Assessment of trace metal binding kinetics in the resin phase of DGT devices 1 2

13 The dynamic technique of diffusive gradients in thin films (DGT), that measures metal 14 speciation in situ, has found wide environmental application. Simple interpretation of the 15 metal accumulation in terms of a solution concentration has assumed that trace metals do 16 not penetrate beyond the surface of the binding layer, but penetration, although 17 theoretically discussed has not yet been directly measured. Multiple binding layers were 18 used to enable analysis of different depths of a DGT binding phase (Chelex-100 or 19 iminodiacetate resins). In simple metal solution (no ligand) at pH 7, metal penetration to 20 the back layer was low and similar for all metals. However, at lower pH up to 42% of an 21 individual metal accumulated in the back resin layer. This was most noticeable for Mn at 22 pH 4 and 5, but Cd and Co were also affected at pH 4. These results were consistent with 23 rate limited binding, particularly for Mn. A kinetic model successfully fitted the data and 24 Published in Analytica Chimica Acta 2012, vol 717, p 145-150 10.1016/j.aca.2011.12.043 reprints also to [email protected]