Abstract
In this study the BEST7 software was employed to quantify different classes of functional groups and to model the proton titration behavior of humic substances. To illustrate the process, the Suwannee River fulvic acid of the IHSS (International Humic Substances Society) was used. Five categories – two classes of phenolic groups (phenol and cathecol), two classes of carboxylic groups (benzoic and phtalic) and the combination between them (salicylic) - of oxygenated groups were considered as being responsible for the potentiometric behavior of the sample and were quantitatively determined. The most and the least abundant groups were cathecol (3.300 0.010 mmol g-1) and phenol (1.225 0.070 mmol g-1), respectively. The estimated equilibrium constants were also determined and were in good agreement with the literature values for phenol and cathecol groups and for benzoic, phtalic and salicylic acids. Distribution diagrams of the species were generated with the software SPE and SPEPLOT.
Highlights
Humic substances (HS) are environmentally significant because they control the pH balance, mobility of contaminants, nutrient bioavailability, mineral weathering, aggregation, sedimentation and metal transport both in aquatic and terrestrial systems [1,2,3]
The aim of this study is to develop a methodology using the software BEST7, SPE and SPEPLOT to quantify and to predict the speciation of reactive functional groups of any type of HS, as a function of pH
From the analytical data published on the International Humic Substances Society (IHSS) webpage, the presence of nitrogen in Suwannee River fulvic acid (SRFA) is less than 2%
Summary
Humic substances (HS) are environmentally significant because they control the pH balance, mobility of contaminants, nutrient bioavailability, mineral weathering, aggregation, sedimentation and metal transport both in aquatic and terrestrial systems [1,2,3]. The nature, size, molar mass, conformation and aggregation processes of HS are still poorly understood. Most HS researchers uphold the theory that they are macromolecular structures because their apparent molar masses can exceed 1,000,000 g mol-1 [4,5,6]. Two carboxylic groups alongside one another form a multidentate binding site for metals which gives rise to a much more stable complex than that formed by an isolated carboxylic group. A carboxylic can be alongside a phenolic group, or two phenolic groups can be located side by side. These combinations generate different kinds of linkages or interactions [16]
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