Determination of Nine Elements including Ag, W, and Sb in Soils and Sediments by Helium Mode ICP-MS with Open-Vessel Acid Digestion and Its Application to Mineral Exploration

When determining Ag, W, Sb, Ba, Cu, Pb, Zn, Co and Ni in soil and sediment samples, W is difficult to dissolve and prone to hydrolysis, Sb is volatile at high temperatures, and the Ag isotopes (¹⁰⁷Ag and ¹⁰⁹Ag) are significantly interfered by Zr and Nb oxides during ICP-MS analysis. In this study, an open-vessel digestion method was employed using a mixture of three acids (nitric acid–hydrofluoric acid–perchloric acid), followed by re-dissolution with aqua regia at temperatures ranging from 120℃ to 150℃ and extraction with nitric acid. Rh and Re were selected as internal standard elements, and interference tests for Zr and Nb oxides on ¹⁰⁷Ag and ¹⁰⁹Ag were conducted separately in He mode. By combining He mode with offline interference correction, the interference of oxides ⁹¹Zr¹⁶O⁺ and ⁹³Nb¹⁶O⁺ on ¹⁰⁷Ag and ¹⁰⁹Ag was corrected, enabling the simultaneous determination of nine elements through one digestion, one sample introduction, and one mode. Method verification was performed using six soil and six sediment reference materials, which demonstrated that the method’s detection limit, precision, and accuracy exceeded the requirements specified in DZ/T 0130.4-2006. Compared with standard methods, the results were in compliance with technical specifications. The proposed method was then applied to the analysis of 1527 soil and sediment samples covering a broad range of nine elements. The reporting rate for these elements reached 100%, with the accuracy and precision of the monitoring samples (standard materials) aligning with specified requirements. The spatial distribution of the nine target elements, as revealed by geological mapping analysis, demonstrated strong correlations with stratigraphic units, structural features, lithological variations, and mineralization patterns. These mapping results aligned closely with the regional geological framework. Thus, this method addresses the technical difficulties associated with traditional ICP-MS determination, such as Ag interference and the simultaneous analysis of multiple elements including Ag, W, and Sb. Overall, the method is simple, efficient, and cost-effective.