PhD Graduation

Location, date and time:

Location

Aula Wageningen University

Generaal Foulkesweg 1

Wageningen

Date

September 14, 2010

Duration

1:30 PM to 3:30 PM

This thesis deals with several aspects of the use of Diffusive Gradient in Thin film (DGT) and Diffusive Equilibriation in Thin film (DET) in dynamic metal speciation analysis. It has a clear focus on the properties of the diffusive gel layer, and their possible impact on metal speciation measurements in samples containing nanoparticulate and colloidal complexing agents.

The paramount feature of the DGT technique is the well-defined control over the diffusive layer thickness. DGT realizes this via the introduction of a hydrogel layer in which diffusion is the sole mode of transport for ions and complexes that are able to enter the gel phase. The rate of diffusive transport across the gel layer is then governed by the species mobility and the layer thickness, with the latter parameter being under full control of the analyst.

In order to maintain a limiting steady-state flux across the gel layer, it is backed by a strong cation exchange layer that acts as a perfect sink for metal ions. The most common set-up uses a Chelex-resin. Nowadays, DGT is being employed for systems that are increasingly complex, and sometimes largely uncharacterized. Although this creative branching opens up a lot of opportunities, it also introduces a host of potential complications that require dedicated solutions. Nevertheless, more detailed knowledge is required to address the pitfalls that are already present in the most straightforward application of DGT in aquatic systems. Here we do this to a significant extent by combining DGT with DET measurements on the same sample system, using exactly the same gel in each case, to fully utilize the complementary nature of the two techniques.

Promotor: Prof.dr. M.A. Cohen Stuart

Co-promotor: Prof.dr. H.P. van Leeuwen