Date of Award
Doctor of Philosophy (PhD)
Isiah M. Warner
The analytical investigation of the natural insecticide pyrethrum has been conducted. In this research, novel approaches were designed to yield either faster, or more complete separation of the active pesticidal esters in pyrethrum extracts as well as more complete conformational information of the structures of these compounds in solution. A combination of techniques was used: micellar electrokinetic chromatography (MEKC), nuclear magnetic resonance spectroscopy (NMR), and capillary electrochromatography (CEC). Using MEKC, an optimized separation of the six pyrethrin esters was achieved in 25 minutes with 25 mM Tris, buffered at pH 9, containing 30 mM SDS, 25% (v/v) acetonitrile, and an equal volume ratio of acetonitrile/water sample matrix at a voltage of 25 kV. The use of 0.5% (w/v) poly-SUS enhanced resolution of the pyrethrin esters and shortened the total analysis time from 25 to 20 minutes, compared to the SDS mediated separation. The optimized MEKC results are compared to the HPLC separation of these esters and show an improvement in efficiency and total analysis time. In order to deduce structural information about the natural forms of the pyrethrin esters in solution, both 1D and 2D NMR data was correlated with Molecular Modeling calculations. The results indicated that both pyrethrin I and II adopt a "chair" conformation in chloroform solution. Additionally, the new separation technique of capillary electrochromatography (CEC) was used to develop novel strategies to separate both pyrethrin and the tocopherol isomers of vitamin E. CEC shows much promise due to its ability to separate similar compounds with high efficiency and short run times. In order to expand the use of the chiral polymeric micelles, used by our laboratory to achieve chiral separations, stationary phases for use in LC and CEC were designed with the monomer and polymeric micelle of sodium N-undecenoyl-L, L leucyl-valinate (SULV).
Henry, Charles William III, "Development of Novel Separation Strategies: Part I. The Separation and Characterization of the Insecticidal Pyrethrin Esters. Part II. Separations in Capillary Electrochromatography." (2000). LSU Historical Dissertations and Theses. 7364.