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The paper presents the characterization of the Chelex-based resin hydrogels used as a passive sampling technique of diffusive gradients in thin film (DGT) to determine the binding profiles of iron in aquatic environments. The non-destructive photothermal beam deflection spectrometry is employed to carry out the analysis. Under non-advective conditions, gels’ capacity and optimal experimental parameters for depth profiling have been established. Depth profiles reveal a layer-by-layer interaction between dissolved iron and resin binding sites. The obtained accuracy of the measurements when applied for iron determination in natural waters is obtained as 100 ± 5 % of the nominal concentration, whereas the precision under 5 % demonstrates good repeatability and reproducibility of the measurements