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Title: Sampling and Sample Preparation Techniques for Trace Level Analysis of Pesticides and their Degradation Products in Water Systems of the Lower Rift Valley of Ethiopia
???metadata.dc.contributor.*???: Dr. Negussie Megersa
Prof. Jan Åke Jönsson
Prof. Theodros Solomon
Tarekegn, Berhanu
Keywords: Pesticides;Awassa Lake;Ziway Lake;Sediment;Organophosphorus pesticides;s-Triazine herbicides;Dinitrophenolic compounds;Hollow fibre
Issue Date: Feb-2008
Publisher: Addis Ababa University
Abstract: The main aim of this thesis work is to develop sample preparation and enrichment methods for the determination of various types of pesticide residues in environmental water samples. The other aspect of the study is to determine the levels of pesticide residues and their degradation products in the water systems of lower Rift Valley of Ethiopia. Accordingly, a hollow fiber supported liquid membrane extraction method for the liquid chromatographic determination of dinitrophenolic compounds at parts per trillion levels has been developed. Different variables affecting the extraction process, such as extraction time, shaking speed, acceptor pH, acceptor buffer concentration, salt content and humic acids have been studied. Enrichment factors up to 7000 times were obtained. Validation of the method including the calibration experiments and studies of the linearity of the responses in different matrices has been carried out. Good linearity was obtained in the environmental matrices evaluated. Detection limits ranging from 6.0 to 8.0 ng/L, was obtained showing that the method is suitable for trace analysis and the relative standard deviations do not exceed 7% in terms of repeatability. In addition, a new design of equilibrium hollow fibre liquid phase microextraction (HF-LPME) method was developed for the determination of freely dissolved organophosphorus pesticides (OPPs) as model compounds. In this new design, a 1.2-1.4 cm length of a hollow fibre, inserted to the end of 20 cm copper wire and impregnated with organic solvent was used to extract the freely dissolved concentration of OPPs in various water systems. This method was applied to the extraction of spiked lake and ground water samples. The ground water sample was spiked at 0.1 μg/L and 0.2 μg/L concentrations of the analytes under study and the average percentage recovery, at the two concentrations, was below 1% showing the non-depletive nature of the extraction. Good linearity (R2 = 0.991-0.996) was obtained for all of the analytes in both reagent and lake water samples. The method was found to be very simple and inexpensive, with the possibility of running hundreds of samples in parallel with very minimal expenses for the determination of freely dissolved OPPs. The levels of s-triazine herbicides and their degradation products have also been determined using a new design of time-integrating supported liquid membrane (SLM) based portable and on-site sampler. In this work the beauty of SLM technique, i.e., the combination of sampling, extraction, clean-up and enrichment processes, in a single step, has been successfully demonstrated. Besides, the levels of the residues of s-triazine herbicides and their degradation products in water samples from the selected sites of Awassa Lake have been determined. Furthermore, the levels of residues of these herbicides and their degradation products in the sediment samples of selected sites of Awassa and Ziway Lakes have been evaluated. The methods developed in this study are simple, inexpensive and environmentally friendly in terms of use of toxic organic solvents, energy utilization and worker's safety.
Appears in Collections:Thesis - Chemistry

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