Investigation into the quantitative aspects of supercritical fluids as mobile phases for chromatography and extraction

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Virginia Tech


Supercritical fluids were introduced as mobile phases for chromatography and extractions in the early sixties. Over the past decade the technique has received increased attention, largely owing to the introduction of several commercial instruments and to the ease of adapting available commercial equipment for use in sfe and sfc. This dissertation examines the use of supercritical CO₂ as a mobile phase for chromatography and extraction. The first chapter explores the problems and provides background for the research. The physical properties of supercritical fluids are described and pertinent recent research is identified and summarized. The following chapter presents the design of three interrelated studies that investigate in-situ concentration, quantitative aspects of sfc, and quantitative aspects of sfe. The first of the three studies examined the exploitation of the innate properties of a supercritical fluid. Because the mechanism of elution with supercritical fluid mobile phases is based on solvation, it was possible in this study to concentrate analytes at the head of the supercritical zone. Concentration was followed by supercritical fluid chromatography. This allowed the analysis of sample components at part per billion levels. The use of supercritical fluids as mobile phases for chromatography and the quantitative nature of sfc with flame ionization detection was examined in the second study. Under numerous detector and injector configurations, a distinct decrease in response factors with an increase in carbon number was evident.

Results showed that the decrease in response factors was related to an increase in CO₂ flow through the detector. The magnitude of the decrease was multivariably dependent.

The third study dealt with the quantitative aspects of using a supercritical Oobile phase for the extraction of PNAs and pesticides from several matrices including contaminated soil. Results showed that sfe is a reliable, easy, and efficient (> 85% recovery) method of removing trace materials from contaminated soil. Implementation of a simple resistively heated collector was used to circumvent the problems of extracting damp matrices such as soil. The results and conclusions are presented in the final two chapters.