Date of Award

12-1999

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Environmental Science

First Advisor

Mustafa M. Kamal

Second Advisor

Dr. Meshgan M. AI-Awar

Third Advisor

Dr. M. S. Ibrahim

Abstract

A challenging problem facing the determination of phenoxy acid herbicides in samples is their low UV absorptivity and the interference associated with the matrix in which these analytes exist. This thesis is concerned with improving the detection limits of this group of herbicid as well as reduce or eliminate interference associated with the sample matrix.

Native phenoxy acid herbicides could be analyzed by high performance liquid chromatography (HPLC) with ultraviolet detection. Phenoxy herbicides were analyzed by HPLC employing a gradient conditions that allowed baseline resolution of all analytes used in this study in approximately 20 min. However, the average detection limit of these herbicides using such conditions and a UV detector was only 0.5 x 10-6 M. This detection limit was higher than the concentration at which these herbicides exit environmentally.

The procedure developed in this study for improving the detection limit of the studied herbicides involved the derivatization of analytes with a fluorescing derivatization reagents such as 2-aminobenzamide and 1-aminonaphthol-4-sulfonic acid. The procedure was based on the coupling between the carboxylic acid group of the analytes and the amine group of the derivatization reagent. As a result of this coupling an amide bond was formed between the analytes and the derivatization reagents. The procedure required the utility of a condensation agent such as benzatriazol-1-yloxy tris (dimethylamino) phosphonium hexafluorophosphate (BOP). The utility of this condensation reagent allowed the completion of the labelling in approximately 40-50 min for all analytes. The labelling with these derivatization reagent allowed better detection limit as well as separation. Initially, 2-aminobenzamide was used as a derivatization reagent and the derivatization for all analytes was determined to be efficient as was deduced from HPLC and mass spectrometric analysis. However, the derivatization with this derivatization reagent reduced the resolution of the separation and varying the separation conditions did not result in attaining baseline resolution of all analytes in a single analysis. Therefore, l-aminonaphthol-4-sulfonic acid was used instead as a derivatization reagent and it proved to be more effective in providing baseline resolution for all analytes. 1-aminonaphthol-4-sulfonic acid derivatized herbicides were baseline resolved by HPLC and the average detection limits of all analytes was approximately 1 x 10-8 M. This is a two order of magnitudes improvement over the detection limit of native phenoxy acid herbicides by UV detector. Moreover, the separation of those labelled phenoxy acid herbicides was attained in shorter time. The separation of labelled herbicides was achieved in less than 12 min relative to the 20 min needed for the separation of native phenoxy acid herbicides.

This developed procedure was utilized for studying the uptake of crops and soil accumulation for phenoxy acid herbicides. First, the movement of phenoxy acid herbicides through the UAE soil was conducted employing this developed procedure. The method allowed the sensitive monitoring of the movement of these phenoxy in the UAE soil. The study was conducted to monitor the movement of these phenoxy acid herbicides under field conditions. The method demonstrated the weak interaction between the analytes and the UAE soil since the highest concentration of these herbicides were determined to exist in the bottom layer, thus supporting the expected weak interaction between the analytes and the soil.

Second, the method was also employed to study the uptake of plants for these phenoxy acid herbicides. The uptake of plants for these herbicides could not be monitored by UV detectors due to high interference associated with the matrix in which the final sample existed. Using the developed method substantially eliminated the interference and allowed the determination of herbicides in the roots and leaves of plants treated with these herbicides. The study demonstrated differential uptake of plants to these herbicides as was dictated by the amount determined in the leaves and roots.

The developed method improved detection limits by two orders of magnitudes, eliminated interference associated with sample matrix, allowed the studying of movement of phenoxy acid herbicides through DAB soil, and permitted the studying of plant uptake of the phenoxy herbicides.

Share

COinS