Date of Award

6-6-2001

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

First Advisor

David T. Pierce

Abstract

Investigations leading to the determination of petroleum hydrocarbons in water have been driven by the need to monitor components with known or suspected health risks. Compounds such as benzene and toluene, abundant in fuels, are known to be carcinogenic and genotoxic. While the effects fuels have on endocrine systems are still unknown, there is a great concern on the effects of long-term exposure to both humans and animals. Mature laboratory methods exist for the low-level determination of petroleum hydrocarbons. However, these methods require expensive instrumentation. In this project, an inexpensive, readily field portable sensor using a thickness shear mode resonator combined with thin organic films has proved useful for aggregate determinations of light fuels in water. A non-Sauerbrey response, associated with the plasticization of the polymer film, was found to be dependent on the concentration of petroleum hydrocarbons present. Thickness shear mode resonator analysis was performed using 10 MHz quartz crystals with polysiloxane thin films for in situ determination of individual and aggregate petroleum hydrocarbons. Individual resonator responses for BTEX (benzene, toluene, ethylbenzene and xylene isomers) and C6−C 8 aliphatic components were measured with method detection limits found in the low ppm range. Responses were additive indicating that aggregate determinations were feasible. Interferences from sample turbidity and ionic strength were overcome using simple sample preparation methods. Fuel contaminated samples were analyzed with respect to aggregate standards and verified by purge and trap or solid phase microextraction gas chromatography. Aggregate detection limits similar to those of single components were found. Field analysis was performed to demonstrate the instrument's stability and portability. Investigations were also undertaken to better understand the non-Sauerbrey response, which indicates the sensor responds to viscoelastic changes rather than mass changes. Traditionally, sensors responding in this manner have been avoided due to the complex nature of the response. Here, the shear moduli associated with the polymer's viscoelastic properties were determined from impedance data. Films that adhered to a Sauerbrey response displayed loss tangent values that were much lower than 1, while non-Sauerbrey films had loss tangent values equal to or slightly lower than 1.

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