In Situ Monitoring of Vapor Phase TCE Using a Chemiresistor Microchemical Sensor |
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| Authors: | Clifford K Ho Charles F Lohrstorfer |
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| Institution: | Clifford K. Ho;is a Distinguished Member of the technical staff at Sandia National Laboratories (P.O. Box 5800, Albuquerque, NM 87185;(505) 844–2384;fax (505) 844–7354;). He received a B.S. in mechanical engineering from the University of Wisconsin-Madison (1989), and an M.S. and Ph.D. in mechanical engineering from the University of California at Berkeley (1990, 1993), Dr. Ho has more than 10 years of experience in experimental and numerical studies involving multiphase heat- and mass-transfer processes in porous media. He is currently leading a research project to develop microchemical sensors for continuous, in situ, subsurface monitoring of volatile organic compounds (see ). Charles F. Lohrstorfer;is the Bechtel Nevada principal investigator for Advanced Monitoring Systems Initiative (Bechtel Nevada Corp., P.O. Box 98521, MIS NLV082;Las Vegas, NV 89193). He is a systems engineer with a B.S. and M.S. in engineering with more than 20 years of science and engineering experience. Prior to joining Bechtel Nevada, he worked on several projects related to sensor systems that included developing sensor systems for field studies of hydrologic properties at the University of Arizona, serving as surface analyst in the development laboratory for thin film media at IBM, and performing R&D of systems to detect evidence of weapons of mass destruction at the U.S. Air Force, McClellan Central Laboratory. |
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| Abstract: | A chemiresistor microchemical sensor has been developed to detect and monitor volatile organic compounds in unsaturated and saturated subsurface environments. A controlled study was conducted at the HAZMAT Spill Center at the Nevada Test Site, where the sensor was tested under a range of temperature, moisture, and trichloroethylene (TCE) concentrations. The sensor responded rapidly when exposed to TCE placed in sand, and it also responded to decreases in TCE vapor concentration when clean air was vented through the system. Variations in temperature and water vapor concentration impacted baseline chemiresistor signals, but at high TCE concentrations the sensor response was dominated by the TCE exposure. Test results showed that the detection limit of the chemiresistor to TCE vapor in the presence of fluctuating environmental variables (i.e., temperature and water vapor concentration) was on the order of 1000 parts per million by volume, which is about an order of magnitude higher than values obtained in controlled laboratory environments. Automated temperature control and preconcentration is recommended to improve the stability and sensitivity of the chemiresistor sensor. |
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