Abstract: Environmental monitoring of low concentration of organic compounds in a medium such as ground water or another environmental fluid is effected by using a diffusion cell (112) having a polymeric membrane formed into a helical tube (125) and immersed in the environmental fluid so that organic compounds at ppb and ppt concentrations diffuse into and through the polymeric material. A carrier gas in the polymeric tube acquires a concentration of the organic compounds substantially in equilibrium with the concentration of the organic compounds in the environmental fluid. For the purpose of permitting monitoring with detectors (116) which are not sensitive to extremely low levels of organic compounds, a concentrating device such as a thermal desorption tube (114) can be provided for processing the gas and periodic thermal activation to discharge therefrom organic compounds to be detected at a sensor.

Abstract: A Diffusion cell for use in monitoring levels of gases or volatile organic compounds within bulk media such as ground water, effluent, or air. The diffusion cell is of sealed hollow construction and has a membrane providing an interface between a gas phase contained within the diffusion cell and the bulk media. The membrane is permeable to gas and volatile organic compounds while being relatively impermeable to water (i.e. hydrophobic). The diffusion cell includes a core of porous material to minimize the internal volume within. In use, a sensor is located in close proximity to the core of porous material to minimize the dead volume between the sensor and the diffusion cell. The minimization of the internal and dead volumes allows for decreased response times to fluctuations in levels being measured, lending the diffusion cell to real time monitoring applications.