University of Bristol EARTH SCIENCES

Sounds complicated and in fact it is! But we can break down the science into something we can understand.

This technique allows use to gain information from non-mineralised remains. The two main ways in which "soft" parts may be preserved are:

1. Authigenic mineralisation-replacement by a variety of minerals.

2. Survival of the original material.

We use Py-GC/MS as an analytical tool to help us identify organic compounds, especially in fossils. The technique essentially starts by separating the macromolecules ( by flash-pyrolysis) and using the results from the gas chromatography we are able to identify individual molecules through mass spectrometry. We are then able to identify the original organic compounds.

But how is this done? All compounds possess volatility to a greater or lesser degree (a tendency to boil and change to a gas). This makes GC/MS a suitable technique only on the less stable molecules ( stable molecules tend not to be as volatile). Pyrolysis breaks the bonds by heating the compounds of a sample ( within an inert atmosphere) to a temperature of 610C for 10 seconds. This fragments the molecular structure to a number of smaller compounds.

The compounds are swept directly into the gas chromatograph in a flow of helium gas. The compounds are then heated in a thermostated oven, the temperature is then gradually increased. This leads to vaporisation of the various compounds, which are then swept along to the detector end of the analyser. The various compounds arrive at different times based on their boiling points (volatility), those compounds with lower vapour pressures ( higher boiling points) take longer to emerge at the detector. At the detector end they are measured, identified and recorded.

Combining gas chromatography with mass spectrometry provides us with a powerful and reliable analytical tool. A comprehensive data base of molecular compounds is held at the University of Bristol. This allows us to examine individual molecules and this enables us to reconstruct the original compounds and identify the original organic structure.