Automated analysis of natural variations in isotopes of silicon by the thermal decomposition of BaSiF6

Abstract

The performance of a new inlet system, the Nu Sil, for the automated determination of the isotopic abundances of silicon in SiF₄ gas generated from the thermal decomposition of BaSiF₆ is reported. The inlet system is coupled to an isotope ratio mass spectrometer through a conventional dual inlet system. The method uses straightforward and proven sample preparation chemistry that is suitable for converting the silicon in biogenic and lithogenic solids, or that dissolved in fresh or salt waters, to BaSiF₆. Yields of silicon tetrafluoride are 99.8 ± 0.16%. δ³⁰Si values obtained with the method for a variety of natural and synthetic materials agree with published values to better than 0.05‰. External long-term average δ³⁰Si values of the solid standard NBS28, the secondary standards Big Batch and diatomite, and the reference seawater ALOHA₁₀₀₀ are all within 0.03‰ of their respective consensus values. Typical loading of BaSiF₆ represents 10 to 40 μg of Si. The analytical rate is 30 unattended analyses daily.