Improvement of Digestion and Purification Steps for the Determination of Soil Zn Isotopes by MC‐ICP‐MS

Abstract

Despite the determination of zinc (Zn) isotope in soil being undertaken by several laboratories worldwide, sample preparation steps are varied due to diverse soil properties and compositions. This paper proposes a widely applicable soil acid digestion procedure that has been thoroughly evaluated for both soil and geological reference materials. To ensure the general applicability of this method to large varieties of soil samples, synthetic multi‐element solutions of high matrix element: Zn ratios (M/Zn) were prepared by embracing all possible elemental compositions of forty‐three certified reference materials; the chemical preparation procedure was then tested and optimised using these synthetic solutions. Results show that the recovery rate of Zn could reach 99–100% after the pre‐treatment. Based on this method, the δ66/64Zn data relative to JMC‐Lyon 3‐0749L Zn of previously uncharacterised NIST reference materials (including SRM 2709a San Joaquin soil, SRM 2710a Montana Soil and SRM 2711 Montana Soil) and Chinese certified reference materials (GSS‐1a, GSS‐7a, GSS‐5, GSS‐8, GSS‐14, GSS‐18, GSS‐20, GSS‐24, GSS‐31) were measured using MC‐ICP‐MS with a range from ‐0.08‰ to 0.35‰. The Zn isotope compositions of twenty‐nine soil samples from twenty‐one provinces/municipalities across China were also analysed and were found to fall within typical ranges from ‐0.09‰ to 0.28‰. The intermediate precision of several pure Zn standard solutions was better than ± 0.05‰ (2s) over 22 months of measurement. This method and results are useful for comparison and calibration of data between laboratories as well as providing a solid reference soil dataset for future studies dealing with Zn isotopes.