In natural waters, trace metal ion speciation is often controlled by the kinetics of slow exchange reactions involving multidentate ligands, a.k.a. chelating agents. Conditions within natural media (pH, constituent ions, competing ligands, etc.) influence the rate and pathway of ligand exchange. Here, we examine the influence of calcium ions on the pathway and rate of a well-characterized disjunctive ligand exchange reaction between nickel(II) nitrilotriacetate (NiNTA) and trans-N,N’-cyclohexanediaminetetraacetic acid (CDTA). Systematic examination of reaction kinetics was facilitated by capillary electrophoresis separation. Initial rates and reaction order were compared to those in the absence of calcium ion. The presence of calcium ions does not shift the reaction pathway but reduces overall exchange rates and alters reaction order under the conditions studied. Kinetic modelling is used to support a proposed mechanism and determine rate constants.

Modeling the kinetics of trace metal ion speciation: The influence of calcium ion on disjunctive ligand exchange

253rd National Meeting (2017)

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