AN ACOUSTIC PLATE MODE SENSOR FOR AQUEOUS MERCURY

Many industrial processes have resulted in mercury contamination of so ils and potentially of the surrounding groundwater, The remediation ef forts for these sites requires a method of long-term verification. Sen sors with lifetimes of months to years of operation without operator i ntervention are required to monitor these sites. One sensor geometry w hich is capable of detecting relevant concentrations of aqueous mercur y while withstanding typical environmental conditions is the acoustic plate mode (APM) microsensor. This piezoelectric sensor protects the e lectronics from the potentially corrosive aqueous fluid environment wh ile providing a significant interaction with the fluid. Gold films are employed to accumulate the mercury via surface amalgamation. The adde d mass is measured as a change in the resonant frequency of the piezoe lectric element. A reference device helps compensate environmental fac tors, such as temperature drift, solution effects (viscosity, density and conductivity changes) and pressure fluctuations. Initial results i ndicate a sensitivity of approximately 10 ng/ml (10 mu g l(-1)) which is approximately five rimes the limit imposed by the safe drinking wat er act (SDWA) in the US. Research is currently underway to lower this detection limit to allow the sensor to meet the requirements of enviro nmental sensing, wastewater monitoring and drinking water testing.