The development of a high spectral-resolution laser-excited molecular fluorescence system and its application to gas chromatography and the determination of polynuclear aromatic hydrocarbons Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/8w32r823d

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  • A high-spectral resolution laser-excited molecular fluorescence system was developed that utilizes a pulsed supersonic expansion to simplify the fluorescence excitation spectra of large, gas-phase aromatic molecules diluted in an excess of a monatomic gas. A microcomputer was used to control and synchronize the instrumental components, which included a Chromatix CMX-4 tunable dye laser, a novel detector/vacuum cell, and a modified automobile fuel injector that was used as the pulsed supersonic nozzle. The spectra of two closely-related, model polynuclear aromatic hydrocarbons (PNAs), fluorene and 1-methylfluorene, were acquired and exhibited spectral bandwidths (FWHM) of 0.1 nm or less, compared to the bandwidths of 5 to 10 nm that are observed in the static gas phase. These high resolution spectra were acquired despite using only a low-volume rotary mechanical pump to maintain the supersonic expansion. The gas-pulse characteristics of the fuel injector were examined to establish proper operation of the valve. In addition, factors such as the type of diluent gas used, and the axial position that the laser intersects the expansion, were examined in terms of their influence on the observed spectra. Helium was determined to be the best diluent gas for this system since the use of argon resulted in the production of significant PNA-Ar clusters. The laser-excited fluorescence system was then interfaced to a packed-column gas chromatograph, which provides both a means of quantitative sample introduction, and the additional selectivity required for the analysis of very complex mixtures. A theoretical model was developed to describe the interaction between the GC mass flow, which is continuous, and the mass flow through the supersonic nozzle, which is pulsed in nature. Fluorescence excitation chromatograms were acquired by monitoring the eluate fluorescence signal at a transition wavelength characteristic of one of the model compounds. A calibration curve was constructed for 1-methylfluorene, and was used to calculate a detection limit of 6 ng. In addition, the excellent selectivity provided by the system was demonstrated by acquiring fluorescence-excitation chromatograms of mixtures containing the two model compounds, using different excitation wavelengths. Finally, the requirements for performing internal standard quantitation with highly selective detectors such as this are discussed. A versatile, programmed-excitation-wavelength scanning method was then developed that allows multiple PNA analytes to be detected in a single chromatographic elution. Relative response factors calculated for fluorene and 1-methylfluorene from replicate chromatograms, were shown to be reproducible, thereby allowing internal standard quantitation to be performed using this detection system.
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  • description.provenance : Approved for entry into archive by Patricia Black(patricia.black@oregonstate.edu) on 2013-05-30T15:51:07Z (GMT) No. of bitstreams: 1 HeinScottJ1989.pdf: 3016294 bytes, checksum: 64e3d10fa3455278151c5cc2387eeac9 (MD5)
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