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Viewed, Most SPME Extractions Are Performed in Aqueous Matrices.11,16 the Organic Solvent Most Likely Acted As an Interference with the Analyte Extraction

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Viewed, Most SPME Extractions Are Performed in Aqueous Matrices.11,16 the Organic Solvent Most Likely Acted As an Interference with the Analyte Extraction A COMPARISON OF COMMON LABORATORY TECHNIQUES FOR THE ANALYSIS OF THIOCARBAMATE PESTICIDES A Thesis Presented to The Graduate Faculty of The University of Akron In Partial Fulfillment of the Requirements for the Degree Master of Science Tammy Schumacher Donohue August, 2012 A COMPARISON OF COMMON LABORATORY TECHNIQUES FOR THE ANALYSIS OF THIOCARBAMATE PESTICIDES Tammy Schumacher Donohue Thesis Approved: Accepted: ________________________________ ________________________________ Advisor Dean of the College Dr. Claire Tessier Dr. Chand Midha ________________________________ ________________________________ Faculty Reader Dean of the Graduate School Dr. Kim C. Calvo Dr. George R. Newkome ________________________________ ________________________________ Department Chair Date Dr. Kim C. Calvo ii ABSTRACT The United States Environmental Protection Agency has devised a set of regulations limiting the use of thiocarbamate pesticides for the health and safety of humans and the environment. These regulations dictate the maximum amount of thiocarbamate compounds that may be released or present in soil, waste, and groundwater. Therefore, it is important to be able to determine their concentration accurately and reproducibly. A study was conducted to determine the best way to identify and quantify six thiocarbamate herbicides using equipment commonly found in industrial laboratories. Three analytical methods were tested: gas chromatography-mass spectrometry, high performance liquid chromatography, and infrared spectroscopy. They were chosen for their common usage, broad application, and operative ability. A comparison of these methods was made to determine the most effective technique for thiocarbamate identification and quantification. iii DEDICATION To my husband, Chris, whose steadfast belief in me never wavered. Thank you for always letting me know you were behind me, no matter what. I love you. And to my Research Advisor, Dr. Claire Tessier, who took me on without any reason to, stayed late every week, and taught me that research could be fun. A very warm and heartfelt thanks to you both. iv ACKNOWLEDGEMENTS There were many people whose support was inestimable to the completion of this thesis. First and foremost I’d like to thank my family for their constant support and encouragement. I would also like to thank Omnova Solutions, Inc. for the generous use of their instrumentation, and for the opportunity to work and learn in such an exceptional environment. Lastly, I would like to thank Dr. Michael Dunphy of Walsh University. v TABLE OF CONTENTS Page LIST OF TABLES …………………………………………………………….. vii LIST OF FIGURE …………………………...………………………………… viii CHAPTER I. INTRODUCTION TO THIOCARBAMATES …………………………….. 1 II. EXPERIMENTAL ……………………………………………………….... 19 2.1. Materials …………………………………………………………. 19 2.2. Solutions …………………………………………………………. 20 2.3. GCMS Liquid Injection ………………………………………….. 22 2.4. GCMS SPME ……………………………………………………. 24 2.5. HPLC …………………………………………………………….. 28 2.6. IR …………………………………………………………………. 30 III. RESULTS AND DISCUSSION ………………………………………….. 32 3.1. GCMS Liquid Injection .………………………………...………. 32 3.2. GCMS – SPME ………………………………………………….. 40 3.3. HPLC ……………………………………………………………. 52 3.4. IR ……………………………………………………………….. 61 IV. CONCLUSIONS ………………………………………………………….. 65 REFERENCES ……………………………………………………………… 67 vi APPENDIX ......................................................................................................... 70 vii LIST OF TABLES Table Page 1.1 The six thiocarbamate pesticides of interest with their common and scientific names as well as their molecular structures …………….. 4 1.2 Supelco® fiber recommendations based on analyte characteristics ….... 13 2.1 Material Descriptions ………………………………………………….. 20 2.2 Concentrations of the multiple solutions used for this experiment ……. 22 2.3 Temperature program for GC-MS pesticide separation by liquid injection ………………………………………………………… 23 2.4 Temperature program used for SPME optimization testing ………….... 24 2.5 Comparison of fibers examined ……………………………………...… 26 2.6 Solvent gradient for HPLC separation of thiocarbamate pesticides ….... 29 2.7 Isocratic HPLC parameters tested …………………………………….... 29 3.1 Calibration Curve Fittings …………………………………………….... 37 3.2 Limits of Detection for GC-MS by liquid injection ………………….... 38 3.3 GC-MS Limits of Detection and Quantification by liquid injection in parts per million ………………………………………………….….. 40 3.4 Linear correlation coefficient values for SPME pesticide calibration curves ……………………………………………………… 51 3.5 Method detection capabilities for SPME-GC/MS ……..