Date of Award
Spring 5-7-2019
Track
Chemistry
Degree Type
Thesis
Degree Name
Master of Science in Chemical Sciences (MSCB)
Department
Chemistry
Committee Chair/First Advisor
Huggins Msimanga
Committee Member
Christopher Dockery
Committee Member
Thomas Leeper
Abstract
Pesticides that are used to control pests such as insects, rodents, bacteria, mold, and fungus in food production end up in the fruits and vegetables that we consume. Clearly, concentration levels of pesticides must be carefully monitored. Successful monitoring of the concentrations is critically dependent upon pesticide extraction efficiency, the pesticide structure and the matrix (food product) in which the pesticide is found. Variables such as polarity, solubility, and pH must be investigated. A common approach to develop analysis methods involves spiking food products with pesticides and evaluating method efficiency by calculating percent recoveries from the foods. Sample results from the Georgia Department of Agriculture Labs (Tifton, Ga) showed in some cases, a range of 84% to 140% recoveries for some pesticides on the lower end of ppm concentration levels. These recoveries were obtained from fruit extracts such as peaches, bananas, carrots, and green beans that provided very complex matrices. In this study, recovery range of 95% to 105% is our plausible goal to establish the efficiency of our extraction technique.
We propose to develop a method that will improve percent recoveries by modifying the QuEChERS methods. This proposal entails spiking fruit matrices with known amounts of pesticides and studying percent recoveries by quantifying the extracts with standard instruments like High-performance liquid chromatography-photodiode array (HPLC-PDA), Gas chromatography-mass spectrometer (GC/MS), and Ultra-performance liquid chromatography-ultraviolet (UPLC/UV). The focus will be on improving the extraction process. Starting with eight pesticides, we will study structural differences in the pesticides via middle-infrared spectroscopy to establish extraction compatibility. Also, relative polarities under different pH conditions will be determined using reverse-phase HPLC/UV. This aspect will help with optimizing the organic solvents to be ultimately used for extraction. Lastly, the optimized conditions will be used to analyze bulk pesticides using HPLC-PDA and UPLC-multiwavelength detector (UPLC-MWD) for comparison.
An efficient method was developed by modifying the QuEChERS method using liquid-liquid extraction and the percent recoveries were satisfactory and showed a good precision.