Multielemental Isotopic Analysis for Trace Metals in Geochemical Samples, Part 1: Dissolved Iron, Nickel, Copper, Zinc, Cadmium, and Lead in Seawater

Isotope ratios of dissolved trace metals in seawater are useful for understanding marine biogeochemical cycles; however, the analysis requires considerable time and effort to concentrate trace metals from seawater and remove high concentrations of alkali and alkaline earth metals. This paper introduces a novel method for the simultaneous analysis of isotope ratios for Fe, Ni, Cu, Zn, Cd, and Pb in seawater using solid-phase chelate extraction and anion exchange. The process involves chelate extraction with a NOBIAS Chelate PA1 resin column to concentrate Fe, Ni, Cu, Zn, Cd, and Pb while removing alkali metals, alkaline earth metals, and Mo. Subsequent anion exchange using an AG MP-1 M column separated Fe, Ni, Cu, Zn, Cd, and Pb from each other. The recoveries for Fe, Ni, Cu, Zn, Cd, and Pb during the entire chemical separation process exceed 94%, and the total procedure blanks are only 4 pmol/kg for Fe, 0.3 pmol/kg for Ni, 1.3 pmol/kg for Cu, 0.9 pmol/kg for Zn, 0.03 pmol/kg for Cd, and 0.01 pmol/kg for Pb. Seawater samples from Suruga Bay, Japan are analyzed to evaluate the accuracy and precision of isotopic analysis for Fe, Ni, Cu, Zn, Cd, and Pb. Using this method, isotope ratios of Fe, Ni, Cu, Zn, Cd, and Pb were determined in reference seawater materials (GSC, NASS-7, and CASS-6) and seawater samples that were collected at a station in the North Pacific. Despite involving only two chemical separation steps, this method accurately analyzes the isotope ratios from a single seawater sample, significantly reducing the processing time, labor, reagents, and seawater samples required for analysis.