Si primary standards for the calibration of ion-current ratios in the molar-mass measurement of natural Si single crystals

A procedure is described to obtain SI-traceable silicon isotope amount ratios in the BaSiF 6 form. On the basis of a gravimetric approach, three synthetic isotope mixtures were made, very similar to natural Si, by blending silicon isotopically enriched with 28 Si, 29 Si and 30 Si. These mixtures served as references to calibrate measurements of (SiF 3 ) + current ratios. In this way, it was possible to make SI-traceable measurements of silicon isotope amount ratios, without any assumptive correction. The isotopic composition of the natural Si crystal WASO17.2 was remeasured and its molar mass was redetermined.