Date of Award

4-1998

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Environmental Science

First Advisor

Tarek Ghonima

Second Advisor

Mostafa M. Kamal

Third Advisor

Dr. Meshgan M. AI-Awar

Abstract

Chlorpyrifos is a member of the organophosphorus class of insecticides. This class of insecticides has become one of the most widely under groups of pest control chemicals. Early organophosphorus compounds that were found to be efficacious for insect control and thus brought into widespread use, e.g. Chlorpyrifos, Parathion and Malathion. The broad-spectrum insecticidal properties of Chlorpyrifos indicated that it possessed substantial commercial potential to use against a wide variety of important arthropod pest via a number of commercialized products. Therefore, it is employed in a wide variety of agricultural and specially pest control scenarious and other arthropod pests threatening production of fiber and maintenance of human health. This thesis involves the polarographic and voltammetric behaviour of Chlorpyrifos at the mercury electrode surface. The work was developed for application of the differential pulse-polarography (DPP) and cathodic adsorptive stripping voltammetry (DP-CASV) for determination of Chlorpyrifos in some water samples and in tomato plant.

Chapter I of the thesis includes the environmental impact, sequences for pesticide residue analysis and a literature survey about the preconcentration and analysis of organochloro and organophosphorous pesticides. Also, the objective of this work is included.

The experimental part of the thesis is presented in Chapter II. It includes the chemicals and materials used, the methods of preparation of the various solutions and the methods of preparation of the compound in various water samples. The instruments used for polarographic and voltammetric analysis are included. The general procedures for polarographic and voltammetric analysis as well as, for the extraction of the insecticide from water and plant samples were presented.

In Chapter III the differential pulse polarographic (OPP) behaviour of Chlorpyrifos (CP) was investigated over a wide range of pH (pH 1.8-10.1). CP compound displays a well resolved cathodic reduction peak at -1.2 V vs Ag/AgCl (pH 3.2). This peak is probably corresponding to the reduction of the \/ C = N - centre of the pyridyl moiety. The effect of solution and operational parameters on the sensitivity of the OPP peak was carefully examined in order to select the optimum conditions for determination of the CP compound. Under the optimum conditions the reduction response gives a linear calibration curve over a concentration range of 9.70 x 10-7 - 6.92 x 10-6 M and the detection limit was found to be 8.7 x 10-7 M. The effects of some diverse metal ions, anions and other organophosphorus insecticide on the determination of CP compound were studied. The applicability of OPP for determination of the CP insecticide in the commercial sample as well as in some irrigation water (treated waste water and underground water) was detected.

The cyclic voltammetric (CY) and the differential pulse – cathodic adsorptive stripping voltammetric (DP-CASY) behaviour of the CP compound at Hg electrode were presented in Chapter IY. The CV indicates that the oxidized form of the CP compound is strongly adsorbed at the mercury electrode surface, which is the ideal condition to apply the OP-CASY method for trace analysis of the CP compound. Under the optimum conditions (pH 5.01, 10 mV/s scan rate, 50 mV pulse amplitude, -0.4 V adsorption time and 180-240 s adsorption time) the tested compound was detected down to 1 x 10-8 mol/L using DP-CASV method. Also, the method was applied for determination of the CP compound in some water samples (tape water, underground water and treated waste water). The degree of recoveries of the CP prepared in various water samples are in the acceptable range (91-103%) except in case of underground water the degree of recovery of CP is relatively low (76-81 %). A method of analysis was developed for determination of CP in tomato tissue, it was found that 2.66 x 10-7 mol/L CP is the concentration of CP in tomato tissue and it could be determined down to 0.018 mg CP/kg tomato.

It can be concluded that the Chlorpyrifos compound could be determined using DPP with a detection limit of 8.7 x 10-7 mol/L. However, the trace analysis of CP could be possible down to 1 x 10-8 mol/ L (0.0034 mg/ L) using DP-CASV technique.

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