Miniaturized Electrochemical Sensor for Cr(VI) in Groundwater and Surface Water

This project will utilize photolithography and microfabrication in the assembly of a Cr(VI) monitoring device that is compact, portable, and cost effective. The proposed sensor will be a self-contained laboratory that samples, analyzes, and stores the results of onsite testing under a variety of sampling conditions. The device will rely on the pressure-driven introduction of aqueous samples that will be combined with a small, specific volume of electrolyte. Analyte streams of arbitrary ionic strength and composition will be sampled with minimal pretreatment. The use of a microelectrode array sensor chip will allow for increased sensitivity via enhanced diffusion of the analyte to the sensor element. In addition, use of a miniaturized detector will reduce solution waste during testing. Eltron Research, Inc.'s proposed electrochemical detection scheme allows for the use of simple, inexpensive instrumentation that is capable of the remote monitoring of groundwater and surface waters for Cr contamination. Phase II will focus on the optimization of the proposed Cr(VI) sensor in addition to the assembly and design of a prototype unit for field analysis of groundwater and surface waters using minimal analyte and supporting electrolyte. In Phase I, Eltron Research Inc., successfully demonstrated that self-assembled monolayer (SAM) modified microelectrode arrays could be used for the electrochemical detection of Cr(VI) in aqueous solutions. Cr(VI) solutions with concentrations varying from 0.1 ppb to 100 ppb could be detected using a sensitive electrochemical method. Using photolithography, a robust microelectrode array was fabricated and incorporated into a microfluidic flow cell for Cr(VI) detection. Furthermore, this flow cell was successfully coupled to a peristaltic pump to introduce analyte and supporting electrolyte for Cr(VI) detection, and was interfaced to benchtop electrochemical instrumentation (a potentiostat) for potential use in long-term monitoring situations. The performance of the miniaturized Cr(VI) detector was studied as a function of such variables as pH, supporting electrolyte concentration, SAM deposition time, Cr(VI) exposure time, electrolyte type, and Cr(VI) concentration. The electrochemical detection of Cr(VI) in water is a cost-effective method for long-term, remote monitoring of suspected environmental contamination sites. This approach could find general use in both specific U.S. Environmental Protection Agency applications and those of the private sector; for example, the monitoring of Cr waste in the electroplating industry. Other industries requiring wastewater monitoring for hexavalent chromium include metal processing, galvanic plants, tanneries, wood preservation, chemical manufacturing, aerospace, and electronics.