|Title:||Sample Preparation Based on Pressurized Liquid Extraction for the Determination of Organochlorine Pesticides Residual Status in Soil Samples of Awash Basin State Farms in Ethiopia|
|???metadata.dc.contributor.*???:||Prof. Negussie Retta|
Dr. Negussie Megersa
|Publisher:||Addis Ababa University|
|Abstract:||Method development based on pressurized liquid extraction (PLE) technique was investigated for the extraction of a- endosulfan, p-endosulfan, endosulfan sulphate, p,p' -DDT and p,p DDE from two real contaminated soil samples. PLE for 3 x 1 0 min at 100 °C was proven to be more exhaustive than Soxhlet extraction (SOX) in both soils Investigated. The use of hazardous organic solvents such as n-hexane, toluene, and diethyl ether has been avoided from PLE and clean-up. Instead, less toxic solvents have been used both at the extraction (acetone//?-heptane) and clean-up steps (ethyl acetate/«-heptane). An external glass column Florisil clean-up procedure that consumes relatively less solvent has been optimized and applied to purify soil extracts. The developed analytical procedure was validated by applying it to a certified reference soil material (CRM811 - 050), which showed a recovery of 103% total endosulfan residue versus certified values. A selective pressurized liquid extraction (SPLE) procedure capable of performing simultaneous extraction and clean-up has been demonstrated for multi-residue analysis of organochlorine pesticides (OCPs) in soil. Florisil was placed inside the extraction cell downstream the sample to remove interfering compounds. Extraction of two soil samples by SPLE gave a recovery which was over 80% for a-endosulfan, P-endosulfan, endosulfan sulphate, p,p’-DDT and -DDE compared to PLE with off-line clean-up. The developed methods were also compared with other sample preparation techniques such as solvent-shake, Soxhlet, ultrasonication and extracting syringe. The SPLE methodology has been applied for screening of 13 OCPs in twelve soil samples from different fields in Upper Awash Agio Industry Enterprise (UAAIE). Quantitative and qualitative analyses were done using a dual column GC-ECDs and GC-MSD respectively. The main contaminants that were identified comprised previously used persistent organic pollutants (p,-DDT, dieldrin and endrin ), currently used insecticides (a-and p-endosulfan) and degradation products (p,-DDE and endosulfan sulfate). Endosulfan and DDT were detected in substantial amounts with £DDT up to 230 ng/ g and endosulfan up to 56,000 ng/g of dry weight, which could be a potential threat to the environment. The efficiency of the SPLE was evaluated by aging a mixture of 13 OCPs in six different soil types for a period of one week to nine weeks. Inspite of the difference in aging time and soil type, recoveries about 100% were achieved for most of OCPs spiked into five soil types (TS, NS, GS, WS and RGC) . No apparent positive or negative correlation was perceptible between soil characteristics (organic matter and clay content) and extractability of aged OCPs, which signifies exhaustiveness of extraction method . However, recovery was considerably minimized (< 75 %) in the case of YGC soil. This emphasizes the importance of optimizing the extraction parameters due to distinct properties of analyte-matrix interactions.|
|Description:||A Thesis Submitted to the School of Graduate Studies of Addis Ababa University in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Chemistry.|
|Appears in Collections:||Thesis - Chemistry|
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