Date of Award

4-1-1995

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

Abstract

Part I. Laser Raman gas diagnostics have been used extensively in combustion furnaces and hydrocarbon flames to probe basic combustion products. Raman spectroscopy presents itself as being a useful analytical technique for these hostile environments because it is sensitive yet non-intrusive. The topic of this research is on the application of Raman spectroscopy to element-specific detection. The non-metals (e.g. C, N, O, etc.) are detected via the Raman scattered radiation from their combustion products in a H$\sb2$/Air flame.This study will present the analytical application of high temperature Raman spectroscopy to the detection of non-metal compounds via the Raman scattered radiation from the combustion products. In addition, a discussion of the major emission bands, the linear dynamic range, and the detection limits of various non-metals will be outlined.Part II. A laser light-scattering detector (LSD) has been developed for gas chromatography which has sensitivity to alcohols. The LSD consists of a miniature concentric nebulizer which uses a cold atomization gas and an argon-ion laser. Calibration curves for the alcohols were found to be sigmoidal-shaped, as expected. Signal-to-noise ratios were optimized by examining the photomultiplier tube temperature, collection wavelength, and detection scheme (i.e., photon counting vs direct current detection). Limits of detection for the five test alcohols studied were in the 2-8 $\mu$g/second range.Part III. Environmentally-important compounds in groundwater (e.g., BTEX) have been isolated and preconcentrated from their water matrix via solid-phase microextraction (SPME) and then determined by gas chromatographic (GC) techniques. To date, however, there have been no applications of SPME which employ spontaneous Raman spectroscopy as an in-situ detector. Raman spectroscopy offers several advantages over GC detection for SPME including remote-sensing via fiber optics and real-time observations.The topic of this research is the application of Raman spectroscopic detection to SPME for the determination of aromatic compounds in water. A small bead (D = 5.0 mm) of OV-1 stationary phase serves as the solid-phase extraction medium. Following extraction, the OV-1 bead is spectroscopically probed by a conventional Raman spectrometer.The analytical applications are shown by the determination of benzene, o, m, and p-xylene, ethylbenzene and toluene in water samples. The detection limits for these compounds are in the range of 1-4 ppm and linear dynamic ranges are between 10-50. It will be shown that SPME greatly enhances the detection limit versus a non-extracted analyte (between 2-3 orders of magnitude enhancement). In addition, the application of fiber optics to the detection system will be discussed.

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