HA-C has a greater aliphatic character, is less unsaturated, has less acidic functional groups content and has less charge development than the other HA analyzed.
Compost application as an organic amendment modifies, in some way, the chemical and physicochemical characteristics of HA extracted after 9 months of compost use. This behavior suggests the interaction between the native HA and “HA-like substances” present in the composted materials.
Potentiometric titration and the first derivative of −Q versus pH curves can be used to determine proton-affinity distribution and the chemical heterogeneity of the HA as well as the average pKapp and buffer capacity in a wide range of pH. With this simple methodology it is possible to separate in three domains the acidic functional groups of the macromolecule.
Differential scanning potentiometry allows determination of the pKapp values in a narrower range of pH than potentiometric titrations and is another simple methodology to study acid–base behavior of HA.
DSP allows us to determine seven different pKapp values for HA-S and HA-E and four different pKapp for HA-C. Each one of these values corresponds to known acidic groups that can be present in the macromolecule of HA.