Currently, water quality monitoring for heavy metal contaminants is handled by sophisticated instruments such as ICP-MS, GC/LC-MS, and AAS that require reagent preparation by laboratory personnel. This approach requires random grab sample collection and transportation for lab analysis. The result is, of course, a snapshot of the water quality at a particular time and place. We have therefore been developing miniaturized and inexpensive sensors suitable for long-term real-time monitoring with reduced need for manual intervention. Practical applications include sensor networks to monitor the drinking water distribution grid, industrial wastewater effluents, and even rivers and lakes.Amongst the biggest challenges for remote sensors are the issues of in-field device calibration and sample pretreatment. To address these two challenges, we have investigated use of coulometric stripping analysis for a calibration-free micro-fabricated electrochemical sensor (CF-MES), that is based on Faraday's law of electrolysis (Q=nFN). In the determination of copper and mercury, this platform's theoretical LOD (3s) is 6ppb in a 1.83 �L sample (180 femtomoles). For more negatively reduced metals (e.g., Pb, Cd), the H2O2 product of O2 reduction interferes with stripping analysis; hence, the reliance of many electrochemical analysis techniques on pretreatments to remove dissolved oxygen (DO). We have therefore designed a physical/electrochemical system to explore the possibility of remote in-line oxygen removal, utilizing a silver cathode to electrochemically reduce DO in an adjacent chamber (fluidically isolated from the sample stream by an O2 permeable membrane). The resulting concentration gradient supports O2 diffusion from the sample stream into this O2 depleted chamber. The presented work will summarize our CF-MES for heavy metal contaminants, and describe the design and evaluation of a prototype in-line oxygen remover suitable for miniaturization. The current prototype requires <100�A for continuous operation; and preliminary results indicate removal of a significant fraction of DO.

Electrochemical and microfabrication strategies for remotely operated smart chemical sensors: The dual challenges of sample preparation and calibrationless measurements

246th National Meeting (2013)

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