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(70-38) In situ measurements of transfer kinetics and labilities of metal complexes in synthetic solutions using DGT. Scally, Shaun*,1, Davison, William1, Zhang, Hao1, 1 Lancaster University, Lancaster, UK ABSTRACT- The distribution of metal complexes in most natural waters controls the chemistry. To understand fully the availability of metals to biota, it is necessary to know the dissociation kinetics of the complexes. The technique of diffusive gradients in thin films (DGT) has been used to determine kinetic parameters relating to the lability of the metal complexes and their dissociation rate. Experiments were carried out in synthetic solutions containing either copper, cadmium, cobalt, or nickel, plus the complexing ligand nitrilotriacetic acid (NTA). They were designed to distinguish between labile (fast dissociation) and partially labile (slower dissociation) complexes. Because the dissociation rate constant for a particular complex depends on its stability constant and the metal's rate constant for water exchange, it was expected that Ni-NTA would be slowly labile, because Ni has a much slower rate of water exchange than Cu, Co, or Cd. Rate expressions were derived to relate the transfer kinetics to the effective measurement time of DGT. The model fits to the DGT measurements resulted in a dissociation rate constant, k, of 7.6-10.2 x 10-5 s-1 for Ni-NTA. The other complexes studied, Cu-NTA, Cd-NTA, and Co-NTA were found to be fully labile. Minimum values of the rate constants were estimated. All the results agreed well with the constants published in literature. This work has confirmed the theory of DGT for measuring labile metal complexes. Because of its simplicity and freedom from interferences, DGT can be deployed in-situ. Resulting measurements of kinetic parameters of labile complexes will advance our understanding of bioavailability of metals in waters, soils and sediments. Key words: DGT, Lability, kinetics, bioavailability |
