Interpretation of diffusion gradients in thin films (DGT) measurements: a systematic approach

Gaining insight into the physicochemical processes integrated in a DGT (diffusion gradients in thin films) measurement and combining them in a model can assist in retrieving fundamental information, both qualitative and quantitative, on the probed system. New experiments (such as varying the thicknesses of the gel or the resin layer) and their mathematical treatment to extract meaningful parameters have been suggested from theoretical considerations. The concept of lability degree is useful in describing an interpretation of the DGT concentration as the summation of the free metal concentration plus the labile fraction of all complexes multiplied by a ratio of diffusion coefficients. In some cases, the lability degree can be directly estimated with specific measurements and a very simple expression. We review the current status of these interpretations, including numerical simulations, with special focus on analytical expressions, because they can be more accessible to the standard DGTpractitioner. Present limitations and challenges for future work in DGT interpretation are also discussed.