addressing uncertainty in oil and natural gas industry greenhouse

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A molecular sieve PLOT column is used for the separation of the permanent gases helium (He),
hydrogen (H 2 ), oxygen (O 2 ), nitrogen (N 2 ), and methane (CH 4 ).
A thick film WCOT2) column coated with an apolar phase is used for the separation of the C3 to C8
(and heavier) hydrocarbons.
The permanent gases helium (He), hydrogen (H 2 ), oxygen (O 2 ), nitrogen (N 2 ), and methane (CH 4 ) are
detected with a thermal conductivity detector (TCD). The C2 to C8 hydrocarbons are detected with a flame
ionization detector (FID).
For the analysis of natural gas substitutes, carbon monoxide (CO) and carbon dioxide (CO 2 ) are detected
using an FID after reduction of the components to CH 4 by a methanizer. Use of a methanizer makes it
possible to detect CO and CO 2 at mole fractions greater than 0,001%. If the samples do not include CO or
CO 2 , or if the CO and/or the CO 2 mole fraction exceeds 0,02%, a methanizer is not required. CO and CO 2
may then alternatively be detected with the TCD.
When analyzing natural gas substitutes, the PLOT column described in 3.1 can also be used for the
separation of ethyne (C 2 H 2 ) and ethene (C 2 H 4 ) and the molecular sieve PLOT column can also be used for
the analysis of carbon monoxide (CO).
Typical precision values for this method are provided in Table A.1 of the standard. These values have been
obtained from practical experience and give an indication of the performance of the method. As such, they
cannot be compared with precision values mentioned in informative annexes of other parts of ISO 6974, as
they are very much dependent on the quality of the calibration gases used and the laboratory skills.
For specifies concentrations < 1.0 mole%, the relative repeatability and reproducibility is expected to be 2
and 4%, respectively. For higher concentrations, ranging from 1-50 mole%, the relative repeatability and
reproducibility are around 0.8 and 1.6% respectively.
e. ASTM D2650 – 04, Standard Test Method for Chemical Composition of Gases By Mass Spectrometry
(November 2004)
This test method is applicable for the quantitative analysis of gases containing specific combinations of the
following components: hydrogen; hydrocarbons with up to six carbon atoms per molecule; carbon
monoxide; carbon dioxide; mercaptans with one or two carbon atoms per molecule; hydrogen sulfide; and
air (nitrogen, oxygen, and argon). This test method is not applicable for the determination of constituents
that are present in amounts less than 0.1 mole %. This test method was developed on a specific type of
Mass Spectrometer, thus users of other instruments may have to modify operating parameters and the
calibration procedure and adapt it to their instrument.
The method sets out the experimental procedures, while the calculation procedures will depend on the
knowledge of qualitative mixture composition; errors due to components presumed absent; minimum cross
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