Most of these geologic investigations begin with the acquisition and preservation of a carefully considered geologic sample of gas, liquid, or solid.
Geochemical analyses can then provide insight into the composition, structure, properties, and reactions of this matter, especially its atomic and molecular structure.
Organic geochemistry focuses on a particular subset of compounds containing carbon-carbon bonds that form the building blocks of their molecular framework.
A particularly useful group of these compounds are biological markers or biomarkers.
These are complex organic compounds, or groups of compounds, composed mostly of carbon and hydrogen and occasionally, some other elements.
They are actually "molecular fossils" derived from formerly living organisms.
These compounds, commonly found in rocks and sediments, persist relatively unchanged in structure from their parent organic molecules, for a long time in the environment.
Due to their refractory nature and complex structure, biomarkers are useful tools for the geochemist to determine the origin and to differentiate sources of geologic materials.
For example, biomarkers can be used to determine the extent of marine versus terrigenous input into sediments or the nature and amount of other anthropogenic contamination in the environment.
Biomarkers can also be used to correlate sources of hydrocarbons and thus differentiate between natural and pollutant hydrocarbon residues that are often found along coastlines.
Biomarkers are analyzed by
gas chromatography and mass spectroscopy (GC/MS) after solvent extraction of a sediment, tar, or oil mixture and then liquid chromatography to separate and purify the compounds of interest.
Our laboratory has state-of-the-art microwave extraction and solvent reduction systems and an automated GC/MS.
Normally, biomarkers are determined by ratios of compounds based on their mass spectral response.
Presently, quantitation is performed mainly by the use of external standards, although calibration procedures are in place to use internal standards and surrogates to more accurately calculate absolute concentrations of selected compounds.