Determination of Mn, Fe, Ni, Cu, Zn, Cd and Pb in seawater using offline extraction and triple quadrupole ICP-MS/MS

Abstract

Highly resolved temporal and spatial distributions of trace elements in ocean water can provide insight into ocean processes but carry a significant analytical demand which requires methods that combine accuracy and precision with high sample throughput. Here a multi-element method is presented which combines the commercially-available seaFAST preconcentration system with ICP-MS/MS for the analysis of Mn, Fe, Ni, Cu, Zn, Cd and Pb in seawater. Samples (20 mL or 40 mL) are loaded on to a chelation resin column and trace metals eluted into 2.5 mL of 1.6 N HNO₃. Analysis of the eluate was carried out by ICP-MS/MS, which combines two mass-selecting quadrupoles separated by an octopole collision/reaction cell. The collision/reaction cell was pressurized with O₂ gas for the analysis of Mn, Ni, Cu, Cd and Pb and H₂ gas for the analysis of Fe and Zn, which removed common interferences (e.g. ArO⁺ on ⁵⁶Fe and MoO⁺ on Cd) yet maintained the highest instrument sensitivity across the entire mass range. Measured blanks and detection limits were ≤0.050 nmol L⁻¹ levels, except for the Fe (blank 0.14 nmol L⁻¹) and were suitable for open-ocean seawater analysis. We report results for the certified reference material NASS-6, consensus reference standards SAFe S and SAFe D and depth profiles of trace metals from the Arctic Ocean, collected as part of the Canadian GEOTRACES program.