Graduate Thesis Or Dissertation

 

Selective detection for gas chromatography by ultraviolet spectrometry Public Deposited

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  • Spectrometric detection systems for gas chromatography (GC) based on gas phase ultraviolet absorbance and fluorescence measurements have been developed and evaluated in this research. Polynuclear aromatic compounds (PNAs) are selectively detected by these systems. Limits of detection for PNAs range from 4 ng to 90 ng for absorbance determinations, and from 3 ng to 400 ng for fluorescence determinations made at a fixed waveband. The spacial design and optical components have been carefully selected to be compatible with hightemperature gas-phase measurements (ca. 250°C) while preserving the resolution of the chromatographic separation and enhancing the sensitivity of the multimode spectrometric determinations. Vapor-phase determinations of GC eluates are made directly as they leave the GC column in specially designed, heated flow-through detector cells with low volume and dead space. A long pathlength cell of 167 mm was used to enhance the sensitivity of the absorbance measurements. High-temperature, quartz fiber optic bundles transmit light to and from the detector cell, thus thermally isolating optical components. There are two configurations for these GC detection systems, each advantageous for either quantitative or qualitative determinations, respectively. In the first, waveband selection is accomplished via optical filters. These simple and compact systems are particularly suited to precise and sensitive determinations of polynuclear aromatic compounds. The sensitivity and selectivity of the absorbance and fluorescence measurements vary with individual compounds. These differences also provide some qualitative information about eluates. The second detection system configuration provides repetitive UV spectral information of GC eluates. This computer-controlled system scans a modified Czerny- Turner monochromator and can acquire up to two 62-nm spectra of eluates per second. Spectral information thus obtained may be used for identification purposes and to locate unresolved GC eluates. After compounds have been separated and identified, fixed waveband spectrometric data acquired at an absorption maximum may be used to determine concentrations.
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