First determination of iodide in natural water using diffusive gradient in thin-film techniques

Measuring the redox speciation of iodine in aquatic environment is a current analytical challenge due to the low concentration of iodine species, sampling and analytical issues linked to the iodine chemistry (redox instability, volatility, etc.). We propose to resolve some of these issues by using the Diffusive Gradient in Thin film (DGT) technique, which is a dynamic passive sampling technique. The DGT sampling allows the preconcentration of the target species leading to the improvement of their determination by chemical analysis. Moreover, the combination of two DGT methods with different selectivities opens up possibilities for redox speciation analysis. The power of this approach to study the behavior of some redox sensitive elements like As, Cr, Hg, has already been demonstrated. Within this framework, developing new specific DGT binding gels for iodine species could be useful to improve knowledge on geochemical behavior of iodine in aquatic environments. These important geochemical data could also allow a better risk assessment of nuclear facilities. The Ag doped-Cl (AgdCl) resin, developed by Triskem international, has already been used in extraction chromatography to selectively accumulate iodide (I-). In this work we present the first DGT application using the AgdCl resin in the binding gel. Laboratory investigations were performed to determine the selectivity and the accumulation capability of the AgdCl binding gel for the most common iodine species in aquatic environments. Key parameters such as iodide elution optimization, effective iodide diffusion coefficient, ionic strength, pH and ion competing effects will be also presented. Finally, some results of time series-experiments in natural waters will be shown to validate performances of the new DGT method.