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- Isotope amount ratio (3)
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Eingeladener Vortrag
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Roadmap for the purity determination of pure metallic elements – Basic rinciples and helpful advice
(2018)
High purity materials can serve as a realisation of the Système International d’Unitès (SI) unit amount of substance for the specific element. Solutions prepared from such high purity materials using gravimetric preparation and the concept of molar mass are used as calibration solutions in many fields of analytical chemistry. Calibration solutions prepared this way provide the traceability to the SI and are the metrological basis in elemental analysis.
The preparation and characterization of such primary pure substances, representing the realisation of the SI unit amount of substance, is undertaken only by a small number of National Metrology Institutes (NMI) and Designated Institutes (DI).
Many other NMIs and DIs, however, prepare elemental calibration solutions as calibrants for their measurement services, such as the certification of matrix Reference Materials or the provision of reference values for Proficiency Testing schemes. The elemental calibration solutions used for this purpose are not a direct service to customers, such as preparing secondary calibration solutions, but provide the source of traceability for the other services. Hence, it is necessary for the NMI or DI to obtain data on the purity of the pure metals or other materials used to prepare the solutions with measurement uncertainties meeting the needs of the above described services. This is commonly undertaken as a “fit for purpose” assessment, appropriate for the uncertainty requirement of the service provided to customers.
As a consequence, total purity measurements are a long-term strategy of CCQM-IAWG. Several studies were conducted (CCQM-P107, CCQM-K72 and CCQM-P149) on the measurement of the purity of zinc. From these studies, several conclusions can be drawn for the purity assessment of a pure (metallic) element. These conclusions will be put together in this document in order to assist all NMIs/DIs in performing a purity assessment, whenever needed.
Absolute Isotope Ratios
(2018)
Measurement results and scientific models leading to important decisions in forensics, food fraud or climatology are based on isotope ratio data. Molar masses of multi-isotopic elements are as well based on isotope ratio data. Thus, in the case of Si, isotope ratios directly impact the redefinition of the SI base units kilogram and mole. Therefore, new strategies are required leading to new primary isotope reference materials, whose isotope ratios are traceable to the SI. This in turn will ensure the comparability of isotope ratio data and will render the traceability exception requested by the CCQM superfluous. Such new procedures will be developed for the key elements S, Si, Ca, Sr and Nd at relative uncertainty levels of ≤ 0.01 %.
This presentation gives a short overview of isotope ratio measurements being carried out in the past few years at BAM in different fields such as plant metabolism, food web structures and archaeology. The corresponding isotope reference materials which have been certified at BAM in parallel are presented as well. Additionally an outlook is being provided on future iRM projects.