Abstract
Isotope ratio analysis using MC ICP-MS is a powerful and precise tool for environmental analytics. One element well studied within this context is Pb. Pb acts as a tracer for different anthropogenic impacts on the environment, changes in its isotopic ratios provide valuable analytical information e.g. about the source the anthropogenic Pb inputs. One area prone to anthropogenic impact are coastal seas, as the waterbody is directly impacted by riverine inputs, atmospheric deposits and direct emissions e.g. originating from shipping. Indeed, the ultra-trace concentrations of Pb in seawater makes it challenging to quantify and to purify samples for isotopic analysis in sufficient quantity. In this study we present two preconcentration methods for Pb isotopic ratio measurement via MC ICP-MS in seawater. One approach features freeze drying of the seawater with subsequent first matrix removal and preconcentration using an offline seaFASTTM system (Elemental Scientific) utilizing Nobias-PA-1 chelating resin. The second approach features a pressure filtration using Empore™ SPE Chelating Disks (CDS Analytical) for parallel preconcentration and first matrix removal. Further purification for both approaches was conducted by a fully automated separation of Pb using DGA Resin (TrisKem International) (Pb recovery >93%) as described by Retzmann et al. (2017). MC ICP-MS (Nu Plasma II, Nu Instruments Ltd.) measurements were conducted in static measurement mode with low mass resolution. Correction for instrumental isotopic fractionation (IIF) was based on standard-sample bracketing adapted from Horsky et al. (2016). Both methods were tested for matrix removal efficiency, Pb recovery and potential isotopic fractionation to develop a new reliable and robust method for Pb isotopic analysis in seawater.
