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
No Thumbnail Available
Date
2023-11
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Addis Ababa University
Abstract
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.
Description
Keywords
Azoxystrobin, Cow Milk, Dispersive Liquid–Liquid Microextraction, Environmental Water, Fruit, HPLC, Salt Assisted Graphene Oxide, Sulfonylurea Herbicides, Triazine Herbicide