Speciation of low molecular weight carboxylic ligands in natural fluids: protonation constants and association with major components of seawater of oxydiacetic and citric acids

The interaction of oxydiacetate and citrate with the major components of seawater has been studied potentiometrically, at 25 degrees C, in an artificial seawater (containing Na(+), K(+), Ca(2+), Mg(2+), Cl(-) and SO(4)(2-)) at different salinities (5-45 parts per thousand). Apparent protonation constants were calculated, from potentiometric data, and estimated, using an appropriate complex formation model. Formation constants of complexes formed by oxydiacetate and citrate and the cation of seawater (the inorganic content of seawater being considered as a single 1:1 salt) were determined. The single salt approximation for the major inorganic components of seawater, which is a good tool in estimating the mean strength of polyanion interaction in seawater, was applied. The comparison of experimental and estimated results showed that a suitable complexation model can be used with reasonable accuracy to predict acid-base properties of carboxylic ligands in seawater. (C) 1999 Elsevier Science B.V. All rights reserved.