HR: 0800h
AN: H11C-0680    [Abstracts]
TI: A Portable Membrane-based Gas Sampler for Gases Dissolved in Groundwater
AU: Alexander, P
EM: pma2107@columbia.edu
AF: Lamont-Doherty Earth Observatory at Columbia University, 61 Route 9W, Palisades, NY 10964,
AU: * Loose, B
EM: brice@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory at Columbia University, 61 Route 9W, Palisades, NY 10964,
AU: Stute, M
EM: martins@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory at Columbia University, 61 Route 9W, Palisades, NY 10964,
AB: The complications that arise while collecting, transporting and storing groundwater for trace gas analysis have prompted a new approach, which uses membrane technology to obtain a gas sample from the water stream, in the field. This portable groundwater sampler uses a microporous hydrophobic membrane to collect a finite volume of gas, which is in solubility equilibrium with a time-invariant stream of water. Samples of the gas volume can be analyzed to determine original water concentrations for virtually any dissolved gas. The sampler does not require the use of compressed inert gas and its power consumption is minimal. During the development stages, N₂, Ar, O₂, CO₂ and SF₆ were sampled and measured using gas chromatography to evaluate the equilibrium condition and confirm the equilibration time, which was initially gauged using a pressure transducer. Equilibration studies were conducted in the laboratory and at Black Rock Forest, a field site near the Lamont Campus of Columbia University. The time required to achieve solubility equilibrium depends on the dissolved gas content and the water flow rate; 100 cc of gas can be collected, from water in equilibrium with the atmosphere, at low flow (ca. 2 L min^-1) in less than 1 hour. The initial results demonstrate that gauge pressure is a good proxy for solubility equilibrium, and that diffusion can fractionate the gas ratios during rapid mass transfer as indicated by rapid pressure changes.
DE: 0490 Trace gases
DE: 1806 Chemistry of fresh water
DE: 1895 Instruments and techniques: monitoring
SC: Hydrology [H]
MN: 2007 Fall Meeting