Silicon isotope abundance ratios and atomic weights of NBS-28 and other reference materials

The silicon isotope abundance ratios and atomic weights of NBS-28 and several other silicon isotope reference materials were determined in this study. For the calibration of the measurement procedure, two new synthetic isotope mixtures were prepared gravimetrically from highly enriched silicon isotope materials in the form of SiO₂. All materials were converted into SiF₄ gas and subsequently their silicon isotope ratios were measured on the SiF₃⁺ species by using a gas source mass spectrometer MAT-253. The calibrated isotope abundance ratios of NBS-28 are 0.0507446 (26) for ²⁹Si/²⁸Si and 0.0341465 (15) for ³⁰Si/²⁸Si. The corresponding isotopic abundances are 92.17515(28)% for f(²⁸Si), 4.67739(24)% for f(²⁹Si) and 3.14746(14)% for f(³⁰Si). The silicon molar mass of NBS-28 is determined to be 28.08653(11), which is 0.001 larger than previously reported values. In the meanwhile, the ²⁹Si/²⁸Si and ³⁰Si/²⁸Si isotope abundance ratios and atomic weights of SRM-990, IRMM-017, IRMM-018, GBW-04421 and GBW-04422 are also calibrated. These new calibrated data can improve the reliability and comparability of silicon isotope results using above calibrators.