We then place the bitumen at the top of an open silica column (as shown above). By eluting the column (sending the solvents through the column) with different organic solvents, three groups of compounds which are present in all bitumen are separated (in order of elution):
- n-alkanes (also known as saturates or paraffins)
- aromatic hydrocarbons
- polar compounds
Aromatic rings (left) and n-alkanes (right), with no double bonds
N-alkanes (or normal) have no double bonds, like the long chain shown above. That is, all their bonds are saturated, hence the name saturates. We are particularly interested in this group of compounds studying biomarkers, as during diagenesis, double bonds degrade into single bonds. The molecular fossils that we seek in rocks, then, are saturated, and have only single bonds. Aromatics have the characteristic aromatic ring, a 6-ring carbon with three double bonds, like the ring shown above.
We then attempt to identify the specific compounds present in the saturate fraction using gas chromatography – mass spectrometry.