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Gulf Coast Repository

Gas Chromatographs (GC)

Overview

Thumbnail image of Gas Chromatograph The gas chromatographs are configured for measuring hydrocarbons (C1-C7) along with oxygen and nitrogen. The instrument makes use of a flame ionization detector (FID) for the hydrocarbons and a thermal conductivity detector (TCD) for oxygen, nitrogen, methane and carbon dioxide.

Instrument Make & Model

Agilent 7890

Estimated Measurement Time

  • Sample Measurement: ~30–60 minutes per sample

Quantity of Sample Material

5 mL of headspace gas per sample

Principles & Analytical Capabilities

The GC makes use of 4 switching valves to direct and control flow through 4 columns and then into 2 detectors. Injected sample flushes and fills 2 sample loops with an exit path to vent. On run start, valve switches direct the sample in the sample loops in 2 separate paths. The FID flow path sends samples through a DB-1 and AL/S column on the way to the FID. The TCD flow path sends samples through a PLOT/Q+PT and MoleSieve column on the way to the TCD.

Data Generated

Data components:

  • Methane (CH4)
  • Ethene (C2H4)
  • Ethane (C2H6)
  • Propene (C3H6)
  • Popane (C3H8)
  • n-Butane (C4H10)
  • iso-Butane (CH3-C3H7)
  • n-Pentane (C5H12)
  • iso-Pentane (CH3-C4H9)
  • n-Hexane (C6H14)
  • iso-Hexane (CH3-C5H11)
  • n-Heptane (C7H16)
  • iso-Heptane (CH3-C6H13)
  • Nitrogen (N2)
  • Oxygen (O2)
  • Carbon dioxide (CO2)

Data files:

  • Concentration results (CSV): tabular file of hydrocarbon, O, CO2 concentrations

Raw files:

  • Chromatograms (PDF): instrument software generated report including chromatograms and peak areas

Data Example

Graph of headspace gas measurements of methane, ethane, ethene, propane, iso-butane, and iso-pentane from Hole U1610A.
Headspace gas measurements of methane, ethane, ethene, propane, iso-butane, and iso-pentane from Hole U1610A of IODP Expedition 401 in the Gulf of Cádiz. 1

Procedures & Manuals

References

1  Flecker, R., Ducassou, E., Williams, T., Amarathunga, U., Balestra, B., Berke, M. A., Blättler, C. L., Chin, S., Das, M., Egawa, K., Fabregas, N., Feakins, S. J., George, S. C., Hernández-Molina, F. J., Krijgsman, W., Li, Z., Liu, J., Noto, D., Raad, F., … Yousfi, M. Z. (2025). IODP Expedition 401 Gas safety report [Data set]. International Ocean Discovery Program. https://doi.org/10.5281/zenodo.16423718