ELECTROCHEMICAL PIEZOELECTRIC SENSORS FOR TRACE IONIC CONTAMINANTS

Industrial processes, such as fossil fuel combustion and nuclear mater ials processing, have resulted in heavy metal contamination of soils a nd potentially of the surrounding groundwater. In particular, mercury contamination of groundwater is a serious threat to the ecosystem, cum ulating in serious health problems for humans as well as wildlife. Mon itoring of mercury contamination in groundwater requires a method of l ong-term verification. Sensors with lifetimes of months to years of op eration without operator intervention are required. One sensor geometr y, which is capable of detecting relevant concentrations of aqueous io nic contaminants, such as mercury, while withstanding typical environm ental conditions, is the shear horizontal acoustic plate mode (SHAPM) sensor. This sensor protects the electronics from the potentially corr osive aqueous fluid environment while providing a significant interact ion with the fluid. Gold films are employed to accumulate the mercury via surface amalgamation. The added mass is measured as a change in th e resonant frequency of the piezoelectric sensing element. Electrochem ical techniques are employed to impart reversibility and to accelerate response kinetics. Results indicate a sensitivity of approximately 2. 4 ng/mL, which approaches the 2.0 ng/mL limit imposed by the Safe Drin king Water Act (SDWA).