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 se awater has been studied potentiometrically, at 25 degrees C, in an artifici al seawater (containing Na+, K+, Ca2+, Mg2+, Cl- and SO42-) at different sa linities (5-45 parts per thousand). Apparent protonation constants were cal culated, from potentiometric data, and estimated, using an appropriate comp lex formation model. Formation constants of complexes formed by oxydiacetat e 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 ap proximation 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 t hat a suitable complexation model can be used with reasonable accuracy to p redict acid-base properties of carboxylic ligands in seawater. (C) 1999 Els evier Science B.V. All rights reserved.