Natural organic matter (NOM) such as humic substances found in soil, sediment and water has diverse mixture and molecular structural complexity. Among various functional groups, carboxylic acids and phenols are the most important ionizable sites present in HAs and are likely to determine many of the properties of proton and metal ion binding exerted by these materials in natural waters, soils and sediments. Determination of the surface density of acidic functional groups and the magnitude of pKa's of carboxylic and phenolic groups is a first step in characterizing acidity, ion exchange capacity, and charge accumulation properties in humic substances. In this research, potentiometric titration is used to determine the fundamental acidic properties of natural humic substances and model humic compounds selected to determine the role chemical structure plays in carboxyl and phenol dissociation. The model compounds are small molecules that have structural features common in natural humic substances such as carboxylic group and phenolic group. The Ka values of the model compounds can be evaluated accurately and precisely, thus useful to determine structural variations in dissociation. To carry out potentiometric titrations, a fully automated compact titrator (Mettler Toledo Compact Titrator G10S equipped with a pH electrode Mettler DG-115-SC) is being used.

Characterization of the acid-base properties of selected humic acids

254th National Meeting (2017)

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