Browsing by Author "Negussie Megersa"

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    Analytical Sample Preparation Methods Based on Miniaturized Extraction for Trace Level Enrichment of Selected Pesticide Residues from Environmental Water and Food Samples Utilizing High Performance Liquid Chromatographic Analysis
    (Addis Ababa University, 2023-11) Habtamu Bekele; Negussie Megersa
    The development and implementation of more environmentally friendly and sustainable microextraction techniques in recent years has provided alternative to traditional sample preparation approaches. In this thesis, we developed, optimized and validated different micro extraction methods for trace level multi residue and multiclass trace level pesticides from environmental water and food samples prior to their determination using chromatographic techniques. Salt assisted graphene oxide (GO) was utilized as a sorbent in dispersive solid phase extraction (DSPE), to enhance and extract certain s-triazine herbicides from environmental water samples. GO can generate scattered colloids in the aqueous phase and offers an extensive variety of functional groups for hydrogen bonding or electrostatic interaction with benzene ring organic compounds with functional groups comprising oxygen and nitrogen. GO was synthesized by modified Hummers method and characterized with Fourier transform infrared (FT-IR) spectroscopy. As complete collection of GO after adsorption process is difficult task, in this established salt-assisted (SA)-GO-DSPE method, it was found to be aggregated and centrifuged in the presence of NaCl. The optimum value for main parameters that influenced extraction efficiency were investigated. Under the optimized conditions, low limits of detection (LODs) (0.12–0.80 ng mL−1), limits of quantification (LOQ) (0.4–2.68 ng mL-1), and good extraction recoveries (69.06–95.53%) were obtained for simultaneous extraction of simazine, atrazine, propazine and prometryn. The relative standard deviations (RSD) of intra-day (n = 6) and inter-day (n = 9) precisions were 2.54 to 5.84% and 4.38 to 8.56%, respectively. When the method's applicability was ultimately assessed, the target analytes in the real water samples weren't detected. The proposed method is environment friendly and promising for trace analysis of other pesticides including the target herbicides in environmental water samples. Dispersive liquid–liquid microextraction based on surface floating organic droplet was designed to enable development of simple, fast, and environmentally friendly analytical technique utilizing for selective and quantitative enrichment of trace level pesticide contaminants from different fruit juice samples for subsequent detection by high pressure liquid chromatography–diode array detection (HPLC–DAD). The optimized method was investigated using spiked blank sample, and results of linearity at concentration levels from 3 to 1500 ng mL-1, with correlation coefficients (r2) ≥ 0.998 were obtained. LOD and LOQ were ranged from 1.3×10−2 to 5.3×10−2 μg L−1 and 4.2×10−2 to 1.8×10−1 μg L−1, respectively. Satisfactory accuracy, i.e, recoveries ranging from 87.23 to 99.45%, with %RSD between 1.37 and 8.39, and precision in terms of %RSD ≤ 10.78 were investigated. At the end, the method was successfully applied to analyze real fruit juice samples and target analytes were not detected in real samples. A simple, selective and fast salting out assisted liquid–liquid extraction (SALLE) technique coupled with HPLC–DAD was developed and optimized for extraction, and analysis of seven multiclass pesticide residues in pasteurized and raw cow milk samples. Under optimum conditions, for broad linear range concentration of 2–1500 μg L-1, r2 was within a range of 0.9982–0.9997. Reliable sensitivity was achieved with LODs and LOQs ranging from 0.58–2.56 ng mL-1 and 1.95–8.51 ng mL-1, respectively. While precision with intra-day and inter-day in terms of RSDs were observed in the range of 1.97–7.88% and 4.52–8.13%, respectively. The results of the precision studies reveal that good repeatability and reproducibility (RSDs < 9%) were achieved. Finally, the validated approach was effectively used to extract and determine pesticide residues in real milk matrices, however the target analytes were not detected in all samples. High density dispersive liquid–liquid microextraction method coupled HPLC-DAD was developed for extraction, enrichment and determination of six sulfonylurea herbicides; namely, metsulfuron-methyl, chlorosulfuron, niclosulfuron, prosulfuron, flazasulfuron and chlorimuron-ethyl in matrices of environmental waters. The optimum experimental parameters that influenced extraction efficiency were investigated. Under the optimized conditions, wide linear calibration curves with r2 > 0.997, LODs in the range of 0.8–1.5 ng mL−1, and LOQ in the range of 1.9–5.1 ng mL−1 were obtained. The precisions in terms of % RSDs of intra-day (n = 6) and inter-day (n = 9) were found to be 3.01 to 8.36 and 2.92 to 9.78, respectively. Applicability of the developed method was investigated by analyzing spiked tap, lake, river and underground water samples and satisfactory recoveries were obtained in the range of 84.3–101.7% with RSDs < 9.8% (n=6) and the target analytes were not detected in real samples.
