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, using silicone tubing, was developed and tested with dissolved nitrous oxide (N2O) and carbon dioxide (CO2). The device consists of a silicone cell encased in a PVC pipe through which a continuous flow of water was maintained. Dissolved gases diffuse through the silicone membrane into the cell. Air samples were withdrawn from the silicone cell headspace, and gas phase concentrations were converted into dissolved N2O and CO2 using Henryʹs law coefficients. Effluent from the PVC pipe was also collected into evacuated bottles, and dissolved gases content was determined using EET. Statistical analysis showed no significant difference between the two techniques. Regression analysis between concentrations of dissolved N2O and CO2 obtained using the new method (Y) and EET (X) yielded the following relationships: Y=0.961 X (R2=0.996) and Y=1.01 X (R2=0.756) for N2O and CO2, respectively. Equilibration time between gas and liquid phases across the silicone membrane varies with gaseous species, membrane thickness, temperature, and the silicone cell dimensions (volume to area ratio). After nearly 1 year of operation, no indication of microbial growth on the membrane was found. These results confirm the development of a new, accurate and versatile technique to monitor dissolved gases.