Silicon Isotope Analyses of Soil and Plant Reference Materials: An Inter-Comparison of Seven Laboratories

The use of silicon (Si) isotopes has led to major advances in our understanding of Si cycling in modern and past environments. This inter-laboratory comparison exercise provides the community with the first set of soil and plant reference materials with an analytically challenging matrix containing organic material that is known to induce isotopic bias, for use as secondary reference materials in Si isotope measurement. Seven laboratories analysed four soil reference materials (GBW-07401, GBW-07404, GBW-07407, TILL-1) and one plant reference material (ERM-CD281). Participating laboratories employed a range of chemical preparation methods and analytical setups but all analyses were performed by MC-ICP-MS. Irrespective of the chemical preparation method or analytical conditions, the results show excellent agreement among laboratories within 2s for at least three replicates. Data were combined together to calculate delta Si-29 and delta Si-30 mean values (relative to NBS 28) and their expanded uncertainties (U, coverage factor k = 2). The delta Si-30 values are as follow: GBW-07401: -0.27 +/- 0.06 parts per thousand, GBW-07404: -0.76 +/- 0.12 parts per thousand, GBW-07407: -1.82 +/- 0.17 parts per thousand, TILL-1: -0.16 +/- 0.06 parts per thousand and ERM-CD281: -0.28 +/- 0.11 parts per thousand. Also, a compilation of published data provides an up-to-date mean delta Si-30 for BHVO-2 of -0.28 +/- 0.08 parts per thousand.

Automated summary

The use of silicon isotopes has led to significant advancements in understanding silicon cycling in various environments. This inter-laboratory comparison exercise provided soil and plant reference materials with organic material, resulting in excellent agreement among seven laboratories using different analytical setups. The data obtained will serve as valuable resources for future research on silicon isotopes.