Protonation constants and association of polycarboxylic ligands with the major components of seawater

Apparent protonation constants, log beta (H*)(j), of 11 carboxylic acids we re determined potentiometrically ([H+]-glass electrode) in artificial seawa ter containing six of the major components (Na+, K+, Mg2+, Ca2+ Cl-, and SO 42-) at different salinities: S (parts per thousand) = 5, 15, 25, 35, 45. V alues of log beta (H*)(j) were fitted by the simple polynomial equation log beta (H*)(j) =log (T)beta (H)(j) + a(1)S(1/2) + a(2)S + a(3)S(3/2) (log (T )beta (H)(j) = protonation constants at infinite dilution; a(1), a(2), a(3) = empirical parameters), for mono-, di-, and tricarboxylates. For carboxyl ic anions with charge < -3, a better fit was obtained using the equation lo g <beta>(H*)(j) = log (T)beta (H)(j) + b(1)I b(0)z* log(1 + b(2)I) (b(0), b (1), b(2) = empirical parameters, z* = square sum of reactants minus square sum of products). The potentiometric data were also interpreted in terms o f complex formation between the cationic component of artificial seawater a nd the carboxylic anion (also partially protonated) using the single-salt a pproximation (the artificial seawater considered as a single salt with B1.1 17+ cation and A(1.117-) anion). Calculations were also performed, for comp arison, on potentiometric data for phenolic compounds (already published) t o obtain the formation constants of seasalt complexes. Generally, both empi rical parameters for dependence on ionic strength and complex formation, co nstants are dependent on the charge of the (poly)carboxylic anions. Some us eful stability-charge and stability-structure relationships are reported. T he interaction of carboxylic ligands with the major components of seawater is discussed in relation to speciation problems.