Dept. of Environmental Science and Engineering
Oregon Graduate Center
In this study aqueous adsorption/thermal desorption (ATD) with the porous polymer sorbent Tenax has been investigated as a sampling and analysis methodology for the determination of sub-Âµg/L levels of volatile organic compounds (VOC) in groundwater. During the sampling step, water is passed through a glass cartridge containing Tenax and organic compounds are concentrated by the sorbent (adsorption). During the analysis step, the cartridge is heated while an inert gas is passed through the sorbent (thermal desorption). This step recovers trapped compounds and transfers them to a gas chromatograph-mass spectrometer where they are separated and analyzed. Relative to other sampling and analysis procedures frequently used, ATD minimizes sample handling, allows an investigator to obtain samples from small diameter groundwater monitoring wells, and offers increased method sensitivity. Four aspects concerning the use of ATD have been studied. First, a new ATD cartridge analysis technique was developed and tested. Second, a field evaluation of ATD was performed. In this portion of the study ATD was compared with a traditional sampling and analysis technique at three sampling sites at which groundwater was known to be contaminated with a variety of VOCs. For the third portion of the study, laboratory experiments were conducted to determine the capacity of the sorption system as a function of sample matrix and individual compound concentration. In addition, these experiments were used to estimate the method sensitivity of ATD for a group of VOCs with a range of physical properties. The final aspect of this thesis involved the determination of the ability of two models to accurately predict the adsorption efficiency of this sampling system under a variety of sampling conditions. Model parameters determined from laboratory experiments were used with each model, and model predictions were directly compared with experimental results in order to determine the accuracy of each model. ATD was determined to be sensitive, accurate relative to more commonly used techniques, and precise. In addition, experimental information now exists for a group of VOCs which will allow a priori predictions concerning adsorption efficiency to be made for similar compounds under a variety of sampling conditions.
Rosen, Michael Elliott, "The development of adsorption/thermal desorption for the determination of trace levels of volatile organic compounds in groundwater" (1988). Scholar Archive. 254.