title: Conditional affinity spectra of Pb2+-humic acid complexation from data obtained with AGNES.
abstract: The new electroanalytical technique AGNES (Absence of Gradients and Nernstian Equilibrium Stripping) has been applied to follow Pb2+ complexation to Purified Aldrich Humic Acid. A refined methodology of AGNES, allowing considerably larger gains, reached free metal ion concentrations down to subnanomolar values in a reasonable deposition time due to the lability and mobility of these complexes. Further insights into the meaning of the binding data, fitted to a NICA (Non Ideal Competitive Adsorption) isotherm, can be obtained with the concept of conditional affinity spectrum (CAS). For this purpose, we present the analytical expression for the CAS of NICA isotherm and show the CAS distributions for the Pb binding at fixed pH. Results reveal that the underlying spectra of each elementary distribution of the bimodal NICA evolve with pH yielding different overlapping and nonsymmetrical distributions. A non-negligible occupation of phenolic and carboxylic sites by Pb2+ takes place in the range of 4 < pH < 9.
authors.affiliation: Departament de Química, Universitat de Lleida, Rovira Roure 191, 25198 Lleida, Spain.
authors.forename: Jaume
authors.initials: J
authors.lastname: Puy
authors.forename: Josep
authors.initials: J
authors.lastname: Galceran
authors.forename: César
authors.initials: C
authors.lastname: Huidobro
authors.forename: Encarnació
authors.initials: E
authors.lastname: Companys
authors.forename: Núria
authors.initials: N
authors.lastname: Samper
authors.forename: Josep Lluís
authors.initials: JL
authors.lastname: Garcés
authors.forename: Francesc
authors.initials: F
authors.lastname: Mas
mesh_terms: D000327:Adsorption; D002264:Carboxylic Acids / Q000032:analysis; D002623:Chemistry Techniques, Analytical / Q000379:methods*; D006812:Humic Substances / Q000032:analysis*; D006863:Hydrogen-Ion Concentration; D007854:Lead / Q000737:chemistry*; D010636:Phenols / Q000032:analysis; D011522:Protons; D013057:Spectrum Analysis / Q000379:methods*; D013696:Temperature
chemical_list: D002264:Carboxylic Acids; D006812:Humic Substances; D010636:Phenols; D011522:Protons; D007854:Lead