CCQM Activities in the Gas Analysis Working Group

NIST's Analytical Chemistry Division Gas Metrology group has participated in over 20 Consultative Committee for Amount of Substance-Metrology in Chemistry (CCQM) Gas Analysis Working Group (GAWG) Key Comparison studies since 1993. The CCQM conducts international Key comparisons to establish equivalence among measurements made by national metrology institutes (NMIs). GAWG Key Comparisons during the past two years included measurement of ammonia, hexane, propane, mercaptans, ozone, oxygen, carbon monoxide, carbon dioxide, nitric oxide, and sulfur dioxide.

The results from these Key comparisons will be used to benchmark the appropriate Calibration and Measurement Claims (CMCs) of the participating NMIs. CMCs are basically the declared capabilities that an NMI offers to customers, and they are included in a searchable database at the BIPM web site. CMCs that are common among the NMIs are identified appropriate comparisons proposed. NIST CMCs are benchmarked based on carefully designed and executed comparisons using the methods normally used for those analyses for NIST's customers.

The technical approaches used for the GAWG Key Comparisons are the same as those used for the CMCs. In this way, the CMCs can be benchmarked through the CCQM studies. The GAWG has decided to conduct two types of Key Comparisons: 1) the Core Key Comparisons and 2) Analytical Challenge Key Comparisons. The Core Key Comparisons will test an NMI's core capabilities to produce gas standards, and each NMI will be required to participate in these exercises periodically. An example is an upcoming Key Comparison on 100 µmol/mol sulfur dioxide that NIST will coordinate in 2010. These comparisons will be very broad in scope and cover a large number of non-reactive gas CMCs. The Analytical Challenge Key Comparisons will cover a very narrow scope, usually only the compound being compared. An example of these comparisons is the recent ammonia key comparison which covers only ammonia in the concentration range of 10 µmol/mol to percent levels.

Major Accomplishments:

• CCQM-K46, Key Comparison of 30 to 40 µmol/mol Ammonia
• CCQM-K51, Key Comparison of 5 µmol/mol Carbon Monoxide
• CCQM-K53, Key Comparison (Preparative) of 100 µmol/mol Oxygen
• CCQM-K54, Key Comparison (Preparative) of 100 µmol/mol Hexane
• CCQM-K66 Purity of Methane
• CCQM-K68 320 nmol/mol Nitrous Oxide in Air
• CCQM-K71, Key Comparison emission levels of Sulfur Dioxide, Nitric Oxide, Propane, Carbon Monoxide, and Carbon Dioxide
• BIPM.QM-K1, Key Comparison of Ozone