The accurate measurement of solutes by DGT relies on the strength of their interaction with the binding layer.Mass transport of the analyte through the diffusive layer can only achieve a steady state when the analyte binds rapidly and irreversibly to the surface of the binding layer, so that the concentration of the solute at the interface between the binding layer and diffusive layer is effectively zero [1]. When this assumption is met, the DGT equation can be used to accurately determine the DGT-labile concentration of the analyte in the bulk solution. The first binding layer to be used with DGT consisted of a hydrogel containing Chelex 100, a commercially available resin containing iminodiacetic acid functional groups, which strongly bind transition metal ions via chelation [2]. The selectivity of Chelex 100 for transition metals over alkali and alkaline earth metals ensures that the major ions in natural waters (i.e. Na+, K+, Mg2+, Ca2+) do not interfere with the measurement of transition metals typically present in much lower concentrations (i.e. trace metals) [3]. Without the high degree of selectivity that Chelex 100 exhibits for trace metals, successful measurement of these analytes in awide variety of naturalwaterswould not be possible, due to competition for binding sites by major ions.