NPL provides primary reference natural gas mixtures (PRGMs) for sale. Each standard can contain single or multi-component species and is carefully prepared to meet specific customer requirements.

NPL's natural gas PRGMs are typically used to calibrate gas analysers, enabling determination of the composition of real natural gases, this allows accurate calculation of the calorific value and physical properties of the gas.

NPL also supplies natural gas odorant standards. A flyer detailing NPL's range of natural gas and sulphur odorant standards is available for download ( PDF 4.18 MB).

Scope of UKAS Accreditation

The preparation and analysis of these standards forms part of NPL's UKAS Reference Materials (Guide 34) and Calibration (ISO 17025) scopes of accreditation. Each standard is prepared gravimetrically (in accordance with ISO 6142) and analysed (in accordance with ISO 6143 and ISO 6974-2) against internationally recognised standards by NPL's own QA laboratory. A full list of accredited components, amount fraction ranges and best measurement capabilities is given in the table below:

Component	Amount Fraction Range (% mol/mol)	Best Measurement Capability (% mol/mol)
Methane	55.0 - 99.9	0.018 % relative + 0.002
Nitrogen	0.02 - 25.2	0.18 % relative + 0.00038
Carbon dioxide	0.04 - 25.0	0.20 % relative + 0.00045
Ethane	0.008 - 18.0	0.28 % relative + 0.00008
Propane	0.008 - 8.0	0.30 % relative + 0.00008
i-butane	0.004 - 1.7	0.40 % relative + 0.00004
n-butane	0.004 - 1.7	0.40 % relative + 0.00004
neo-pentane	0.0005 - 0.50	0.80 % relative + 0.000015
i-pentane	0.0025 - 0.60	0.40 % relative + 0.00003
n-pentane	0.0025 - 0.60	0.40 % relative + 0.00003
n-hexane	0.0008 - 0.50	0.40 % relative + 0.000018
Helium	0.0014 - 0.50	0.95 % relative + 0.00005
Component	Amount Fraction Range (μmol/mol)	Best Measurement Capability (μmol/mol)
Benzene	5 - 500	1.1 % relative + 0.03
Toluene	5 – 250	1.1 % relative + 0.03
Cyclohexane	10 – 400	1.1 % relative + 0.03
Methylcyclohexane	10 – 400	1.1 % relative + 0.03
n-heptane	10 – 500	1.15 % relative + 0.04
n-octane	5 – 200	1.3 % relative + 0.025 (for 5 to 10 µmol/mol) or 1.15% relative + 0.04 (for 10 to 200 µmol/mol)
n-nonane	1 – 120	1.64 % relative + 0.009 (for 1 to 10 µmol/mol) or 1.25% relative + 0.048 (for 10 to 120 µmol/mol)
n-decane	1 – 20	1.65 % relative + 0.013

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

Related standards and services

In addition to its range of natural gas standards, NPL also:

• Provides a UKAS accredited range of natural gas odorant standards
• Provides a range of refinery gas standards
• Organises proficiency testing (PT) schemes to enable laboratories to achieve
  greater confidence in their analyses of natural gas and refinery gas composition
• Provides a range of LPG, LNG and other liquid hydrocarbon standard mixtures

Contact

Customer Service tel: +44 20 8943 8637
E-mail: gases_enquiries@npl.co.uk