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    Determination of Some Heavy Metals in two Selected Medicinal Plants Collected from Sidama Region in Masincho
    (Addis Ababa University, 2024-09-12) Zerihun Zewde; Negussie Megersa
    In this study the collected samples of P. vogeliifruitsand R. myricoides leaves were cleaned, dried in an oven and then ground topowder form. Then 0.5gof each powdered sample was digested with 4 mLof 69.72%ofHNO3 and 1 mLof 70% of HClO4at a temperature of 300℃ for 4:00hrsand 3mLof 69.72% HNO3 and 1 mLof 70% HClO4at a temperature of 300℃ for 3:00 hrs respectively. An efficient wet digestion procedure with the percentage recoveries which range from 99.33-99.97% forP. vogelii and 94.7-98.9% for R. myricoides were developed. The contents of heavy metals (Cu, Cr, Cd, Zn and Pb) in P. vogelii and R. myricoides samplesweredetermined using FAAS and the result of mean concentrationsof these metals were compared with the limit values set by WHO. The mean concentrations of the selected heavy metals were determined from triplicate samples of P. vogelii and R. myricoides herbal medicinal plantswhichwere grown in Masincho area near Yirgalem town of Sidama region.In the present study, the mean concentrations of selected heavy metals analyzed inP. vogelii and R. myricoides samplesin mg/kg were Zn (75.23± 0.038), Cu (17.68± 0.023), Pb (10..66± 0.0019),Cd (3.15± 0.0066) and Cr (BDL);and Zn (10.50± 0.0098), Cu (34.98± 0.006), Cd (8.70 ±0.0063), Pb (18.60 ±0.0072) and Cr (BDL) respectively. The contents of chromium were too lowto be measured in both sampleswhich werebelow detection limit and therefore,were not reported.The levelsof theseanalyzed metals in this study are both higher and lower just likethe concentrations of metals reported indifferent literatures in medical plant fruits and leaves.
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    Trace Enrichment of Triazine Herbicides using the Supported Liquid Membrane Extraction Technique: Applications to the Study of Waters in Ethiopian Lakes
    (Addis Ababa University, 2000-04) Negussie Megersa; Solomon, Prof. Theodros
    Methods for sample preparation of the s-triazine herbicides and their degradation products in environmental water samples using supported liquid membrane (SLM) has been developed. The herbicide compounds were selectively extracted from the flowing donor solution into a porous polytetrafluoroethylene (PTFE) membrane impregnated with nundecane, di-n-hexylether alone or with 25% 6-undecanone and 50% of n-undecane. After diffusion through the hydrophobic membrane the s-triazine herbicide compounds were irreversibly trapped into acidic acceptor phase of lower pH. The Effects of different experimental variables governing the efficiency of the extraction process have been thoroughly studied and optimized. These include the pH of both the donor and acceptor solutions, donor flow rate, ionic strengths and the analyte trapping conditions. Furthermore, the conditions for attaining maximum enrichment factor from the membrane extraction have been investigated. Selectivity of the membrane technique developed was compared with one of the most frequently used technique for sample preparation of organic pollutants, solid phase extraction (SPE) in off-line mode. It was observed that the chromatograms obtained using the SLM methodology were cleaner, indicating the good selectivity of the extraction method. The liquid membrane serves as a barrier for interfering compounds, and neutral molecules may not be enriched. The limit of detection for the extracts using SLM technique was also comparable to that of the SPE. The possibility of determining the extraction efficiency, and thus the enrichment factor, from the donor waste was also investigated. The results obtained from both the acceptor concentrate and the donor waste agreed well, which in turn indicated efficient penneation through the liquid membrane thereby giving minimum memory effects. XVI The applicability of the method for extraction of th e compounds of s-tri azine herbicides from water samples containing complex matrices was studi ed by spi king analyte sample solutions both in reagent water and ri ver water. The resulting chromatograms were not differing much, which also refl ects the selectivity of the membrane extraction developed. Water samples collected from Southern Ethiopian lakes were pre-treated and extracted in the same manner. There are a number of agricultural fi elds in this region where herbicides are periodically applied. Thus, the lake waters certainly contain considerable quantities of these residues and degradation products. The water samples, in which the phosphate buffer was dissolved to obtain neutral pH, were extracted at high donor flow rate, 5.0 mLimin, for 10 h. Low quantities of atrazine and terbutryn were identified in Awassa Lake, while only atrazine could be seen in the extracts from Chamo Lake. In both cases the concentration range of these compounds were estimated to vary from 0.02 to 0.05 Ilg/L. None of these herbicides or other s-triazine compounds could be detected in the extracts of the water samples collected from Abbaya lake. A mixture of the parent compounds and the degradation products of the s-triazine herbicides were also successfully extracted in the liquid membrane system containing carriers, e.g., trioctyl phosphine oxide (TOPO). Low detection limits were obtained for the aqueous samples spiked in river water, water containing humic acid and also in urine. Effects of the flowing donor channel, while the acceptor concentrate collected, on analyte permeation was studied in detail and better analyte results were obtained than the stagnant donor system particularly for the more polar compounds.