A unified physicochemical description of the protonation and metal ion complexation equilibria of natural organic acids (humic and fulvic acids). 2. Influence of polyelectrolyte properties and functional group heterogeneity on the protonation equilibria of fulvic acid

Adsorption of fulvic acid on goethite

“…Similar charging behavior of FA was found in several studies (Ephraim et al, 1986;Christensen et al, 1998). The data show an increase in negative charge of the FA with increasing pH.…”

Competition effects in cation binding to humic acid: Conditional affinity spectra for fixed total metal concentration conditions

“…Metal ions release protons from acidic groups too weak to be ionized otherwise, as already reported by Ephraim et al (Ephraim et al, 1986; The distribution of affinities resulting from the fitted NICA parameters is depicted in Fig.1b. Since NICA reduces to a Langmuir-Freundlich isotherm when only one ion is present in the system, the distribution depicted in Fig.…”

“…Among them, let us discuss the arrangement of acid base titrations performed in the presence of a constant total metal concentration, which is varied over successive experiments (Ephraim et al, 1986;van Dijk, 1971). In addition to its experimental simplicity, this procedure allows the indirect assessment of the binding characteristic of the competing cations by means of their effect on the proton binding.…”

Determination of Dissociation Constants of Some Novel Tetrahydropyrimidine Derivatives in Mixed Organic-Water System by Simple pH Measurement

“…However, considering the 2 H pK values of these two (PAB-108 and PAB-110) compounds indicates the higher acidity of PAB-108 which may be due to the presence of methoxy group. Similar characteristic behavior was also reported earlier [24]. Alteration of hydroxy group with any other functional group…”