M. Filella et Rm. Town, Heterogeneity and lability of Pb(II) complexation by humic substances: practical interpretation tools, FRESEN J AN, 370(4), 2001, pp. 413-418
The complexation of Pb(II) by natural organic matter (NOM) is better descri
bed by taking into account the dependence of the strength of binding on met
al loading conditions. The utility of a linear differential equilibrium fun
ction for interpretation of metal ion binding data is demonstrated. This ap
proach considers the binding intensity (log K*) as a function of metal ion
loading (theta = bound metal/binding site concentration). Three methods for
calculating this function are presented:
direct calculation from metal titration curves,
direct calculation from polarograms, and
compilation of data derived from interpretation of complexation in terms of
one- or two-binding sites (e.g. Scatchard analysis), i.e. Cc (complexation
capacity effective site concentration)-K pairs.
Heterogeneity also impacts on the apparent lability of complexes; complexes
formed at the lowest metal loadings are the least labile.