Effects of Lability of Metal Complex on Free Ion Measurement Using DMT

L.P. Weng, W.H. van Riemsdijk, E.J.M. Temminghoff

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14 Citations (Scopus)


Very low concentrations of free metal ion in natural samples can be measured using the Donnan membrane technique (DMT) based on ion transport kinetics. In this paper, the possible effects of slow dissociation of metal complexes on the interpretation of kinetic DMT are investigated both theoretically and experimentally. The expressions of the lability parameter, , were derived for DMT. Analysis of new experimental studies using synthetic solution containing NTA as the ligand and Cu2+ ions shows that when the ionic strength is low (=0.2 mM Ca(NO3)2) the dissociation rate of NTACu becomes the limiting step in Cu transport of the DMT measurement. In natural waters, dissolved organic matter (DOM) is the most important source of ligands that complex metals. By comparing the fraction of labile species measured using other dynamic sensors (DGT, GIME) in several freshwaters, it is concluded that in most waters ion transport in DMT is controlled by diffusion in the membrane. Only in very soft waters (
Original languageEnglish
Pages (from-to)2529-2534
JournalEnvironmental Science and Technology
Issue number7
Publication statusPublished - 2010


  • donnan membrane technique
  • soil solution
  • in-situ
  • dynamic speciation
  • trace-metals
  • copper
  • waters
  • dissociation
  • equilibrium
  • dialysis


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