National Physical Laboratory

Natural gas

Natural gas

NPL's natural gas standards are typically used to calibrate gas analysers. This enables the composition of real natural gases to be determined, thus allowing accurate calculation of the calorific value and other physical properties of the gas.

In addition to the components usually found in synthetic natural gas standards (C1 to C5 alkanes, n-hexane, nitrogen and carbon dioxide), NPL's standards can also contain C6 to C10 hydrocarbon components. Accurate measurement of these components is particularly useful when hydrocarbon dew point is to be calculated, reassuring the gas transporter that condensation of the mixture will not take place in the gas pipeline.

The range of natural gas standards covered by NPL's UKAS accreditation is shown in the table below:

Component Amount fraction
range (cmol/mol) *
Methane 55.0 to 99.9
Nitrogen 0.02 to 25.2
Carbon dioxide 0.04 to 25.0
Ethane 0.008 to 18.0
Propane 0.008 to 8.0
i-butane 0.004 to 1.7
n-butane 0.004 to 1.7
neo-pentane 0.0005 to 0.50
i-pentane 0.0025 to 0.60
n-pentane 0.0025 to 0.60
n-hexane 0.0008 to 0.50
Helium 0.0014 to 0.50
Component Amount fraction
range (µmol/mol)
Benzene 5 to 500
Toluene 5 to 250
Cyclohexane 10 to 400
Methylcyclohexane 10 to 400
n-heptane 10 to 500
n-octane 5 to 200
n-nonane 1 to 120
n-decane 1 to 20

* 1 cmol/mol is equal to 0.01 mol/mol and is equivalent to the 'unit' % mol/mol often used by the natural gas industry

Other components

NPL's natural gas PRGMs may also contain other hydrocarbon isomers not listed in the above table. Examples of these components include, but are not restricted to:

  • cyclopentane
  • 2,2-dimethylbutane
  • 2,3-dimethylbutane
  • 2-methylpentane
  • 3-methylpentane
  • 2-methylhexane


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Last Updated: 29 Mar 2017
Created: 18 Sep 2013


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