Silicone rubber sampler to measure dissolved gases in saturated soils and waters

Dissolved gases in saturated soils and waters are usually monitored by the gas extraction equilibration technique (EET). A novel sampling technique, u sing silicone tubing, was developed and tested with dissolved nitrous oxide (N2O) and carbon dioxide (CO2). The device consists of a silicone cell enc ased in a PVC pipe through which a continuous Row of water was maintained. Dissolved gases diffuse through the silicons membrane into the cell. Air sa mples were withdrawn from the silicone cell headspace, and gas phase concen trations were converted into dissolved N2O and CO2 using Henrys law coeffic ients. Effluent from the PVC pipe was also collected into evacuated bottles , and dissolved gases content was determined using EET. Statistical analysi s showed no significant difference between the two techniques. Regression a nalysis between concentrations of dissolved N2O and CO2 obtained using the new method (Y) and EET (X) yielded the following relationships: Y = 0.961 X (R-2 = 0.996) and Y = 1.01 X (R-2 = 0.756) for N2O and CO2. respectively. Equilibration time between gas and liquid phases across the silicone membra ne varies with gaseous species, membrane thickness, temperature, and the si licone cell dimensions (volume to area ratio). After nearly I year of opera tion, no indication of microbial growth on the membrane was found. These re sults confirm the development of a new, accurate and versatile technique to monitor dissolved gases. (C) 2001 Elsevier Science Ltd. All rights reserve d.