Quantification of Re and four other trace elements (Ag, Cd, Pd, Zn) in certified reference materials and natural waters

Abstract

Rhenium is the third least abundant element of the Earth's upper continental crust, and typical aquatic concentrations are in the ng L⁻¹ range. Despite these natural ultra-trace levels, Re is a powerful geochemical tracer for weathering and redox processes. Here, we report a simple chemical separation method (i.e., single column and single elution) using an anion exchange resin (1-X8) to quantify Re and four co-eluted elements (Ag, Cd, Pd, Zn) from fresh and seawater matrices. The method was tested for the three most used water certified reference materials (CRMs): freshwater SLRS-6 and seawaters CASS-6 and NASS-7; the pre-concentration factor was 25–50 times. In addition to validating the method for Cd and Zn against their certified concentrations, we report the concentrations for Re (6.0–6.4 ng L⁻¹ for seawater CRMs and 13.8 ± 0.6 ng L⁻¹ for SLRS-6) and Ag (0.7–1.1 ng L⁻¹ for seawater CRMs and 2.7 ± 0.4 ng L⁻¹ for SLRS-6) for QA/QC validation of future works. We also applied the method to natural coastal seawater similar to CASS-6 and NASS-7 at a pre-concentration factor of 1000 yielding adequately low limits of detection for Pd in the sub pg L⁻¹ range. The concentrations of Ag, Cd, Re, Pd and Zn measured in fresh and seawater CRMs, and natural samples were consistent with their anticipated environmental backgrounds. The method outlined here allows the quantification of five trace and ultra-trace elements, each exhibiting contrasting biogeochemical behaviours, and thus could contribute to advancing our understanding of their environmental cycling by significantly simplifying analytical workflows.