The development and characterization of miniature spectrometers for measuring the redox status of environmental samples Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/1g05fd76r

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  • A spectrometer, here denoted a Simple, Low-power, Inexpensive. Microcontroller-based or SLIM spectrometer. was developed that exploits the small size and low cost of solid-state electronic devices. This approach results in customizable spectrometers that are considerably less expensive and smaller than traditional instrumentation. The performance of the SLIM spectrometer was evaluated and compared to that of a commercial spectrophotometer. Thionine was the analyte, and the detection limit was ~0.2 micromolar with a 1.5-mm path length flow cell. Another device, here denoted a Sub-surface Probe for the Evaluation of Anaerobic Regions or SPEAR, was also developed. The SPEAR is inserted directly into the ground or sediment and automatically records depth-resolved redox information in real time. The device is based on membrane sampling devices or "peepers" that allow subsurface samples to be collected without changing the redox speciation of sensitive species. Miniature spectrometers incorporated in the probe measure the absorbance of the redox indicators immobilized on clear membranes to track the redox status in situ. The device was tested with the redox indicator thionine in a waterlogged soil in the Willamette Valley of Oregon. The reducing region of the pore water was observed over a two and a half week period in late March. A device for monitoring the absorbance of an immobilized redox indicator, in direct contact with a sample inside a transparent microcosm bottle or hioreactor, through the wall of the enclosure has been developed. In this device, denoted as Spectrometer for Non-invasive Anaerobic Reflectance Evaluation or SNARE, the indicator is immobilized in a film or membrane, which is attached to a circular magnet. This disk is placed inside the laboratory vessel, and reductants or oxidants in the solution interact with the immobilized indicator causing a change in its color. Another magnet, imbedded in the external probe, attracts this disc to the side of the container and aligns the probe and disc in the proper orientation. The operation of this device was demonstrated with the redox indicator thionine to determine the redox status of a sample containing an enriched culture in which the anaerobic degradation of chlorinated ethenes was occurring.
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