Chemometric Analyses of In Vitro Weathering of a Heavy Fuel Oil

Abstract

Oil spilled into the aquatic environment is susceptible to various types of weathering. Some of these move the compounds, where others degrade them. Overall the weathering processes change the chemical composition of the remaining oil by removing specific compounds. In this thesis the weathering processes evaporation, dissolution, photooxidation and microbial degradation were simulated in vitro. The objective for this was to evaluate the relative chemical compositional changes in the remaining oil as a function of weathering processes. Based on the information of these a model was created, describing effects of natural weathering on a heavy fuel oil. The model was evaluated through analysis of naturally weathered oil samples. The effects of the weathering processes were monitored by gas chromatography – mass spectrometry operating in selected ion monitoring mode. Selected parts of ion chromatograms were preprocessed through a new integrated methodology using correlation optimised warping, which made principal component analysis (PCA) based on chemical patterns of the total ion chromatograms possible. The PCA clearly modelled the individual weathering processes as functions of exposure time, and was validated by separating the long term and short term naturally weathered oil samples. Altogether, the preprocessing methodology was capable of eliminating the concentration effects, optimising signal-to-noise ratios, reducing effects of tailing, presenting chromatographic data across several hundred analyses that were comparable by PCA, and at the same time separate data that possesses high degrees of uncertainty from accurate and useful data.