Flow Injection methods for the Determination of Pesticides in natural water Samples Using chemiluminescence / Spectrophotometric detection

Abstract

In recent years, the increasing number of pollutants being detected in surface water has raised concern about the contamination of water resources. Pesticides contamination of soil, food and waters has become a serious problem. Pesticides are widely used for the control of insects, fungi, bacteria, weeds, nematodes, rodents and other pests. However, despite their many merits, pesticides are some of the most toxic, environmentally stable and mobile substances in the environment. Their excessive use has deleterious effects on humans and the environment; their presence in food is particularly dangerous. Pesticide exposure can cause a variety of adverse health effects. These effects can range from simple irritation of the skin and eyes to more severe effects such as affecting the nervous system, mimicking hormones causing, reproductive problems and cancer. Strong evidence also exists for other negative outcomes from pesticide exposure including neurological defects, birth defects and neuro–developmental disorder. Pesticides are categorized into four main substituents: i) herbicides, ii) fungicides, iii) insecticides and iv) bactericides. In 2006 and 2008, the world used approximately 5.2 billion pounds of pesticides with herbicides constituting most of the world pesticide use at 40% followed by insecticides and fungicides with totals of 17 and 10% respectively. Therefore, the developments of simple and sensitive methods for the monitoring of pesticides are of great importance for the purpose. Chemiluminescence (CL) is defined as the electromagnetic radiation (ultraviolet, visible, or infrared) produced when a chemical reaction yields an electronically excited intermediate or product. The light intensity is directly related to the analyte concentration, thus allowing precise and sensitive quantitative analysis. The main attractions of CL for vii biochemical analysis show excellent sensitivity over a wide linear range and low limits of detection. There are many inorganic and organic chemical reactions that produce CL in the liquid phase and some of these CL systems are luminol, lucigenin, morphine, codeine, pyrogallol, acridinium esters, acidic potassium permanganate and tris(2,2/ -bipyridyl) Ruthenium(II). Luminol, lucigenin, tris(2,2/ –bipyridyl) Ruthenium(II), KMnO4 and cerium(IV) sulfate are the most commonly employed CL reagents and find wide applications in analytical chemistry and chemical analysis. Transition metals in uncommon oxidation states such as silver(III), copper(III) and nickel(IV) have been exploited in the CL systems as oxidizing agents. Flow injection analysis (FIA) is based on the injection of a small volume of liquid sample into a moving non-segmented continuous carrier stream of a suitable liquid. The injected sample becomes a part of a continuously moving stream and forms a zone. The processed sample carrying stream is then finally transported towards a detector that continuously records the absorbance, emission, electrode potential or other physical parameter. This thesis concerns research work in the area of FIA in conjunction with CL and UV-Visible spectrophotometric detectors for the determination of pesticides in natural water samples. The work presented in this thesis is divided in ten chapters. The first chapter is devoted to the knowledge on the pesticides, its classification, toxicology, handling of water samples, luminescence, CL and its reagents with their analytical applications related to pesticides analysis in natural water samples. The FIA with its basic components and analytical applications are also presented in tabulated form. The second chapter describes CL instrumentation including a brief introduction and characteristics of photomultiplier tube (PMT), continuous flow methods, glass spiral flow cells and a test method for the determination of manganese(II) using luminol– diperiodatoargentate(III) (DPA) system to examine the performance of PMT detector in FI-CL mode. The third chapter describes a FI-CL method for the determination of Mn2+, maneb and mancozeb fungicides based on the catalytic effect of Mn2+ on the oxidation of viii lucigenin and dissolved oxygen in a basic solution. The Tween-20 surfactant has been reported for the first time to enhance lucigenin CL intensity in the presence of Mn2+ and maneb and mancozeb. The effect of thirty-two other pesticides (fungicides, herbicides and insecticides) was also investigated on this CL system. The fourth chapter describes the development of a simple FI-CL system for the determination of thiram and aminocarb pesticides in natural water samples based on the strong enhancing effects of these pesticides on the Ru(bipy)3 2+ –DPA CL system. Thiram could be determined in the presence of aminocarb using Triton X-100. The possible CL reaction mechanism is also discussed briefly. The fifth chapter describes a FI-CL method for the determination of thiabendazole (TBZ) fungicide based on its enhancement effect on diperiodatocuprate(III) (DPC) – H2SO4 CL reaction. The method was successfully applied for the determination of TBZ in water samples using dispersive liquid–liquid micro-extraction (DLLME). The possible CL reaction mechanism for DPC–sulphuric acid–TBZ is also discussed. The sixth chapter describes a simple and sensitive CL procedure for the determination of cyromazine (CYR) using FI technique. CYR has strong enhancing effect on the CL reaction of DPA in H2SO4 medium. Interference from chloride ions could be eliminated by using SPE procedure or incorporating an in-line ion exchange resin column (IERC). The CL mechanism of DPA–H2SO4–CYR system was also discussed briefly. The seventh chapter describes a FI-CL method devised for the analysis of thiram in natural water samples. The CL intensity is enhanced when thiram is oxidized with potassium bromate under strong acidic conditions subsequently using quinine as a sensitizer. The proposed method was applied for thiram analysis in spiked natural water samples and results obtained were satisfactory with the previously reported HPLC method. A brief discussion on the possible CL reaction mechanism between thiram and potassium bromate enhanced by quinine has been elaborated. The eighth chapter describes a simple reversed FIA method for the determination of thiram and nabam fungicides in natural waters with spectrophotometric detection. It is based on the reduction of iron(III) in the presence of thiram/nabam in acidic medium at 60 oC and formation of iron(II)-ferricyanide complex with an absorbance maximum at 790 nm. The method was applied to determine thiram and nabam in water samples using ix Sep-Pak C18 cartridges for solid phase extraction procedure and the results obtained were not significantly different compared with a reported HPLC method. The ninth chapter describes another spectrophotometric method in conjunction with FIA technique for the quantitative analysis of 1-Napthylthiourea (antu). The reaction is based on the alkaline hydrolysis of antu to 1-naphthylamine at 30 C, coupled with diazotized sulphanilic acid, resulting in 4-(sulphophenylazo)-1-naphthylamine and was monitored at 495 nm. The analysis of antu in spiked water samples was extracted using Sep-Pak C18 cartridges. There was no significant difference between the proposed method and a reported HPLC method by applying F-test and paired Student t-test at 95% confidence level. In the tenth and final chapter, general conclusions and future trends are described followed by references, list of publications and title pages of articles published.