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Title: Development of an in-situ microsensor for the measurements of chromium and uranium in groundwater at DOE sites. 1998 annual progress report

'The goal of this research is to develop novel electrochemical sensors for in-situ environmental monitoring of trace uranium and chromium. Such innovative remote/submersible and micromachined stripping-based devices will greatly enhance the detection of trace metals in a field setting, and should revolutionize the way such contaminants are being monitored. This report summarizes activity over the first 1.5 years of a 3-year project. This effort has led to the replacement of conventional stripping electrochemical protocols and systems with new innovative strategies for field monitoring of trace uranium and chromium, based on remotely deployable submersible sensors and micromachined hand-held total stripping analyzers. Eventually, these developments will allow to move the measurement of these metals to the field and to perform them more rapidly, reliably and inexpensively. Improved Stripping Procedures for U and Cr Traditionally, Cr and U have been measured separately using the adsorptive accumulation of their complexes with DTPA and propyl gallate (PG), respectively. To facilitate their on-site detection, the authors have developed new adsorptive stripping protocols that allow the simultaneous and rapid detection of Cr and U down to low ppb concentrations. One such new scheme involves the use of a mixed ligand (DTPA/PG) solution that allows simultaneous trace measurementsmore » in a single run (1). Numerous experimental parameters were optimized to assure that the attractive performance of the individual single-element protocols are not compromised. Simultaneous measurements in groundwater samples were documented. Alternately, they employed a single but more universal ligand (cupferron) for the simultaneous monitoring of Cr and U (2). Under optimal conditions, competition of these metals for the ligand and coadsoprtion effects were minimized, and different concentrations of the mixture components can be tolerated. A major goal and focus of this project has been the development of a miniaturized stripping analytical system, produced by micromachining technology. Such new micromachined stripping analyzers -integrating all the sample manipulations steps (including complex formation) with the adsorptive stripping measurement--will require minimal amounts of sample and reagent and will result in faster and cheaper operations. The newly designed microsystem uses an arrangement of functional modules, stacked on top of each other (to form a miniaturized flow system), including the sample and ligand/reagent reservoirs, two micro/piezo pumps, mixer, reaction coil, a silicon-based electrochemical detector and a micropotentiostat. The detector has a flow-through channel with an array of iridium microelectrodes, along with reference and counter electrodes, prepared by a photolithographic process. The size of the modules is 24 x 24 mm{sup 2}. The complete pocket-size microanalyzer has been assembled and delivered. Preliminary results are very encouraging, with both trace (ppb) Cr and U yielding well-defined signals. Yet, there are still various technical challenges, such as limited stability of the microfabricated reference.'« less
Publication Date:
OSTI Identifier:
Report Number(s):
ON: DE00013425
Resource Type:
Technical Report
Research Org:
New Mexico State Univ., Las Cruces, NM (US)
Sponsoring Org:
USDOE Office of Environmental Management (EM), Office of Science and Risk Policy
Country of Publication:
United States
44; 54; 05; Progress Report; Measuring Instruments; Measuring Methods; Remedial Action; Decontamination; Decommissioning; High-Level Radioactive Wastes; Radioactive Wastes; Chemical Wastes; PROGRESS REPORT; MEASURING INSTRUMENTS; MEASURING METHODS; REMEDIAL ACTION; DECONTAMINATION; DECOMMISSIONING; HIGH-LEVEL RADIOACTIVE WASTES; RADIOACTIVE WASTES; CHEMICAL WASTES