Application of stir bar sorptive extraction thermal desorption gas chromatography mass spectrometry for the study of water accommodated fractions of fossil fuels and biodiesel.

摘要

Even though measures are taken to decrease accidental release of crude oil and refined fuels into the aquatic environment, continued demand of such fuels---particularly in the transportation sector---pose a continued threat to the aquatic environment throughout their handling, processing, and consumption. Even though measures can be taken to remove the visible layers of fuel in water, it has been shown that constituents of these fuels---that partition into water---can have adverse health effects on the aquatic organisms at low concentrations that are not necessarily predictable through the study of the actual fuel's original composition. Consequently, this renders the need for an extraction method that can quickly and efficiently extract these constituents from various types of water matrices so that the impact of fuels on aquatic life and the integrity of the environment can be studied and monitored in an accurate and timely manner.;The overarching goal of this project was to develop a less time consuming, effective and, environmentally friendly method to assess the composition of water accommodated fractions of refined fuel products. Diesel, having a wide variety of hydrocarbons, and its more environmentally friendly alternative biodiesel (B100) were selected for this study. More specifically, the study was aimed to: (1) optimize the stir bar sorptive extraction (SBSE) method before subsequent thermal desorption-gas chromatography mass spectrometry (TD-GCMS) to extract and analyze biodiesel fatty acid methyl esters (FAMEs) and dominant diesel hydrocarbons, by varying organic solvent addition in SBSE extraction, the stir time, and pH adjustment; (2) compare the composition between the fuel and its water accommodated fraction (WAF); and (3) implement the optimized parameters on actual water samples. Water samples were collected from Long Beach, California and the Gulf of Mexico.;Methanol was chosen as the organic solvent for the SBSE optimization. Our study found that methanol percentages of 50 percent---for n-alkanes---and 30 percent for aromatic hydrocarbons---in diesel rendered the better extraction efficiency from water matrices. For biodiesel, by 40 percent methanol content, FAMEs were sufficiently extracted. For all compounds of all fuels 4 hours rendered the best extraction efficiency for all fuels as a whole.. Our result showed that no pH adjustment was deemed necessary for improving the extraction recovery of water accommodated fraction of fuels. The water accommodated fraction of diesel showed an increased presence of aromatic hydrocarbons when compared to their presence in the diesel pure source in comparison to aliphatic hydrocarbons. Using biofuel (B100) the water accommodated fraction stayed relatively the same between saturated and unsaturated FAMEs. The detection limit of the optimized method was estimated to as low as 5ng/L for selected diesel alkanes, 5ug/L for selected diesel aromatic hydrocarbons, 5ppt for saturated hydrocarbons, and 0.1ug/L for unsaturated FAMEs. Using the optimized methanol and stir time parameters, water samples from the Gulf coast and the shores of Long Beach, CA were found to contain non-detectable or non-quantifiable levels of diesel constituents.;Results from this study will allow us to potentially analyze the toxicity and degradation of WAFs of diesel and similar fuels in fresh and sea water samples in an efficient and more environmentally conscious manner. Future directions in this research should be aimed towards further implementing this technique and its optimized parameters on actual water samples containing oil and to validate the method before fully applying this technique over other commonly used extraction techniques for the analysis of fuels.