Systematic variability in proton and copper(II) complexation by dissolved organic matter from surface freshwaters.

摘要

The reproducibility of potentiometric titrations using a copper (II) ion selective electrode increases directly as a function of dissolved organic matter (DOM) concentration, measured as dissolved organic carbon. Conditional stability parameters (Log(K₁), Log(K₂)), calculated from titration curves using a 2-ligand Langmuir Isotherm, are also dependent on DOM concentration explaining 20% to 60% of the variation reported for these parameters in the literature. The effect of DOM concentration on Cu 2+ complexation is greater for allochthonous DOM, which also exhibits higher charge density and higher affinity for Cu2+, than autochthonous DOM (p 0.05). The Cu2+ complexing properties of DOM collected from surface freshwaters depend primarily on allochthonous DOM and cumulative hydrologic residence time (p 0.05) by approximating exposure to transformation and fractionation processes. Comparison to experimental transformation and fractionation processes in micro-reactors suggests that photochemical decomposition, microbial decomposition, and adsorptive fractionation could contribute to the observed pattern of Cu2+ complexation.