Hamburg 2009 – wissenschaftliches Programm
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MS: Fachverband Massenspektrometrie
MS 8: Speicherringe, ICP-MS, Neue Entwicklungen
MS 8.7: Vortrag
Mittwoch, 4. März 2009, 15:30–15:45, VMP 8 R05
Multicollector-ICP-Mass Spectrometry for Trace Analysis of Silicon Crystals — •Axel Pramann, Olaf Rienitz, and Detlef Schiel — Physikalisch-Technische Bundesanstalt, Braunschweig, Germany
The measurement of the molar mass of highly pure silicon is a challenging task of an international project for the re-determination of the Avogadro constant1 on a relative uncertainty level of 10−8. At PTB a MC-ICP-Mass Spectrometer (NeptuneTM, ThermoFinnigan) is used to measure isotope ratios 28Si/29Si and 30Si/29Si of the silicon WASO17 crystal. This experiment is used to validate and optimize the current data received by gas mass spectrometry at IRMM.1 Based on a new method for the analytical determination of calibration (K) factors which will be described elsewhere, both the principal proof of the ability of this method as well as a new chemical preparation route in combination with MC-ICP-MS has been demonstrated for the first time. The reported method shows the ability of the determination of molar masses traceable to the SI units. Details of the experiment and the way of sample preparation are described. First measurements show a repeatability of the K factors in the range of srel = 0.1 …0.4 %. The abundance of Si isotopes 28Si, 29Si, and 28Si in various Si crystal samples is determined by applying the K factors. Isotope ratios show standard uncertainties urel( 30Si/29Si) = 0.13 % and urel( 28Si/29Si) = 0.6 %. The study is completed with an uncertainty budget according to the guide to the expression of uncertainty in measurement (GUM).
1P. Becker, Metrologia 40, 366 (2003).