Natural gas (NG) is one of the most important
sources of energy for industrial and domestic consumption in the present era
because it is cheap and free from sulfur impurities. Therefore, accurate and
precise measurement of its composition is of fundamental importance for trade
reasons. To improve the quality of NG gas measurements, certified reference
materials (CRMs) should be used for calibration of measuring equipment in order
to ensure the traceability of the measurement results to the SI units. For the
traceability purpose, a multicomponent natural gas mixture was prepared
gravimetrically as a reference material according to ISO 6142 from pure helium,
hydrogen, n-pentane, i-pentane, n-butane, i-butane, propane, ethane, hexane,
methane and nitrogen. The preparation was done in two dilution steps in 5L aluminum cylinders. The calculated mole fractions and associated
uncertainties of natural gas components were verified by a dual GC-FID/TCD
system in accordance with ISO 6143 calibrated by a series of primary gas
mixtures (CRMs) produced by an NMI. The results obtained by gravimetry and by
GC measurements have been checked for compatibility as required by ISO 6142 and
were found in very good agreement. Details of the preparation and calculation
of the mole fractions and uncertainties of all gas components are explained in this
article.
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