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

Environmental Chemistry2014Vol. 12(2), pp. 112–122

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Abstract

Environmental context Dynamic speciation of an element in a natural medium is essential for understanding its availability. The technique of diffusion gradients in thin films (DGT) has become a widely used tool for in situ environmental studies, being applied to determine fluxes of metal cations, anions, organics and nanoparticles. The interpretation of the measurements with suitable physicochemical models gives valuable insights into the behaviour of the system. Abstract 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 DGT practitioner. Present limitations and challenges for future work in DGT interpretation are also discussed.

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Abstract

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