Micro total analysis system for in-situ and autonomous spectrophotometric monitoring of iron in groundwater Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/kp78gk363

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  • We have developed a compact micro total analysis system (μTAS) to serve as a platform for in-situ spectrophotometric water quality monitoring. Individual fluidic, optical, and electrical components were designed, developed, and characterized. These components were combined in both an integrated (single lithographic “chip-based” platform) and a modular manner. The microfluidic components include a modular microfabricated filter chip, a miniature reagent storage bag, an integrated micromixer & absorbance flow cell, and modular micropumps. Optical and electrical components include a miniature spectrometer, a white LED, fiber optics, SMA fiber couplers, a processor, motor & LED drivers, spectrometer circuitry, EEPROM memory, and AAA batteries. Both a partial (fluidics but not all optics or electronics) and complete system were tested in the laboratory, by determining total iron (1,10-orthophenanthroline method), with environmental and surrogate samples. These measurements compared well to results from the same samples measured with a benchtop (cuvette and spectrometer) system (calibration slopes 3.4 x 10-3 AU/μM; 10% difference for an environmental sample). For the complete μTAS, the detection limit for iron in the laboratory samples was estimated to be 1 μM. For the partial system, the RSD of the absorbance of a 38.4 μM standard was 2.8% (n = 13) and the estimated detection limit for a wetland sample was 2 μM. To demonstrate the utility of the device, a groundwater monitoring well, designed both for environmental sampling and device deployment, was installed in a seasonally wet prairie to measure iron. The device was deployed in the well and samples were taken to verify system performance. Due to a software malfunction, the device batteries were drained after 2.5 days of operation. During this time the device performed adequately, although all iron levels were below the detection limits of both the μTAS and the benchtop system. This work is the first demonstration of an in-situ μTAS for water quality monitoring, the first microfluidic measurement of environmental iron, the first use of an internal dye standard to determine the dilution factor, and one of the smallest complete μTAS developed thus far.
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