The interaction of amino acids with the major constituents of natural waters at different ionic strengths

The interaction of amino acids with the major constituents of natural water s has been studied potentiometrically by determining protonation constants at different ionic strengths (e.g., I less than or equal to 5.6 mol (kg H2O )(-1) (NaCl)) and in artificial seawater (containing Na+, K+, Ca2+, Mg2+, C l- and SO42-) at different salinities. For glycine determinations in mixed NaCl-MgCl2 electrolyte solutions were also performed. The data included in this work, together with some already published, make it possible to calcul ate parameters for dependence on ionic strength using different models, i.e . an extended Debye-Huckel type equation and Pitzer equations. The results can be interpreted both in terms of specific interaction and in terms of co mplex formation. The formation constants of Mg2+-glycine complexes have bee n calculated from protonation data in mixed Na+-Mg2+ solutions at high ioni c strength: a simple method for taking into account the different compositi on, at constant ionic strength, is reported. The overall complexing ability of major seawater components towards amino acids has been calculated from potentiometric data in artificial seawater using the single salt approximat ion. The relevance of the data reported in this work is discussed in connec tion with speciation problems. Particular attention has been paid to findin g some useful predictive relationships. (C) 2000 Published by Elsevier Scie nce B.V.