to be calculated with the use of Henry's law. Two sample cell designs were compared in this study, the Microseeps Cell and the Chapelle Cell. Kinetics of equilibration studies were conducted with each cell, employing solution flow rates of 200, 300, and 400 ml/min, at 4 and 21 °C. The Microseeps Cell compared favorably with the Chapelle Cell with regards to kinetics of equilibration, with the added benefit of costing significantly less. © 2000 John Wiley & Sons, Inc. Field Analyt Chem Technol 4: 283–296, 2000