In the SRI DGA GC, the sample is injected by peristaltic pump through a unique gas extraction loop. The gas extraction loop consists of permeation tubing encapsulated in a trap-heated glass tube. The permeation tubing is plumbed to the sample inlet, the 10-port gas sampling valve and the waste/sample outlet.
When the sample is pumped through the gas extraction loop, the dissolved gases permeate through the membrane into the extraction chamber. Solenoid valves are included for purging the gas extraction loop with helium between runs.
By reconnecting a few tubing lines, the DGA GC can be configured to prepare dissolved gas standards. A Tedlar bag, or other container, filled with gas standard of a known concentration is connected to the standard pump. The standards preparation vessel is filled with sample liquid, such as sea water or waste water. The standard pump bubbles gas standard into the standards preparation vessel, equilibrating the liquid over time to the known concentration. Equlibration takes about one hour.
Solubility of Gases in Water at 1%:
Hydrogen 0.016ppm
Oxygen 0.43ppm
To obtain these chromatograms, the DGA GC standards preparation module was used to create 13ppb hydrogen gas by weight in water: 1% hydrogen gas standard was pumped through water in the standards preparation vessel for a length of time sufficient to achieve equilibration. The water in the standards preparation vessel was then pumped into the gas extraction loop and run as the sample. The TCD quantifies the large oxygen and nitrogen peaks, while the sensitive HID detects hydrogen down to 13ppb.
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