Coupling DGT passive samplers and multi-collector ICP-MS: a new tool to measure Pb and Zn isotopes composition in dilute aqueous solutions

Abstract : Using zinc (Zn) and lead (Pb) isotopes is a powerful tool to track metal pollution in environment. In this study we have developed the coupling between DGT passive samplers and multi-collector ICP-MS to measure Pb and Zn isotopic ratios in dilute aqueous solutions. The benefits of this coupling are multiple: the use of DGT device allows achieving an isotopic composition of natural water integrated over time and to pre-concentrate metals in situ. This development will greatly facilitate the field collection of samples and their preparations in cleanroom prior to their isotopic analyses. To test the capability of DGT samplers a series of experiments was achieved in cleanroom and in experimental pilot simulating a water flow. These tests have shown that there is no fractionation of Pb isotopes due to the use of DGT within the reported precision of MC-ICPMS measurements. For Zn, the diffusion process through a membrane, inherent to the use of DGT device, induces a fractionation between the isotopic composition obtained by the DGT and the natural composition. However, this bias can be easily corrected by using a simple relation independent of the time of exposure and the thickness of diffusion layer. The coupling DGT passive samplers and multi-collector ICP-MS is suitable to determine the Pb and Zn isotopic compositions in natural waters and offers new perspectives to track the anthropic pollutions in the hydrosphere.