Silicon Isotope Amount Ratios and Molar Masses for Two Silicon Isotope Reference Materials: IRMM-018a and NBS28

A new 2 kg batch of SiO2 crystals, IRMM-018a as well as the existing NBS28 silica sand (or RM 8546, obtained by I. Friedman from U.S. Geological Survey) have been characterised for their "absolute" silicon isotope composition and molar mass. The amount of substance measurements needed for that purpose were performed on the IRMM amount comparator (Avogadro II) on samples from these batches, which were converted to gaseous silicon tetra-fluoride (SiF4). The isotope amount ratio measurements were calibrated by means of synthesized isotope amount ratios in the form of synthetic Si isotope mixtures, the measurement procedure of which makes them SI-traceable. IRMM-018a is intended to be used as Isotope Reference Material for isotope amount measurements in geochemical and other isotope abundance studies of silicon. It is distributed in samples of about 0.1 mol and will replace IRMM-018 (exhausted).JRC.D.4-Isotope measurement