Speciation of polyelectrolytes in natural fluids: Protonation and interaction of polymethacrylates with major components of seawater

Acid–base properties of two sodium polymethacrylates (W=4000 and 5400 Da) were studied potentiometrically in aqueous solution at 25 °C. Measurements were made in different salt solutions: LiCl 0.1–1.5, NaCl 0.1–2, KCl 0.1–2, Et4NI 0.1–0.75 mol l−1, and in artificial seawater in the salinity range 10≤S≤45. Protonation data were analysed by two different models and the dependence of the relative parameters on ionic strength were calculated. Measurements performed in interacting media (alkali metal chlorides and artificial seawater) were interpreted in terms of complex formation, and the relative formation parameters are reported. Previous data on the interaction of a higher molecular weight (W=230 000 Da) polymethacrylic acid with alkaline metal cations and Ca2+ were reanalysed in the light of correct procedure which takes the effective polyanion charge into account. The speciation of methacrylates, in aqueous solutions containing the major constituents of natural fluids, is discussed in relation to the various parameters that influence the stability of different species formed.