INTERCOMPARISON OF A RANGE OF PRIMARY GAS STANDARDS OF CARBON-MONOXIDE IN NITROGEN AND CARBON-DIOXIDE IN NITROGEN PREPARED BY THE NATIONAL-INSTITUTE-OF-STANDARDS-AND-TECHNOLOGY AND THE NATIONAL-PHYSICAL-LABORATORY

Measurements were carried out by the National Physical Laboratory (NPL) in the United Kingdom and the National Institute of Standards and Technology (NIST) in the United States to intercompare the primary gravimetric gas standards developed by these two laboratories. These intercomparisons involved analyses of a set of CO and CO2 NIST Standard Reference Materials by the NPL, and of a similar set of NPL primary standards by the NIST. In each case, the exact concentrations of the exchanged sets were unknown to the analyzing laboratory. The CO and CO2 standards ranged in nominal concentration from 8% to 10 ppm and from 8% to 0.5%, respectively. The analyses were carried out using primary gravimetric standards, which were independently produced by the two laboratories. The mean difference between the values assigned by the supplying laboratory and the values determined by the analyzing laboratory was less than 0.2% relative for both sets of CO and CO2 standards. The results confirmed that standards produced by NPL and NIST have a high degree of consistency, and that measurements obtained using these standards for measurements of levels of atmospheric CO and CO2 may be directly intercompared.