| The contamination of natural resources by human activity can have severe socio-economical impacts. Environmental analytical chemistry plays an essential role in the solving of these environmental problems. Micro-total analysis system (μTAS) has enabled the miniaturization and simplification of environmental contaminant detection methods. Reduced reagent and sample consumption, speed of analysis, and field portability are only a few of the advantagesμTAS systems provide, Centrifugal microfluidics have the added advantages of using centrifugal force for moving liquids, thereby avoiding solvent and filtration problems encountered with electro-osmotic flow typically used inμTAS manifolds. These properties suggest that centrifugalμTAS systems may offer many advantages as analysis platforms for the on-site analysis of a variety of important environmental pollutants.In this thesis, several microscale analytical techniques based on cetrifugal microfluidic have been developed with the objective of minimizing the number of sample preparation steps, avoiding the use of organic solvents and reducing the size of the samples required for an envrionmental analysis as well as increasing the speed of analyses. The main contributions are summarized and presented as follows:A centrifugal microfluidic device was developed for the rapid sequential determination of two critical environmental species, nitrate and nitrite, in water samples. The nitrate is reduced to nitrite and the nitrite is derivatized. The analytes are determined spectrophotometrically through the disc with a 1.4mm pathlength. The detection limits are 0.05 and 0.16μg/mL for nitrite and nitrate respectively. The use of powdered reagents, the 100μL sample required and the design of the device suggest that it would be suitable for field use.The liquid extraction of oil and grease (OG) from water and soil samples on the centrifugal microfluidic devices is presented. Magnetically driven sample preparation unit is integrated on the centrifugal device with a sedimentation/filtration unit in the case of soil analysis and finally with an integrated detection cell for both liquid and solid analysis. Tetrachloroethylene (C2Cl4) is used as the extractant as a Freon 113 or carbon tetrachloride substitute. OG was tested by IR spectrophotography, and 11μg/mL of detection limit was obtained.In chapter 4, a centrifugal microfluidic device was fabricated with studying the preparation of solid phase extraction column. Cr3+ and Cr6+ were separated on this device and detected by ICP-MS. The system could process up to 8 samples simultaneously in short time, providing easy to use. This procedure allows for a rapid and good separation and quantification, only 100μL of sample and reagents was used, and the detection limit for Cr6+ is 2 ng/mL.The centrifugal microfluidic SPE discs were modified to allow their seperation of waste and elution and coupling to absorption spectrometers. We present a method for a passive flow switching valve on a centrifugal microfluidic platform, which controls the direction of a flowing liquid at a junction where a common inlet and two outlet channels meet. Switching of the flow can be performed by relying on the Coriolis force that changes its pointing direction, perpendicular to the flow direction, with the rotational direction a disk in a double layered arrangement at a symmetrical junction. This flow-switch valve, combined with solid phase extraction technique, followed by elution with ethanol, was applied in the extraction of phenol in water.Chapter 6 presents a novel miniaturised magnetically actuated liquid-solid extraction unit integrated in tandem with a filtration unit and a detection unit on a single centrifugal microfluidic device. A demonstration analyte, pyrene, was rapidly extracted and quantified by UV-absorbance from multiple soil samples. The system showed excellent performance for a system designed for field use. Characterization of two types of passive valves was performed along with an extraction time efficiency study. The system provides a factor of 150 reduction in sample weights and extraction solvent volumes and provides statistically similar recoveries to the conventional method with a pyrene detection limit of lppm (0.03μg absolute detection limit).Finally, a centrifugal microfluidic device system for enzyme inhibition techniques in relation to pesticide analysis is discussed. Two discs were designed for pesticide carbofuran anlysis in vegetable and soil sample respectily. By rotation of the disc at sufficient speed, the extractant mixed with the sample is capable of extracting pesticide from the sample. Furthermore, inhibition of esterase enzyme activities by carbofuran was performed in the following reservior and determined by spectrophotometry using 1-Naphthyl acetate substrate and Fast blue B salt chromatic reagent in the third reservior. 11μg/mL of detection limit was obtained. The entire process, including extraction, two steps of reaction was performed automatly on the centrifugal platform. The devices are low-cost, simple to use and assemble.
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