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Addis Ababa University Libraries Electronic Thesis and Dissertations: AAU-ETD! >
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Please use this identifier to cite or link to this item:
http://hdl.handle.net/123456789/1965
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| 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 |
| Authors: | AHMED, HUSSEN |
| Advisors: | Prof. Negussie Retta
Dr. Negussie Megersa |
| Copyright: | 2007 |
| Date Added: | 22-Jan-2009 |
| Publisher: | Addis Ababa University |
| Abstract: | Method development based on pressurized liquid extraction (PLE) technique was investigated
for the extraction of α- endosulfan, β-endosulfan, endosulfan sulphate, p,p’-DDT and p,p’-
DDE from two real contaminated soil samples. PLE for 3 x 10 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/n-heptane) and clean-up steps (ethyl acetate/n-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 α-endosulfan, β-endosulfan, endosulfan
sulphate, p,p’-DDT and p,p’-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.
xvii
The SPLE methodology has been applied for screening of 13 OCPs in twelve soil samples
from different fields in Upper Awash Agro 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,p’-DDT, dieldrin and endrin), currently used insecticides (α-and β-endosulfan)
and degradation products (p,p’-DDE and endosulfan sulfate). Endosulfan and DDT were
detected in substantial amounts with ΣDDT up to 230 ng/g and Σendosulfan 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 |
| URI: | http://hdl.handle.net/123456789/1965 |
| Appears in: | Thesis - Chemistry
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