This method is for the collection and analysis of dissolved gases such as methane, ethane and ethylene in ground water. A water sample is collected in a bottle with no headspace. After sample collection, a headspace is generated in the sample by displacing a specific percentage of the water with high purity helium. The bottle is shaken until an equilibrium is established and then the headspace is direct injected onto a gas chromatograph with a thermal conductivity detector (TCD), flame ionization detector (FID) or electron capture detector (ECD).
The concentration of the dissolved gases in the sample is determined by using Henry's law constant (H) for the target analyte, the concentration of the gas in the headspace, the bottle volume, the sample temperature, and the amount of headspace injected.
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| Hold Times, Preservatives, Preps, Collection, Analytical & Documentation | |
|---|---|
| Holding Time: | None specified in the method. |
| Preservatives: | None specified in the method. |
| Required Preps: | 60mL amber glass bottle |
| Collection Method: | Grab sampling |
| Analytical Methodology: | GC/FID |
| Documentation: | 
RSK-175
|
| Analyte | Formula | CAS Number | Detection Limit | |
|---|---|---|---|---|
| Butane | C4H10 |
106-97-8 |
0.03 |
µg/L |
| Propene | C3H6 |
115-07-1 |
0.02 |
µg/L |
| Carbon dioxide | CO2 |
124-38-9 |
400 |
µg/L |
| Methane | CH4 |
74-82-8 |
0.1 |
µg/L |
| Ethane | C2H6 |
74-84-0 |
0.01 |
µg/L |
| Ethylene | C2H4 |
74-85-1 |
0.01 |
µg/L |
| Acetylene | C2H2 |
74-86-2 |
0.03 |
µg/L |
| Propane | C3H8 |
74-98-6 |
0.01 |
µg/L |
| Nitrogen | N2 |
7727-37-9 |
400 |
µg/L |
| Oxygen | O2 |
7782-44-7 |
150 |
µg/L |
* The analytes and detection limits listed for each method represent the typical detection limits and analytes reported for that particular method. Keep in mind that analyte lists may vary from laboratory to laboratory. Detection limits may also vary from lab to lab and are dependent upon the sample size, matrix, and any interferences that may be present in the sample.