High precision analysis of mercury isotopes at ultra-low concentrations using dry cold vapor generation-MC-ICP-MS

Abstract

High-precision analysis of mercury (Hg) isotope compositions is fundamental for tracing the Hg cycle in the environment. However, accurate and precise Hg isotope analysis for samples with low Hg concentrations (sub-ppb level) remains one of the most prominent challenges in the analysis and application of Hg isotopes. In this study, we developed a new method for high-precision Hg isotope analysis using a dry cold vapor generation (dry-CVG) system coupled to MC-ICP-MS. The dry-CVG system removed water content from the Hg(0) cold vapor and thus significantly inhibited the formation of oxides and hydrides, providing better signal intensity, stability and precision for Hg isotope analysis. Under optimized conditions, the analytical uncertainties were ±0.07‰ and ±0.06‰ (2SD) for δ²⁰²Hg and Δ¹⁹⁹Hg, respectively at a concentration of 0.1 ng mL⁻¹ (0.75 ng Hg consumption), which is comparable to the typical precision reported in the literature but obtained at 10-fold higher Hg concentrations. Moreover, our method substantially improved the precision for Hg isotope analysis at higher concentrations (≥2.0 ng mL⁻¹), reaching ±0.02‰ and ±0.01‰ (2SD) for δ²⁰²Hg and Δ¹⁹⁹Hg, respectively. The accuracy and precision of this method were further verified using a variety of certified reference materials with different types of natural matrices (including plant, soil and sediment). Thus, our method provides a promising approach for accurate Hg isotope analysis at low concentrations with high precision, and may expand the future application of Hg isotopes in geochemical and environmental studies.