A direct potentiometric titration study of the dissociation of humic acid with selectively blocked functional groups

Abstract

Abstract:A direct potentiometric titration method was applied to commercial and soil humic acids in order to determine their carboxyl and phenol group concentrations and apparent and intrinsic pK. In that context, acid-base properties of humic acids are interpreted by selective blocking of carboxylic and phenolic groups by esterification and acetylation. Differences in underivatized and derivatized HA's acid-base properties are ascribed to carboxyl and phenol groups influence on total humic acidity. Potentiometric data were treated with the modified Henderson-Hasselbalch equation. Infra red results, the acidic group contents and the average values of apparent and intrinsic pK for underivatized and derivatized HAs confirmed the selectivity of esterification derivatization method. After blocking of the functional groups, the values of acidic group contents decreased, while the value of apparent pK increased after derivatization. Phenol groups cannot be specifically identified by the acetylation method, due to low selectivity of the acetylation method.

Characterization of dissolved organic matter from a restored urban marsh and its role in the mobilization of trace metals

“…Metal complexation measurements were performed via voltammetry (Rozan et al, 1999;Kovaleva, 2004;Andjelkovic, 2006). An AIS Model DLK-100A Electrochemical Analyzer Rev 3.3 was used to the determine complexation capacity of metals with DOM.…”

“…(1) (Chau and Lum-Shue-Chan, 1974;Mantoura et al, 1978;Luther, 2001;Hansell and Carlson, 2002;Weng et al, 2002;Baken et al, 2011;Mostofa et al, 2013). Some functional groups including carboxylic, phenolic, nitrogen, and sulfur containing groups, have high affinities for metal ions, creating stable complexes of varying complexing strengths (K c ) (Ephraim and Marinsky, 1986;Abate and Masini, 2002;Hansell and Carlson, 2002;Andjelkovic, 2006;Fellman et al, 2008). These interactions will affect the transport and ultimate fate of trace metals (TM).…”

Equilibrium studies of binding of cationic surfactants to sodium humate

“…But the total amounts of the bound surfactant are different from those quoted from [23]. According to a recent study, however, the concentration of the -COOH groups of the Aldrich HA is 7.10 mmol/g C [26] which is reasonably close to our value of 8.36 mmol/g C and compares also well to the above mentioned proton binding capacity of the HS carboxyl group 8.5±0.9 meq/g C [8]. Both of these data indicate that the negative charges are compensated by the cationic CPC.…”

Kinetics of the sulfate radical‐mediated photo‐oxidation of humic substances

“…Figure 4 shows the dependence of K 4 on the ionic strength, I , obtained with different added electrolytes both at pH 4.6, where the carboxylic groups of AHA should be partially protonated, and at pH 3.0, where these groups should be mainly protonated [18]. The results obtained with the addition of Mg(ClO 4 ) 2 and NaClO 4 fall in the same straight line, which indicates that the ionic strength and not the cation valence is responsible for this behavior.…”