Type of Document Dissertation Author Howard, Angela L. URN etd-08282003-155343 Title Strategies for the analytical determination of thermally labile sulfur-containing environmental pollutants Degree PhD Department Chemistry Advisory Committee
Advisor Name Title Taylor, Larry T. Committee Chair Anderson, Mark R. Committee Member Bell, Harold M. Committee Member Long, Gary L. Committee Member Merola, Joseph S. Committee Member Keywords
- Extraction (Chemistry)
- Environmental chemistry
- Sulphur compounds
- Pesticides -- Environmental aspects
Date of Defense 1992-12-05 Availability restricted AbstractIncreasing public awareness of toxic moieties in our environment has put pressure on regulatory agencies to improve testing methods so that these harmful agents can be identified and quantitated at lower and lower levels. The main objective of this work was to investigate analytical methodologies that would allow the sensitive, selective determination of pollutants to be routinely possible. Polar, thermally labile sulfur-containing pesticides and pollutants were our focus analytes. This objective was achieved in two ways: 1) the development of supercritical fluid extraction procedures suitable for these compounds and 2) the interface of a sulfur-selective detector to chromatographic techniques appropriate for thermally labile compound analysis.
Supercritical fluids, particularly CO2, have recently been shown to be suitable replacements for traditionally used organic solvents in extraction. However, due to the polarity of the sulfonyl urea herbicides and thiocarbamate insecticides studied, pure CO2 was found to be an ineffective extractant. Polar SF mixtures (2 and 5 % methanol-modified CO2) were investigated as alternative supercritical extraction fluids. Of the modified fluids, only 2% methanol-modified fluid could be used due to post-SFE trapping problems encountered with the 5% modified fluid. The quantitative extraction of two of these herbicides from water at the 50 ppb level was achieved using the former SF. This SF was also used to extract three thiocarbamates from apples at the 2 ppm level.
In order to achieve the second objective, a sulfur-selective gas chromatographic detector, the ozone-based sulfur chemiluminescence detector (SCD), was successfully interfaced to both packed column supercritical fluid chromatography (SFC) and microcolumn high performance liquid chromatography (micro-HPLC). The packed column SFC/SCD system was shown to be compatible with both pure CO2 and methanolmodified CO2 mobile phases with a detector sensitivity (2 pg S/sec.) comparable to that found with capillary SFC/SCD despite the presence of more CO2 , an effective chemiluminescence quenching agent. The equimolar response of this detector to sulfur was shown to be only somewhat affected by the coelution of other organic species and improper analyte combustion conditions. For micro-column HPLC/SCD, the detector was found to be compatible with methanol/water mobile phases. Mobile phase composition, mobile phase flow rate, air flow rate, and hydrogen flow rate were found to affect the detector's sensitivity. The detector's linear dynamic range, response factor, and detection limits were determined to vary as a function of mobile phase composition. Optimum sensitivity (600 fg S/sec.) was achieved with a mobile phase of 40% methano1l60% water mobile phase compositions investigated. The analysis of polyaromatic sulfur-containing hydrocarbons (PASH's), total sulfur in diesel fuel, and sulfonyl urea herbicides was realized with the SFC/SCD system while thiocarbamate pesticides from an apple matrix were examined with the HPLC/SCD system.
Filename Size Approximate Download Time (Hours:Minutes:Seconds)
28.8 Modem 56K Modem ISDN (64 Kb) ISDN (128 Kb) Higher-speed Access howard.pdf 8.99 Mb 00:41:37 00:21:24 00:18:43 00:09:21 00:00:47 LD5655.V856_1992.H689.pdf 20.56 Mb 01:35:11 00:48:57 00:42:50 00:21:25 00:01:49next to an author's name indicates that all files or directories associated with their ETD are accessible from the Virginia Tech campus network only.
If you have questions or technical problems, please Contact DLA.