Abstract. During the protocol development phase of CCQM-K16, interest was shown by two more national metrology institutes (NMIs) in participating in the comparison, but rather as a study instead of a key comparison. Therefore it was decided to organize in parallel to CCQM-K16 a study, CCQM-K49, enabling NMIs that did not wish to participate in the key comparison to participate in a study with mixtures with the same nominal specifications. The natural gas mixtures type IV (low calorific mixture) and type V (high calorific mixture) have been prepared and checked in the same time frame as those for CCQM-K16.

The protocol used for CCQM-P49 differed only in two aspects from that of CCQM-K16: (1) the results would be reported as results from a CCQM study, and (2) it was permitted that NMIs did not analyse all components present in the mixtures. The measurements in this comparison took place in 2001. There were two participants. The coordinating laboratories were the same as in CCQM-K16. The reference value for each component was based on the gravimetric preparation for all components.

For most components, the results of the participating NMIs agreed within 1% relative of the reference value.

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The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the Mutual Recognition Arrangement (MRA).