1993 Volume 44 Issue 4 Pages 119-134
The kinetics of competitive effects of side reactions for the complexation reaction between copper and the strong organic ligand isolated from seawater is examined with regard to other metals that were possibly present in the equilibrium systems and also a chelating agent, EDTA (ethylenediaminetetraacetic acid) that was added exogenously in the procedure developed by Midorikawa and Tanoue (1994). The kinetic problems in the ligand-exchange reaction of the strong ligand with EDTA is negligible because of quantitative removal of the alkaline earth metal ions in the pretreatment of seawater samples. It is found that the assumption for the concentration of copper-EDTA complex in the sample, introduced by Midorikawa and Tanoue (1994) in their equilibrium model, may lead to a conservative estimate of the conditional stability constant of the strong ligand, taking into account the kinetic reactivity of the strong ligand for copper complexation.
When trace metals other than copper are present, the model calculation demonstrates that these metal-competition effects involving the side reactions of EDTA finally lead to an overestimation of the conditional stability constant for the strong ligand. The magnitude of the overestimation is as small as the errors in its estimation based on the uncertainties of measurements. Possible metal competitions for the strong ligand may result in the conservative estimate of the total concentration of the strong ligand and would have no serious influence on the estimation of its conditional stability constant.
