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MS: Fachverband Massenspektrometrie

MS 2: Precision Mass Spectrometry

MS 2.7: Vortrag

Montag, 11. März 2019, 15:45–16:00, U A-Esch 2

The Revision of the SI: Mass spectrometry and the XRCD method used for a redefinition of the mole — •Axel Pramann, Olaf Rienitz, and Bernd Güttler — Physikalisch-Technische Bundesanstalt (PTB), Bundesallee 100, 38116 Braunschweig, Germany

The General Conference on Weights and Measures (CGPM) has voted for the revision of the SI on November 16, 2018. The SI base units will be realized and defined via fundamental constants. In case of the amount of substance, the SI unit mole will be defined via the Avogadro constant NA best accessible by applying the X-ray-crystal-density XRCD method by counting silicon atoms in single-crystalline silicon spheres [1]. In this approach, high-resolution MC-ICP-MS is a central experiment (determination of the molar mass M of the Si spheres). During the last decade the unceratinties u(M) were reduced by three orders of magnitude and the contribution of u(M) to u(NA) was reduced from 60% to 6%. The uncertainty obtained for urel(M) < 1 x 10-9 is unique in chemistry so far. The changes in chemistry and physics when using the amount of substance prior and after the revision are discussed using practical examples. Moreover, the dissemination of the amount of substance (mol) in the future is decribed [2].

[1] K. Fujii et al., Metrologia, 53, A19 (2016). [2] B. Güttler, O. Rienitz, A. Pramann, Annalen der Physik, accepted.