Preliminary Study of a Prototype Methyl - Mercury Monitor for In - Field Pore Water Sample Analyses – 11559

This study involves proof-of-concept research for an innovative, low-cost, and portable methylmercury (MeHg) monitor to be utilized at Oak Ridge Reservation (ORR) creek beds. The MeHg monitor comprises three primary steps: (1) chemical derivatization; (2) preconcentration using the purge-and-trap (P&T) method; and (3) sensing using Quartz Crystal Microbalance (QCM) sensors. This preliminary study deals with the measurement of only inorganic mercury (Hg) (e.g. Hg) which was measured using a modified version of the U.S. Environmental Protection Agency’s (U.S. EPA) Method 1631, Revision E for chemical reduction using stannous chloride (SnCl2). Preconcentration was handled using a gold trap in the P&T method and Hg was released employing a variable voltage controller and heating coil at 450°C. Sensing was managed via utilization of QCM sensors functionalized with gold, which causes amalgamation when Hg comes into contact with the gold surface. This causes a change in mass on the sensor’s surface, thereby translating to a resonant frequency shift. The characteristics of both polished and etched surface QCM sensors were studied in measuring inorganic Hg at different flow-rates (18 and 50 mL/min). The polished surface QCM sensors yielded linear ranges of detection of 5 mg/L to 10 mg/L and 1 mg/L to 10 mg/L with regression values of 0.9987 and 0.9736 for 18 mL/min and 50 mL/min respectively. The etched surface QCM sensors gave linear ranges of detection of 1 mg/L to 10 mg/L and 1 mg/L to 10 mg/L with regression values of 0.9888 and 0.9864 for 18 mL/min and 50 mL/min respectively. An etched surface QCM sensor with a flow-rate of 18 mL/min will be used for organic Hg determination due to it having at least 5 times the frequency response compared with other variations at higher flow-rates or utilizing polished surface QCM sensors. Regeneration of polished and etched surface QCM sensors was also investigated with microscopic imaging. The optimal settings of these integrated techniques were found and will be utilized in further experiments measuring concentrations of organic Hg.