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We determined accurate values of ratios among the average molar masses M Ar of 9 argon samples using two completely-independent techniques: (1) mass spectrometry and (2) measured ratios of acoustic resonance frequencies. The two techniques yielded mutually consistent ratios (RMS deviation of 0.16 × 10 −6 M Ar from the expected correlation) for the 9 samples of highly-purified, commercially-purchased argon with values of M Ar spanning a range of 2 × 10 −6 M Ar . Among the 9 argon samples, two were traceable to recent, accurate, argon-based measurements of the Boltzmann constant k B using primary acoustic gas thermometers (AGT). Additionally we determined our absolute values of M Ar traceable to two, completely-independent, isotopic-reference standards; one standard was prepared gravimetrically at KRISS in 2006; the other standard was isotopically-enriched 40 Ar that was used during NIST's 1988 measurement of k B and was sent to NIM for this research. The absolute values of M Ar determined using the KRISS standard have the relative standard uncertainty u r (M Ar ) = 0.70 × 10 −6 (Uncertainties here are one standard uncertainty.); they agree with values of M Ar determined at NIM using an AGT within the uncertainty of the comparison u r (M Ar ) = 0.93 × 10 −6 . If our measurements of M Ar are accepted, the difference between two, recent, argon-based, AGT measurements of k B decreases from (2.77 ± 1.43) × 10 −6 k B to (0.16 ± 1.28) × 10 −6 k B . This decrease enables the calculation of a meaningful, weighted average value of k B with a uncertainty u r (k B ) ≈ 0.6 × 10 −6 .

We present the global research landscape which aims to deliver a measurement infrastructure to underpin atmospheric observations of key greenhouse gases governing changes in the Earth's climate. These measurements present a significant challenge to the metrological community, analytical laboratories and major producers of reference materials. The review focuses on the progress made in the Gas Analysis Working Group of the Consultative Committee for Amount of Substance: Metrology in Chemistry and Biology (CCQM-GAWG) in establishing the primary realisation of the amount-of-substance fraction for carbon dioxide, methane and nitrous oxide in an air matrix. It also focuses on the importance of providing traceable measurements of isotopic composition of these components for commutability of reference materials and for isotope ratio measurements for greenhouse gas source attribution. Metrologia 56 (2019) 034006 (29pp) P J Brewer et al 2 of the World Meteorological Organization (WMO) for providing the framework for the development and implementation of integrated greenhouse gas observations, which is vital for understanding the global carbon cycle and the role greenhouse gases play in climate change. The developments in analytical techniques are also discussed which have shaped the direction of the metrology required to meet the evolving and future needs of stakeholders.

Four new compounds, stigmastanol-3beta-p-glyceroxydihydrocoumaroate (1), stigmastanol-3beta-p-butanoxydihydrocoumaroate (2), lanast-7,9(11)-dien-3alpha,15alpha-diol-3alpha-D-glucofuranoside (3) and 1-phenyl-2-hydroxy-3,7-dimethyl-11-aldehydic-tetradecane-2-beta-D-glucopyranoside (4), along with several known compounds were isolated from the methanol extract of hulls of Oryza sativa. The new structures were established by one- and two-dimensional NMR and in combination with IR, EI/MS, FAB/MS and HR-FAB/ MS. Compound (3) strongly inhibited the growth of duckweed (Lemna paucicostata Hegelm 381), whilst compounds (2) and (4) exhibited weak inhibition.

In this study, standard gas mixtures of SF in synthetic air were gravimetrically developed as a suite consisting of 6 mixtures with mole fractions of SF ranging from 5 to 15 pmol/mol. For precision in weighing the gas fills, an automatic weighing system coupled with a high sensitivity mass balance was used and a gravimetry precision of 3 mg (2σ) was achieved. Impurity profiles of the raw gases were determined by various analyzers. In particular, sub pmol/mol levels of SF in the matrix components (N, O, and Ar) were carefully measured, since the mole fraction of SF in the final step can be significantly biased by this trace amount of SF in the raw gases of the matrix components. Gravimetric dilution of SF by purity-assessed N was performed in 6 steps to achieve a mole fraction of 440 pmol/mol. In the final step, O and Ar were added to mimic the atmospheric composition. Gravimetric fractions of SF and the associated standard uncertainty in each step were computed according to the ISO 6142 and JCGM 100:2008, respectively, and validated experimentally. Eventually, the SF fraction uncertainty of the standard gas mixtures combined by uncertainties of gravimetric preparation and verification measurements were found to be nominally 0.08% at a 95% confidence interval. A comparison with independent calibration standards from NOAA shows agreement within 0.49%, satisfying the extended WMO compatibility goal, 0.05 ppt.