Perfluorosulfonated Ionomer-Modified Diffusive Gradients in Thin Films: Tool for Inorganic Arsenic Speciation Analysis

A new concept in speciation analysis based on the diffusive gradients in thin films (DGT) technique is described. By use of two sets of DGT devices, one set with perfluorosulfonated ionomer (Nation) diffusive membranes and the other with polyacrylamide, anionic and uncharged analytes can be fractionated on the basis of charge. The dual device method is applied to speciation analysis of dissolved inorganic arsenic species. Over the environmentally significant pH range, inorganic As-III exists as neutral H3AsO3, whereas As-V is present as anionic H2AsO4- and HAsO42-. The measured diffusion coefficient of As-III through the negatively charged Nation membrane is significantly larger than that of the As-V species, whereas diffusion rates are similar through polyacrylamide diffusive gels. Hence, after simultaneously deploying DGT devices with and without Nation membranes, measurement of the amount of accumulated As in each type of device enables the concentration of both oxidation states to be determined.