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USGS CMG Menlo Park Organic Geochemistry Lab--M3267

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Menlo Park:
Main Campus  (  Bldg. 2 - 1st floor Bldg. 2 - 2nd floor Bldg. 15 - 1st floor Bldg. 15 - 3rd floor  )
O'Brien St.  (  1020 O'Brien 1030 O'Brien 1040 O'Brien 1050 O'Brien  )

Room Organic Geochemistry Laboratory
Location Rm. M3267, 3rd floor, Bldg. 15 (McKelvey Bldg.)
Contact Robert J. Rosenbauer
Description Fractionation, and purification of extracted hydrocarbons with silica-alumina gel liquid chromatography into progressively more polar fractions for analysis by gas chromatography and mass spectrometry (GC/MS). Prior to fractionation, dissolved sulfur is removed by treatment with activated copper powder. Additional apparatus is used for the evaporation, concentration, and filtration of each sample.
  1. High capacity and high purity nitrogen generator used to accelerate the evaporation of organic solvents under anoxic conditions.
  2. Six fume hoods to contain organic solvents.
  3. Zymark(tm) TurboVapII 6 position evaporation system.
  4. Twelve position turret for blowdown of small volumes of solvent.
  5. Micro & macro- analytical balances for weighing between .001 mg to 1200 g.

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.

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