Date of Award

1-2001

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Environmental Science

First Advisor

Dr Mohamed Sayed Ibrahim

Second Advisor

Dr. Alia Abd Elaziz Salem

Third Advisor

Dr. Naeem Akhar Rabi

Abstract

Buprofezin [2-[(1, 1-dimethylethyl)imino]tetrahydro-3-(1-methylethyl)-5-phenyl-4H-1,3,5-thiadiazin-4-one] is a thiadiazine insect regulator and molting inhibitor that has a persistent larvicidal action against some Coleoptera and Hemiptera and effectively controls harmful insect pests including the brown rice planthopper Nilaparvata lugens and the greenhouse whitefly Trialeurodes vaporaiorum. However, amitraz (IUPAC name: N-methylbis(2,4-xylyliminomethyl) amine belongs to the family of the triazapentadienes. It is a non-systemic acaricide and insecticide which has contact and respiratory action. Amitraz is active against a wide range of larvae and phytophagous insects. Its properties have long been known. Additionally, amitraz is often used against varroasis disease, caused by the mite Varroa Jacobsoni and affects Apis Mellifera. Amitraz shows a high activity against V.jacobsoni, and low toxicity for bees.

In this thesis, the adsorptive voltammetric behavior of buprofezin and amitraz on hanging mercury drop electrode (HMDE) was investigated. The thesis also deals with the development of a cathodic stripping voltammetric assay for the determination of these pesticides and its application to determination of the investigated compounds in soil and water. Furthermore, the effect of heat on the stability/degradation of amitraz as well as the electrochemical degradation of buprofezin were investigated.

In what follows, a brief description of the different chapters reported in this thesis is given:

1. In chapter I, a general literature survey on the previous quantitative determination studies on pesticides as well as the degradation studies of pesticides is reviewed.

2. In chapter II, the experimental part involves the preparation of the various solution. It also includes description of the instrumentation used in the present measurements which cover the diverse electrochemical tools:

(a) Cyclic voltammetry (CV).

(b) Cathodic adsorptive stripping voltammetry (CASV).

(c) UV-Vis and Infra red spectroscopy.

(d) Electrochemical degradation.

3. In chapter III, the surface activity and redox behavior of buprofezin at HMDE, were studied by cyclic voltammetry (CV) in different buffer solutions. The shape and height of CV peaks depend on various parameters such as, pH, adsorption time, and scan rate. The CV behavior of buprofezin shows a single irreversible cathodic peak over the whole pH range (3.0-12.0). The cathodic peak is due to the reduction of the exocyclic >C=N- group of the adsorbed buprofezin species. No oxidation peak is observed in the anodic direction, which is indicative of the irreversibility of the buprofezin reduction. This phenomenon can be exploited for the electroanalytical determination of buprofezin with the aid of adsorption accumulation in stripping voltammetry. In the present work cathodic adsorptive stripping voltammetric technique is applied for the determination of buprofezin in model samples as well as in soil and water.

Buprofezin was treated electrochemically using platinum as the working electrode that was subjected to an intense prolonged illumination through a UV-lamp. In the later case, the degradation in the aqueous medium was monitored using UV-Vis spectrometry.

This part was published in Analytica Chemica Acta 432 (2001), 21-26 under the title: "Voltammetric determination of the insecticide buprofezin in soil and water".

4. In chapter IV, the cyclic voltmmetric behavior of amitraz was studied in solutions with different pH values. In acidic and alkaline solutions the CV exhibit one irreversible cathodic peak. According to the molecular structure of amitraz this peak corresponds to the cathodic reduction of the azomethine group (-CH=N-) of adsorbed amitraz species via the well known 2e-/2H+ reduction mechanism of the azomethine compounds. However, in neutral and slightly alkaline solutions (7.1 ≤ pH ≥ 9.1) the CV are characterized by two consecutive cathodic peaks. The appearance of the second reduction peak, close to the hydrogen discharge potential, can be assigned to the reduction of the carbonyl compound, which formed as a result of amitraz hydrolysis. The adsorption of amitraz on the HMDE can, consequently, be used as an effective preconcentration step before quantitative measurements are undertaken. Owing to its better analytical characteristics, the voltammetric technique used in the stripping step was the differential pulse stripping voltammetry (DPSV). The method was applied to the determination of amitraz in spiked soil and water. The candidate also studied the effect of heat on the stability/degradation of amitraz. In this case, amitraz is injected to soil sample, subjected to control heating and the stability/degradation was monitored using IR-spectrophotometry and cathodic stripping followed by differential pulse voltammetry.

This part was approved for publishing in Microchemica Acta (2001)

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