……………… 52 3.6 Average Correlation Coefficient Values for Thiocarbamate Pesticide HPLC Calibration Curves created using Solvent Gradient 1 ... 57 3.7 HPLC background response as determined by Blank Averaging ........... 58 viii 3.8 Limits of Detection and Quantification for the six thiocarbamate pesticides by HPLC ................................................................................. 58 ix LIST OF FIGURES Figure Page 1.1 Molecular structure of carbamate pesticides …………………….…….. 2 1.2 A comparison of the molecular structures of the three types of thiocarbamates ………………………………………………………. 2 1.3 Functionality of thiocarbamate pesticides as dependent on molecular structure …………………………………………………….. 3 1.4 Diagram of a SPME fiber ……………………………………………… 11 3.1 Separation of the Test Solution using GC-MS Temperature Program 1 (Table 2.3) ……………………………………………………………… 33 3.2 Separation of the Test Solution using GC-MS Temperature Program 2 (Table 2.4) ……………………………………………………………… 33 3.3 Calibration curve for methanol dilutions of the Standard Stock Solution for EPTC ……………………………………………………………….. 34 3.4 Calibration curve for methanol dilutions of the Standard Stock Solution for butylate ……………………………………………………………... 35 3.5 Calibration curve for methanol dilutions of the Standard Stock Solution for vernolate ……………………………………………………………. 35 3.6 Calibration curve for methanol dilutions of the Standard Stock Solution for pebulate …………………………………………………………….. 36 3.7 Calibration curve for methanol dilutions of the Standard Stock Solution for molinate ……………………………………………………………. 36 3.8 Calibration curve for methanol dilutions of the Standard Stock Solution for cycloate …………………………………………………………….. 37 x 3.9 Initial SPME GC-MS response using 7 µm PMDS fiber to extract from methanol solvent based pesticide solutions ………………………….... 41 3.10 The effect of multiple extractions from the same vial on analyte peak response …………………………………………………………. 42 3.11 Averaged results of a 2.5% methanol solution containing 1-3 ppm of each pesticide ………………………………………………………. 43 3.12 Effect of sample volume on SPME headspace extraction …………….. 45 3.13 Effects of the addition of sodium chloride to pesticide extraction vials .. 46 3.14 The effect of SPME extraction time on GC-MS peak area response ….. 47 3.15 Effect of agitation speed on pesticide extraction ………………………. 48 3.16 Effect of agitation chamber (extraction) temperature on pesticide extraction ….............................................................................................. 49 3.17 Effect of desorption temperature on peak area response of pesticide chromatograms ……………………………………………………….... 50 3.18 Final SPME calibration curve under optimal extraction conditions …… 51 3.19 HPLC chromatogram of 320 ppm molinate with additional peaks eluted using Solvent Gradient 1 …………………………………………..…… 53 3.20 HPLC calibration curve for molinate using Solvent Gradient 1 ………. 54 3.21 HPLC calibration curve for cycloate using Solvent Gradient 1 ………. 54 3.22 HPLC calibration curve for vernolate using Solvent Gradient 1 ……… 55 3.23 HPLC calibration curve for butylate using Solvent Gradient 1 ………... 55 3.24 HPLC calibration curve for pebulate using Solvent Gradient 1 ……….. 56 3.25 HPLC calibration curve for EPTC using Solvent Gradient 1 …....…..... 56 3.26 HPLC chromatogram of all six thiocarbamate pesticides ........................ 59 3.27 HPLC chromatogrom of all six thiocarbamate pesticides ....................... 60 3.28 HPLC chromatograom of all six thiocarbamate pesticides ..................... 60 xi 3.29 FTIR Spectra of all six Standard Stock Solutions as applied five times to KRS-5 crystals (solvent free, solid state) ............................................ 62 3.30 FTIR spectra of the Standard Stock Solutions of EPTC as applied ten times to a KBr crystal (solvent free, solid state) ............................................... 63 3.31 FTIR Spectra of the Standard Stock solution of EPTC sandwiched between two KBr crystals, ratioed to two clean, blank KBr crystals ..................... 64 xii CHAPTER I INTRODUCTION TO THIOCARBAMATES Thiocarbamates represent a major commercial class of chemical pesticides whose use spans several continents and generates hundreds of millions of dollars in revenue each year.12 Developed during World War II, they have been in mainstream production and use since the 1960’s.13 Thiocarbamates aid in the production of many important crops, including maize and corn, sugarbeets, rice, and soybeans.1 Their success is largely due to their versatile biological significance, and they have been attributed to having hypnotic, analgesic, anesthetic, fungicidal, bactericidal, terbuculostatic, and antiviral properties.4, 5 Thiocarbamates generally serve as graminicides, which are herbicides used to control weedy grasses, and are applied to soil before the emergence of crops.1 Their application is highest in North America and Europe. The term “pesticide” is used in broad application that includes insecticides, herbicides,
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