Biomarker Analysis
Biomarkers are a group of compounds, primarily hydrocarbons, found in oils, rock, sediment and soil extracts. Biomarkers are sometimes called “molecular fossils” as they retain all or most of the original carbon skeleton of the original natural product. Biomarker molecules are particularly resistant to microbial attack, and as the ratio of the biomarkers to other hydrocarbon components decreases as the oil degrades, they are very useful in determining the source of spilled oil, differentiating oils, and monitoring the degradation and weathering state of oils under a variety of conditions. The distribution pattern of biomarkers generally differs between oils.
Most knowledge of biomarkers and their diagnostic ratios comes from oil geochemistry and a wide variety of biomarkers have been identified as being of use in the characterisation of crude oils and oil fractions. However, although a wide range of biomarkers can be used for correlation, the ones most appropriate to environmental forensics are hopanes (191 m/z), triaromatic steranes (m/z 231), and sesquiterpanes (m/z 123). The isoprenoids pristane and phytane can also be used as biomarkers as well as for age determination, however as the ratio can be affected by many factors it is not used as a major correlation parameter.
- Hopanes – m/z 191
- Hopanes are C27-C35 pentacyclic alkanes and are found in almost all ancient sediments and crude oils and are generally derived from bacteria.
- Triaromatic steranes – m/z 231
- This group of biomarkers are normally found in petrogenic oils such as crude oils but are removed in lube oils and middle distillates during the refining process. By targeting this group of compounds, it is possible to distinguish between refined lube oil and a heavy fuel/bunker fuel.
- Sesquiterpanes – m/z 123
- This group of biomarkers found in the range C13-C17, are useful for correlating lighter petroleum products such as kerosenes and diesels. They are derived from higher plants and resins, essential oils and some bacteria.
- Isoprenoids – pristine and phytane
- Pristane - IP19 and phytane IP20 are branched alkanes which are derived from the chlorophyll molecule under differing conditions, and are ubiquitous in most oil and sediment extracts making them one of the most important biological markers particularly for estimating age.
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