Spillers beware: Some oil-spill investigations may one day involve a different and perhaps better kind of chemical fingerprinting, if investigators pick up on and decide to use research done at Environment Canada.
The work shows that one particular family of molecules, bicyclic sesquiterpanes, may be better suited to identifying some oils and some refined products than families currently in use
The research group involved in the work, which is outlined in a recent issue of <em>Journal of Chromatography A</em>, is based at Environment Canada's Emergencies Science and Technology Section.
According to the EC researchers, the families of molecules currently used to distinguish between one oil and another include pentacyclic triterpanes, regular and rearranged steranes, and mono-aromatic and tri-aromatic steranes in the residual oil range. However, because of their high boiling points, the triterpanes and steranes tend to be present in very low concentrations in lighter petroleum products such as jet fuels and mid-range diesels. Or worse, they can be absent altogether.
Bicyclic sesquiterpanes are bicyclic alkanes with various combinations of methyl and ethyl groups attaching to the two carbon rings, which puts the molecules in the C14 to C16 range.
In work they describe as one of the first attempts to carefully quantify sesquiterpanes in samples, the EC researchers found that bicyclic sesquiterpanes occurred in significant concentrations in all of the 14 crude oils they observed. Typical concentrations were around 1,000 to 3,000 micrograms of sesquiterpanes per gram of sample. As for the refined products they studied, the researchers found most mid-range fuels contained a total of 4,000 to 8,700 micrograms per gram, while heavy residual fuels had 255 to 2,000 micrograms per gram. As they had anticipated, there were little or no sesquiterpanes detectable in very light and very heavy fractions: gasoline, light kerosene and heavy-end lubricating oils.
Another useful attribute they found in the family of sesquiterpanes was that different crudes and different petroleum products had distinctive sesquiterpane profiles. This was true in terms of the absolute concentrations of each molecule present in samples and in terms of the proportions of each molecule relative to the rest of the sequiterpanes present.
And as crude and diesel samples weathered, these molecules remained quite stable chemically, which meant diagnostic ratios remained stable too.
The EC researchers told The Barrel that among folk who might benefit from using bicyclic sesquiterpanes were environmental scientists who do oil-spill characterizations, identification studies, and environmental forensics, particularly when working with mid-range diesel fuels that don't contain the traditionally-used diagnostic molecules.
They added that bicyclic sesquiterpanes were no panacea. Rather, scientists should use "a multi-criteria approach to characterize unknown spilled oil [to] identify its source."
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