Investigating weathering in light diesel oils using comprehensive two-dimensional gas chromatography–High resolution mass spectrometry and pixel-based analysis: Possibilities and limitations

Abstract

Petroleum-derived fuels are chronically spilled in urbanized areas, affecting the environment and the population’s health. Forensic investigations of oil spills aim to find the responsible source of the spills. Weathering processes (dissolution, evaporation, photo-oxidation and biodegradation) change the chemical composition of the spills and hamper the matching of spill-source pairs, especially for light diesel oils (i.e. n-C9 – n-C20) in which the source diesels can be very similar due to the refining process and only compounds resistant to short- or middle-term weathering are present. In this study, comprehensive two-dimensional gas chromatography – high resolution mass spectrometry (GC × GC – HRMS) and pixel-based analysis were combined for: i) improve the identification of very similar diesel oils, and ii) identify weathering-resistant compounds that can also distinguish samples from different sources. Diesel oils from two sources that have been exposed to different degrees of evaporation, photo-oxidation and biodegradation in a laboratory setup. The study revealed the tentatively identified octanoic acid methyl ester and n-nonaldehyde were more resistance to evaporation than hydrocarbons < n-C15. Furthermore, the hydrocarbons > n-C17 could be used for source-apportionment of all the diesel oils susceptible to evaporation and photo-oxidation, but only pristane and phytane were also more resistant to biodegradation. Naphthenes, bicyclic sesquiterpanes and adamantanes were more resistant to only photo-oxidation and biodegradation. GC × GC – HRMS enhanced the separation of the highly similar naphthenes in the diesel oils; however, the diagnostic power for forensic spill investigations was still similar to 1D GC – HRMS.