Speciation of organic matter in natural waters—interaction of polyacrylates and polymethacrylates with major cation components of seawater

The speciation of some high molecular weight polycarboxylates was studied in different ionic media. Polyacrylates here investigated (W=2.0, 5.1 and 20.0 kDa) form weak species with alkali metal cations (K=102 mol l−1, t=25 °C, I=0 mol l−1) and quite stable complexes with alkaline earth metal cations (K>106 mol l−1, t=25 °C, I=0 mol l−1). Results are reported from experiments performed in a multicomponent electrolyte solution simulating the major composition of seawater (artificial seawater). Protonation constants in this medium are expressed as a polynomial function of S1/2 (S=salinity) and the sharp lowering with respect to values obtained in non-interacting aqueous tetraalkylammonium salts can be ascribed to the formation of alkali and alkaline earth cation complexes. A simplified approach, according to which the seawater salt is considered as a single 1:1 salt, was used to describe the total interacting ability of the major components of seawater towards polyacrylates. Protonation and complex formation data are reported as a function of the degree of proton dissociation and of the molecular weight: empirical equations to take into account these functions are also given.