Development of analytical protocols for rapid and sensitive analysis of herbicide residues with flow-gated capillary electrophoresis
Capillary electrophoresis (CE) has become an important technique for the separation and detection of ionic species due to the advantages it carries, including high separation efficiency, reduced consumption of reagents and samples, and rapid analysis. However, preconcentration methods are often required in CE when it comes to detecting trace levels of analytes due to its low sample injection volume and short optical pathlength. The goal of my research projects was to develop efficient and robust preconcentration techniques for sensitive detection of herbicide residues in environmental and food samples via flow-gated CE. This dissertation first presents a simple and robust preconcentration technique: field-amplified sample injection (FASI) coupled with electrokinetic supercharging (EKS). It was successfully applied to the sensitive detection of herbicide residues in surface water systems with flow-gated CE, and it improved the detection sensitivity of glyphosate (GlyP) by 861 times with high accuracy and precision. Then, FASIEKS technique was studied comprehensively using various combinations of the electropherograms of FL and 5-FAM, fluorescence imaging, and computer simulations. As a result, two kinds of EKS processes were studied: two-step EKS and simultaneous EKS. The twostep EKS method was applied to the detection of GlyP residues in cereal samples. Lastly, the extraction efficiency of commercial molecularly imprinted polymer (MIP) cartridges for GlyP and aminomethylphosphonic acid (AMPA) was tested. GlyP and AMPA got 84% and 70% recovery, respectively. In addition, we found that the cartridge had excellent desalting ability: the conductivity of water samples from Arkansas river was reduced by 99.9% after the SPE via the MIP cartridge. The cartridge can be used for desalting where salts often generate adverse effects on the detection sensitivity and accuracy.
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