Acid–base behaviour of a commercial sodiumalginate extracted from brown seaweed (Macrocystis pyrifera) has been investigated at different ionic strengths (0.1≤I/mol l−1≤1.0) and in different supporting electrolytes (Et4NI, NaCl, KCl, LiCl, NaCl+MgCl2), with the aim of examining the influence of ionic medium on the protonbinding capacity and of quantifying the strength of interaction with light metal ions in the perspective of speciationstudies in natural aqueous systems. Potentiometric ([H+]- glass electrode) and titration calorimetric data were expressedas a function of the dissociation degree (α) using different models (Henderson–Hasselbalch modified, Högfeldt three parameters and linear equations). The dependence on ionic strength of the protonation constants was taken into account by a modified specific interaction theorymodel. Differences among different media were explained in terms of the interaction between polyanion and metal cations of the supporting electrolytes. Quantitative information on the proton-binding capacity, together with the stabilities of different species formed, is reported. Protonationthermodynamic parameters, at α=0.5, are log KH= 3.686±0.005, ΔG0=−21.04±0.03 kJ mol−1, ΔH0=4.8±0.2 kJ mol−1 and TΔS0=35.7±0.3 kJ mol−1, at infinite dilution. Protonation enthalpies indicate that the main contribution to proton binding arises from the entropy term. A strict correlation between ΔG and TΔS was found, TΔS=−9.5–1.73 ΔG. Results are reported in light of building up a chemical complexation model of general validity to explain the binding ability of naturally occurring polycarboxylate polymers and biopolymers. Speciation profiles of alginate in the presence of sodium and magnesium ions, naturally occurring cations in natural waters, are also reported.
|Numero di pagine||10|
|Rivista||Analytical and Bioanalytical Chemistry|
|Stato di pubblicazione||Published - 2005|
All Science Journal Classification (ASJC) codes
- Analytical Chemistry