| A heated, flow-through, membrane-based extraction cell has been designed for the extraction of volatile organic compounds (VOCs) from aqueous solutions. A stream of aqueous sample was pumped through a temperature-controlled channel in the extraction cell, where it was in contact with a polydimethylsiloxane membrane. The VOCs in the sample passed through the membrane and into a gas stream. The air sample containing the VOCs was either detected directly, or it was trapped and desorbed onto a gas chromatography column equipped with a mass selective detector (GC-MS). The extraction cell characteristics and optimum operating conditions were studied. Higher extraction cell temperatures and sample flow rates were found to result in larger analyte responses. Increases in air flow rate in the acceptor channel resulted in a decrease in response. Detection limits using GC-MS were at or below 0.08 microg/L for aromatic hydrocarbons, 2.73 microg/L for THMs, and 0.34 microg/L for the odor causing compounds geosmin and 2-methylisoborneol.;Resistances to mass transfer in the extraction cell were studied using theoretical and experimental data. Both the water and membrane phase resistances were predicted to be significant to mass transport. Three extraction cell variables were examined: sample flow rate, air flow rate, and cell temperature. Boundary layer thickness of the water phase was estimated to be 32 microm at water flow rates of 15 mL/min, and < 10 um when water flow rates exceeded 30 mL/min. Experimental data indicated that under the normal operating conditions of a 15 mL/min sample flow rate at 85 °C, both the membrane and water resistances were significant.;The system was used to monitor the City of Syracuse, New York drinking water in the distribution system for the presence of VOCs related to gasoline contamination and disinfection byproducts formed during chlorination during the summers of 2010 and 2011. The water originated from Skaneateles Lake, an oligotrophic lake used for recreational boating. Aromatic hydrocarbon concentrations were found to fluctuate day to day and were largely associated with summer holiday weekends, likely due to increased motorboat traffic. |
