TY - JOUR A1 - Kipphardt, Heinrich A1 - Ding, T. A1 - Valkiers, S. A1 - Quetel, C. A1 - De Bièvre, P. A1 - Taylor, P. A1 - Gonfiantini, R. T1 - Preparation of two synthetic isotope mixtures for the calibration of isotope amount ratio measurements of sulfur N2 - Two synthetic isotope mixtures for the calibration of sulfur isotope amount ratio measurements were gravimetrically prepared from high purity Ag2S materials enriched in 32S, 33S, and 34S. The mixtures were made so as to closely resemble the (natural) isotopic composition of the materials to be “calibrated”. This allowed a totally independent evaluation, on the same samples, of the relative combined uncertainty of: (a) the procedure to perform direct measurements of the amount of substance ratios of gas isotopes in the redetermination of the Avogadro constant and (b) the gravimetric preparation procedure. The result of both procedures, mass spectrometry and gravimetry, agree to a relative uncertainty of 3 × 10-4 for sulfur amount ratio measurements of the major abundant isotopes. Thus it seems that a direct measurement of isotopic gas mixtures (e.g. of natural isotopic composition) is now possible for sulfur—and probably also for other gaseous isotopes—without necessarily having to rely on “calibration” by means of values provided by measurements of gravimetrically prepared isotope mixtures. However, synthetic mixtures may be needed for validation and verification purposes, in particular for quality assurance. KW - Sulfur KW - Absolute isotope amount ratio KW - Synthetic isotope mixtures KW - Sulfur hexafluoride KW - Mass spectrometry PY - 2000 U6 - https://doi.org/10.1016/S1387-3806(99)00235-3 SN - 0168-1176 SN - 0020-7381 SN - 1387-3806 SN - 1873-2798 VL - 197 IS - 1-3 SP - 131 EP - 137 PB - Elsevier CY - Amsterdam AN - OPUS4-913 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -