Date of Award
Doctor of Philosophy
Many improvements in science are contingent on understanding complex multi-component systems. Discovering the identity of components within a sample as well as assaying the amount present is the cornerstone of most scientific research. The separatory power provided by chromatography has led to the embrace of chromatographic methods by virtually every discipline within the physical and biological sciences. The widespread usage of chromatography has led to increasing demand for improved instrumental techniques and detection methods. This dissertation describes three new chromatographic detection techniques which provide improved chromatographic selectivity, sensitivity, and detectability. The first chapter presents a basic introduction to chromatography and describes detection methods in gas and liquid chromatography;The project described in the second chapter is a laser-based absorbance probe utilizing fiber optic technology. The probe is applicable to microbore liquid chromatography, providing a sub-microliter cell volume with a 3-mm pathlength. Linear response is made possible by minimizing stray light. This is accomplished first by reducing reflections through refractive index matching, and second, by using a unique optical delay line and high-frequency modulation, which enables background correction through phase-sensitive detection;Chapter 3 describes a new thermal lens spectrometer suitable for microbore LC detection. A single laser is used and a single beam passes through the cell to simplify alignment. Baseline stability of 1 x 10[superscript]-4 and lock-in detection are made possible by a reference beam and high-frequency modulation (150 kHz). Detectability (S/N = 3) is found to be 3 pg of benzopurpurin 4B at 90 mW excitation (514.5 nm). This corresponds to an absorbance LOD of 4 x 10[superscript]-6 au in a 1-cm cell;In Chapter 4 a new detection method for gas chromatography is described. The response of the ultrasonic gas chromatographic detector is used to determine both the absolute weight and the molar concentration of an unknown analyte without a calibration curve. The method does not require that any physical properties of the analyte be known. A detectability of 1 pg of hexane was found. ftn * This work was performed under contract No. W-7405-Eng-82 with the U.S. Department of Energy.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Kristen J. Skogerboe
Skogerboe, Kristen J., "Improved chromatographic detection methods based on absorbance and ultrasonic measurements " (1987). Retrospective Theses and Dissertations. 8593.