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Van Der Veen A.M.H.,VSL | Hafner K.,VSL | Hafner K.,Institute of Metrology of Bosnia and Herzegovina IMBIH
Metrologia | Year: 2014

The publication of the standard atomic weights of 2009 by IUPAC raised the question of to what extent these changes affect the calculated composition of reference and calibration gas mixtures and the associated measurement uncertainty. The smallest uncertainties are attainable in the gravimetric gas mixture preparation, so the assessment was made for this technique. For the first time, the uncertainty contributions to the overall budget due to weighing, molecular weights, and composition of the parent gases are reported separately. The calculations show that even with the standard atomic weights of 2007, the uncertainty contribution due to the molecular weights can be of the same order as that due to weighing. The standard atomic weights of 2009 and 2011, when used under the same assumptions, increase the uncertainties of the amount-of-substance fractions of the abundant components from high-purity parent gases sometimes appreciably. Based on these calculations and the fact that the atomic weight intervals include sources that are unlikely to be generally relevant for measurements supporting trade, commerce, health and safety, there is a need to make a more in-depth analysis of the atomic weights used in calculations, and to reflect the knowledge about the isotopic composition of relevant materials in the value assignment and uncertainty calculation. © 2014 BIPM & IOP Publishing Ltd.

Jotanovic A.,Institute of Metrology of Bosnia and Herzegovina IMBIH | Suljagic S.,Institute of Metrology of Bosnia and Herzegovina IMBIH
Accreditation and Quality Assurance | Year: 2015

The laboratory for precious metals within the Institute of Metrology of Bosnia and Herzegovina acts as a state reference laboratory in the field of quality control of articles manufactured of precious metals, e.g. jewellery. It disseminates reference values through the organisation of proficiency testing (PT) schemes. Two separate PT schemes for the determination of mass fraction of gold in typical jewellery alloys were conducted in 2013 and 2014. Laboratories taking part in these PT schemes are affiliated to the National Metrology Institutes of several countries and two private goldsmith laboratories. Different approaches in the design of the PT schemes and the evaluation of the PT results were used with the purpose of exploring their features regarding the interpretation of the results. For PT.13, z-scores were used as laboratory performance indicators. The assigned value and the standard deviation for proficiency assessment were calculated from the results of the participating laboratories by applying robust statistic. z-score and z′-score were used as performance indicators for the scheme PT.14, and the assigned value of the test sample and its measurement uncertainty were determined by the PT provider. The standard deviation of the testing method of 0.5 mg/g as prescribed in ISO 11426 as fit for purpose in the field of interest is used as standard deviation for proficiency assessment σp. By comparing the z-scores and z′-scores assigned to the PT.14 results, it is evident that the measurement uncertainty of the assigned value provided by the PT provider does not affect the overall successfulness of the participants. The Q-score based on relative deviation was used as an alternative approach to identify future partners in PT schemes with the purpose of reference value assignment (Q ≤ 0.05). © 2015 Springer-Verlag Berlin Heidelberg

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