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Rhoderick G.C.,U.S. National Institute of Standards and Technology | Duewer D.L.,U.S. National Institute of Standards and Technology | Ning L.,U.S. National Institute of Standards and Technology | Ning L.,Institute of Reference Materials | Desirant K.,SALt Inc
Analytical Chemistry | Year: 2010

Studies of climate change increasingly recognize the diverse influences exerted by hydrocarbons in the atmosphere, including roles in particulates and ozone formation. Measurements of key non-methane hydrocarbons (NMHCs) suggest atmospheric concentrations ranging from low pmol/mol to nmol/mol, depending on location and compound. To accurately establish concentration trends and to relate measurement records from many laboratories and researchers, it is essential to have good calibration standards. Several of the world's National Metrology Institutes (NMIs) are developing primary and secondary reference gas standards at the nmol/mol level. While the U.S. NMI, the National Institute of Standards and Technology (NIST), has developed pmol/mol standards for halocarbons and some volatile organics, the feasibility of preparing well-characterized, stable standards for NMHCs at the pmol/mol level is not yet established. NIST recently developed a suite of primary standards by gravimetric dilution that contains 18 NMHCs covering the concentration range of 60 pmol/mol to 230 pmol/mol. Taking into account the small but chemically significant contribution of NMHCs in the high-purity diluent nitrogen used in their preparation, the relative concentrations and short-term stability (2 to 3 months) of these NMHCs in the primary standards have been confirmed by chromatographic analysis. The gravimetric values assigned from the methods used to prepare the materials and the analytical concentrations determined from chromatographic analysis generally agree to within ±2 pmol/mol. However, anomalous results for several of the compounds reflect the difficulties inherent in avoiding contamination and making accurate measurements at these very low levels. © 2010 American Chemical Society. Source


Tian W.,Institute of Reference Materials | Liu T.,Institute of Reference Materials | Li N.,Institute of Reference Materials | Wu Z.-X.,Institute of Reference Materials
Jiliang Xuebao/Acta Metrologica Sinica | Year: 2010

Several SO2 primary gravimetric standards at the concentration of 50 μmol/mol and 1500 μmol/mol level are prepared by National Institute Metrology (NIM) and Institute for Environmental Reference Materials of MEP (IERM). The uncertainty analysis is discussed, and the expanded uncertainty is 1.3% and 0.9% for 50 μmol/mol and 1500 μmol/mol level. These primary gravimetric standards prepared by NIM and IERM are compared and also compared with the SO2 primary gravimetric standards prepared by national institute of metrology of Netherlands. The results indicated that the largest relative deviation is 0.88% for 50 μmol/mol concentrations of SO2 primary standards, 0.63% for 1 500 μmol/mol level. The relative deviations are smaller than the uncertainties analysis. The good agreement of the SO2 primary standard prepared by NIM and IERM, and their agreement with the international standard can meet the requirements of measurement traceability. Source

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