Trace Level Sample Preparation Techniques for Selective Extraction of Pesticide Residues In Environmental and Food Samples, and Their Quantitative Removal From Contaminated Waters Utilizing Typha Latifolia Plant Parts
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Date
2018-06-05
Authors
Tolcha, Teshome
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Addis Ababa University
Abstract
The objective of this thesis work is to develop various miniaturized and green sample preparation techniques for the determination of pesticide residues in matrices of different origin and the quantitative removal of pesticides from contaminated water. In this research work, an efficient and sensitive high desnsity based dispersive liquid-liquid microextraction (HD-DLLME) method coupled with gas chromatographic mass spectrometric detection (GC-MS) for the simultaneous determination of pesticide residues in water and sugarcane juice has been developed and validated. The effects of type and volume of extraction solvent, type and volume of disperser solvent, centrifuging speed and time, extraction time, sample pH and absence or presence of electrolytes was examined. The performance of the analytical technique was evaluated by extracting spiked distilled and de-ionized water at 2.5 and 5 μg/L. For 5 mL sample of water and sugarcane juice the method offers good linearity (R2 ≥ 0.991), repeatability (0.73–5.3%) and reproducibility (1.1–8.7%). The limit of detections (LODs) ranges from 0.005 to 0.01 μg/L. This method was successfully applied for simultaneous quantitative and qualitative determination of target analytes in water and sugarcane samples showing excellent relative recoveries (80.4–114%).
Modified salting-out-assisted liquid-liquid extraction (SALLE) followed by preconcentration using low density based dispersive liquid-liquid microextraction (LD-DLLME) for the qualitative and quantitative determination of atrazine, diazinon, ametryn, terbutryn, chlorpyrifos, dimetham-etryn, 4,4'-dichlorodiphenyldichloroethylene, 4,4'-dichlorodiphenyldichloroethane and 4,4'-dichloro-diphenyltrichloro-ethane residues in sugar and soil samples was also developed. Various parameters affecting the extraction process such as type and volume of organic solvent, type and amount of salt, extraction time, pH of the sample solution, centrifugation speed and time were optimized. Under optimum conditions, the method offers good linear range with regression coefficients of 0.992–0.999, low limits of detection of 0.01–0.3 μg/kg. The precision (intra- and inter-day) of the method expressed as relative standard deviations (RSD) at 12.5 and 50 μg/kg were below 10% in both matrices. The recoveries obtained from spiked sugar and soil samples at 12.5 and 50 μg/kg were ranged from 79.0 to 111%. The soil sample was contaminated by atrazine and ametryn at concentrations of 0.29 and 0.23 μg/kg respectively. ii
A high density supercritical CO2 (sc-CO2) extraction method has also been developed for extraction of atrazine, 2,4´-DDD, 4,4´-DDT and endrin from onion samples. The extraction volume of sc-CO2 and temperature were also considered as potential parameters and optimized. It was observed that increasing density of sc-CO2 increases extraction recovery of all target analytes and the effect is significant for endrin and 2,4´-DDD. The optimum conditions were found to be 29 mL, 0.9 g /mL, 53 oC for volume of sc–CO2, density sc-CO2 and temperature, respectively. Matrix matched calibration curves showed satisfactory linearity (R2 ≥ 0.994). LODs ranging from 0.2 to 2 μg/kg were achieved and precision studies showed RSDs lower than 11% and recoveries in the range of 80.3 to 103%. The method was successfully applied to onion sample and none of the target analytes were found in the sample investigated. Therefore, the developed method can be used for trace analysis of the pesticide residues studied and other pollutants having related physical and chemical properties.
Similarly, multivariate optimization of combined static and dynamic mode sc-CO2 extraction method for trace analysis of atrazine, diazinon, chlorthalonil and deltametryn residues in honey has been systematically optimized and validated. The parametrs that affect the extractability of relatively polar and non-polar pesticides including static time, temperature and pressure were optimized. The optimum extraction conditions were 11.5 min contact time in static mode, 252 bar and 70 oC. The proposed method has good linearity (≥ 0.998), and LODs ranging from 5.0 to 9.0 μg/kg. The precision study at two concentration levels, 250 and 1000 μg/kg was found to be in the range of 2.3–4.2% for intra-day (n = 3) and 2.1–8.0% for inter-day precisions (n = 3). The proposed method was successfully applied for selective extraction of the target compounds from complex matrices and the results obtained clearly indiacated there is no significant matrix effect on quantitative analysis of the target analytes.
Removal of atrazine, diazinon, chlorothalonil, ametryn, malathion, chlorpyrifos and dimethametryn from aqueous solutions was also investigated utilizing Typha latifolia. The characteristic surface chemistry of stem, leaf and flower of the Typha latifolia plant were analyzed by FT-IR analysis. Different experimental parameters including pH, shaking speed, contact time, adsorbent dose and initial pesticide concentration were studied. Equilibrium and kinetic models for pesticide sorption were studied by considering the effects of concentration and contact time at iii
the optimum conditions for each of the Typha latifolia plant parts. Results of the sorption equilibria were found to fit to the Langmuir isotherm model than the Freundlich adsorption model indicating monolayer homogeneous surface conditions for most analytes in all adsorbents. Atrazine, malathion and chloropyrifos for stem and atrazine, ametryn, chlorothalonil and dimethametryn for leaf powder as adsorbent fit to better Freundlich adsorption model, indicating monolayer sorption with a heterogeneous energetic distribution of active sites. On the other hand, kinetics of all pesticides, under study, sorption on the Typa latifolia was well defined by the pseudo-second order model. The results obtained showed that the use of this plant can be considered as one of the most promising, easily accessible and low cost adsorbent.
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Keywords
Classification of Pesticides, Organochlorine Pesticides, Adsorption Isotherms, Temperature, Sorption Kinetics