Field evaluation of acoustic-wave chemical sensors for monitoring of organic solvents in groundwater

An instrument for in-situ monitoring of volatile organics in groundwater at pat-per-billion levels has been developed and field tested. The device is an acoustic wave thickness-shear mode sensor based on a 10-MHa AT-cut quartz resonator coated with a non-polar polymer film. The sensor demonstrates a detection limit of 8 and 12 parts per billion in water for trichloroethylene and toluene, respectively, and a rapid reversible response. This low detection limit is achieved by carefully minimizing the noise level in the electronic detection system, by optimizing the thickness of the sensing polymer film, and by performing measurements in the headspace. Preliminary field test demonstrated good correlation of sensor response with conventional laboratory purge-and-trap/GC analysis.