Micro-Extraction and Detection/Quantification of Trace Pesticides in Various Matrices
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Micro-extraction and detection/quantification of trace pesticides in various matrices by JOSEPH MOSOTHO GEORGE THESIS Submitted in fulfilment of the requirements for the degree DOCTOR OF PHILOSOPHY in CHEMISTRY in the FACULTY OF SCIENCE of the UNIVERSITY OF JOHANNESBURG Supervisor: Prof DBG Williams Co-supervisor: Dr L Marjanovic June 2012 AFFIDAVIT: MASTER’S AND DOCTORAL STUDENTS TO WHOM IT MAY CONCERN This serves to confirm that I______________________________________________________ Full Name(s) and Surname ID Number____________________________________________________________________ Student number__________________________________________________ enrolled for the Qualification___________________________________________________________________ Faculty of Science______________________________________________________________ Herewith declare that my academic work is in line with the Plagiarism Policy of the University of Johannesburg which I am familiar. I further declare that the work presented in the ___________________________________(minor dissertation/dissertation/thesis) is authentic and original unless clearly indicated otherwise and in such instances full reference to the source is acknowledged and I do not pretend to receive any credit for such acknowledged quotations, and that there is no copyright infringement in my work. I declare that no unethical research practices were used or material gained through dishonesty. I understand that plagiarism is a serious offence and that should I contravene the Plagiarism Policy notwithstanding signing this affidavit, I may be found guilty of a serious criminal offence (perjury) that would amongst other consequences compel the UJ to inform all other tertiary institutions of the offence and to issue a corresponding certificate of reprehensible academic conduct to whomever request such a certificate from the institution. Signed at Johannesburg________________ on this _______ of ____________________2012 Signature__________________________________ Print name_________________________ STAMP COMMISSIONER OF OATHS Affidavit certified by a Commissioner of Oaths This affidavit conforms with the requirements of the JUSTICES OF THE PEACE AND COMMISSIONERS OF OATHS ACT 16 OF 1963 and the applicable Regulations published in the GG GNR 1258 of 21 July 1972; GN 903 of 10 July 1998; GN 109 of 2 February 2001 as amended. i Table of Contents List of Figures..................................................................................................................... viii List of Tables ...................................................................................................................... xiii Acknowledgements ............................................................................................................ xv List of abbreviations .......................................................................................................... xvi Synopsis ............................................................................................................................. xix Chapter 1: Introduction and literature review ..................................................................... 1 1.1 Introduction to the thesis ............................................................................................... 1 1.2 Applications of chemicals, their fate and social aspects in everyday life ........................ 2 1.2.1 Applications of chemicals in agriculture .................................................................... 2 1.2.2 Fate of pesticides in plants or the environment and their effects thereon ................ 3 1.2.3 Effects of pesticides on human health ...................................................................... 3 1.2.4 Legal, political and social aspects of pesticide use and misuse .................................. 4 1.3 Analysis of pesticides and other organic compounds ..................................................... 5 1.3.1 Analytical method development and validation ........................................................ 6 1.3.2 Chromatographic methods of analysis ...................................................................... 8 1.3.2.1 Column chromatography ................................................................................... 8 1.3.2.2 Gas chromatography.......................................................................................... 9 1.3.3 Detectors for chromatography ............................................................................... 10 1.3.3.1 Mass spectrometry as a detector for chromatographic analysis ....................... 12 1.3.4 Hyphenated/coupled instrumental methods .......................................................... 12 1.3.4.1 Hyphenation of HPLC and MS .......................................................................... 13 1.3.4.2 Hyphenation of GC with MS ............................................................................. 13 1.3.5 Quantitative analysis in chromatography ................................................................ 14 1.3.6 Recent developments in chromatography .............................................................. 15 1.4 Sample preparation techniques for chromatography analysis ..................................... 16 1.4.1 Liquid-based sample preparation techniques ......................................................... 17 1.4.1.1 Soxhlet extraction ............................................................................................ 17 1.4.1.2 Supercritical extraction techniques .................................................................. 18 ii 1.4.1.3 Solvent micro-extraction .................................................................................. 20 1.4.2 Solid-based sample preparation techniques ........................................................... 25 1.4.2.1 Solid-phase extraction (SPE)............................................................................. 25 1.4.2.2 Solid-phase micro-extraction SPME ................................................................. 27 1.4.3 Dispersive methods ................................................................................................ 28 1.4.3.1 Dispersive solvent micro-extraction ................................................................. 28 1.4.3.2 Dispersive solid-phase extraction (D-SPE) ........................................................ 29 1.4.4 Sample preparation involving chemical reactions ................................................... 30 1.4.4.1 Derivatisation-coupled sampling ...................................................................... 30 1.4.4.2 Chelation and complex formation .................................................................... 32 1.5 Mass-transfer in solvent microextraction ..................................................................... 33 1.6 Objectives of the study ................................................................................................. 35 1.7 References .................................................................................................................... 37 Chapter 2: Application of the bubble-in-drop single drop micro-extraction (BID-SDME) method for monitoring of herbicides from farm areas .............. 47 2.1 Introduction .................................................................................................................. 47 2.2 Experimental ................................................................................................................ 49 2.2.1 Reagents and chemicals .......................................................................................... 49 2.2.2 Standard solutions .................................................................................................. 49 2.2.3 Preparation of soil samples ..................................................................................... 50 2.2.4 Instrumentation ..................................................................................................... 50 2.2.5 Micro-extraction procedure .................................................................................... 51 2.2.6 Performance of the analytical method for metolachlor .......................................... 51 2.2.7 Sampling of the soil samples ................................................................................... 51 2.2.8 Evaluation of extraction recovery ........................................................................... 52 2.3 Results and discussions ................................................................................................ 52 2.3.1 Development and validation of BID-SDME method for triazines analysis ................ 53 2.3.2 Validation of the BID-SDME method for accuracy using atraton ............................. 55 iii 2.3.3 Validation of the BID-SDME method for reproducibility .......................................... 57 2. 4 Application of the BID-SDME method in the analysis of metolachlor and atrazine in agricultural soil samples ..................................................................................................... 59 2.4.1 Extraction and analysis for monitoring of metolachlor and atrazine from farm soil. 59 2.4.2 Extraction efficiency of metolachlor using BID-SDME.............................................. 62 2.4.3 Linear dynamic range and detection limits for metolachlor .................................... 62 2.4.4 Application of the BID-SDME method in monitoring