A Purification Method for Nickel from Seawater for Isotope Analysis

Nickel (Ni) is an important micro-nutrient in oceanic environments, typically with low surface concentrations that increase with depth. Ni isotope analyses offer the potential to provide insight into the cycling of Ni throughout the oceans. However, accurate and precise isotopic analysis requires the separation of Ni from the complex seasalt matrix. At USF, we have previously used a two-stage method involving batch extraction by Nobias PA-1 chelating resin and AGMP-1 anion resin to separate Fe, Zn, and Cd from major salts in seawater, but we found that this method is not effective for separating Ni from Na. Therefore, in order to comprehensively investigate Ni isotope distributions, a different method for separating the trace metal from the large concentrations of major cations present in seawater was needed. Here, we present a new chemical purification method that separates the typical trace amounts of Ni from the high concentrations of major salts (Na and Mg) in seawater, allowing isotopic analysis. Our method builds upon our existing published methods using Nobias PA-1 and AGMP-1 resins by incorporating a second Nobias PA-1 resin micro-column. This extra column allows us to fully separate Ni from Na, Mg and other interfering elements, before analysis of Ni by double spike mass spectrometry via Thermo Neptune MC-ICPMS. We also present new Ni isotope data from isotope standards, reference materials and Atlantic seawater samples.