TDI-Brooks International - Scientific Services On A Global Basis

Headspace Gas Analysis refers to the determination of interstitial light hydrocarbon gases including methane, ethene, ethane, propene, propane, butenes, iso-butane, n-butane, neo-pentane, iso-pentane, and n-pentane (C1-C5) by Gas Chromatography/Flame Ionization Detection (GC/FID).

The natural presence of high levels of C2+ alkane gases serves as a good indicator of migrating thermally-sourced gas, because ethane, propane, the butanes, and the pentanes are not microbially produced at high levels in marine sediments. The light hydrocarbon gases are not very soluble in water, so they can be extracted from a sediment and water sample into a gas such as nitrogen by a partitioning procedure.

Sediment samples are canned immediately after piston core retrieval for headspace gas determinations. Sediment sections are immediately extruded from the core barrel’s liner into cans containing poisoned, hydrocarbon-free seawater. The cans are sealed after flushing the headspace with purified nitrogen, then frozen.

In the laboratory, the cans are thawed and kept at 40 deg C for at least 4 hours. The light hydrocarbons dissolved in the interstitial water are equilibrated with the nitrogen gas phase at that temperature by vigorous agitation with a high-speed shaker.

Prior to the analysis of samples, a calibration curve is established for each analyte to determine the sensitivity and confirm the linear range of the GC/FID system.

TDI-Brooks has developed a unique headspace gas can auto-sampler which allows for around-the-clock analysis with excellent accuracy and data reproducibility. Each autosampler batch analyzed includes samples, method blanks, and duplicates.

The computer software automatically integrates analyte peaks based on their retention times and analysts visually confirm that each analyte peak is integrated correctly by the software.