Characterization of petroleum-based fuels using comprehensive two-dimensional gas chromatography

Date of Completion

January 1998

Keywords

Chemistry, Analytical|Environmental Sciences

Degree

Ph.D.

Abstract

In comprehensive two-dimensional gas chromatography (GC x GC), two capillary columns are connected in series through an interface known as a "thermal modulator." This device transforms effluent from the first capillary column into a series of sharp chemical pulses suitable for high-speed chromatography on the second column.^ A two-level factorial design was performed to determine which modulation variables had a significant effect on modulator efficiency. Of the variables studied, the temperature difference between the modulator and GC oven, the boiling point of the analyte, and the GC column internal diameter produced significant effects on modulator efficiency.^ The thermal and chromatographic performance characteristics of the modulator were investigated. Direct measurements of the capillary column showed exponential temperature changes during modulator passage. Van't Hoff plots produced estimates of the free energy of interaction between the analyte and stationary phase on the modulator that were in good agreement with literature values.^ GC x GC was applied to three separate analyses of petroleum fuels. A quantitative analysis of trace levels of oxygenates and aromatics in groundwater were performed using headspace solid-phase microextraction (SPME) sampling. The oxygenates studied were methyl-tert-butyl ether (MTBE) and ethyl butyl ether (EBE). The aromatics studied were the BTEX compounds, benzene, toluene, ethylbenzene and xylenes. Results yielded method detection limits of 360-630 parts-per-trillion (v/v). GC x GC resolved all oxygenate and BTEX components from all traditional one-dimensional GC coeluters present in standard gasoline samples.^ Quantitation of BTEX and all heavier aromatic compounds in finished gasoline was performed. The target aromatic species were resolved from other compound classes. Structurally related aromatics were grouped in a manner that facilitated identification and integration. Quantitation produced results directly comparable with more complicated standard methods.^ An oil spill source identification case from the U.S. Coast Guard's Marine Safety Laboratories (MSL) was analyzed qualitatively and quantitatively by GC x GC and compared with standard methods employed by MSL. Several classes of components were used in the analysis, including alkanes, cycloalkanes, alkylbenzenes, alkylnaphthalenes and anthracene/phenanthrenes, The GC x GC results matched the spill to the source. ^

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