Determination of strontium isotope ratios in plant samples by wet ashing digestion

Abstract

Strontium isotope provenance analysis has been widely applied across multiple disciplines, including archaeology, food science, and forensics. The establishment of bioavailable ⁸⁷Sr/⁸⁶Sr maps, known as isoscapes, which rely on a substantial number of plant ⁸⁷Sr/⁸⁶Sr values, serves as the cornerstone for such provenance studies. The conventional dry ashing method for plant samples is laborious, time-consuming, and constrained by limited equipment capacity, which impedes large-scale plant ⁸⁷Sr/⁸⁶Sr analysis. The wet ashing method that employs hydrogen peroxide (H₂O₂) and strong acids to decompose the organic matter in plants has attracted growing interest, with the expanding applications of strontium isotopes and the increasing demand for large datasets. Microwave-assisted wet ashing (microwave digestion) has shown considerable promise for plant strontium isotope analysis of large datasets. This study collected 22 plant samples from diverse geological regions across the Tibetan Plateau, employing both dry and traditional wet ashing methods for sample preparation prior to ⁸⁷Sr/⁸⁶Sr analysis, with the aim of systematically assessing the applicability of wet ashing for plant strontium isotope studies. Results show comparable ⁸⁷Sr/⁸⁶Sr values from both methods. Notably, compared to dry ashing, wet ashing offers a more straightforward and efficient alternative, making it particularly well-suited for large-scale measurements of ⁸⁷Sr/⁸⁶Sr values. This finding not only validates the feasibility of wet ashing in strontium isotope analysis, but also establishes a theoretical foundation for the optimization and broader implementation of microwave digestion technology in plant strontium isotope analysis.