Speciation of low molecular weight ligands in natural fluids: protonation constants and association of open chain polyamines with the major components of seawater

The interaction of five open chain polyamines (ethylenediamine (en), diethy lenetramine (dien), trietylenetetramine (trien), tetraethylenepentamine (te tren), spermine (sper)) with the major components of seawater was studied p otentiometrically at 25 degrees C, in an artificial seawater (containing Na +, R+, Mg2+, Ca2+, Cl- and SO42-) at different salinities (5-45 parts per t housand). Potentiometric data were interpreted in terms of both the apparen t protonation constants of polyamines and the formation constants of comple xes formed by unprotonated or protonated amines and the cation and the anio n of seawater (the inorganic content of seawater bring considered as a sing le 1:1 salt). Some empirical relationships, involving the polyammonium cati on charge and the ratio between N and C atoms in the amine, are reported. T hese relationships have quite a good predictive value. The association abil ity of seawater salt towards amines is quite significant: at pH 8.2 and 35 parts per thousand salinity formation percentages range between 50 and 80%. Speciation problems are discussed. (C) 2000 Elsevier Science B.V. All righ ts reserved.