Characterization of humic substances and polyacrylic acid: A high precision conductimetry study

The size and the charge of humic substances are key parameters to access their transport properties and their potential ability of complexation in the soil. The purpose of this paper is to show that high precision conductimetry coupled to a suitable transport theory give access, at various pH, to the size and charge of reference humic and fulvic acids, reference natural organic matter (NOM) and polyacrylic acids. The obtained results are compared and confirmed by two independant techniques: atomic force microscopy and dynamic light scattering.Whatever their geological origins, the studied humic acids (HA) seem to have the same charge and also the same diameter of approximately 2 nm. The pH has an effect on the effective charge of these environmental colloids but not on their size. Polyacrylic acid (5100 g/mol) can be considered as a good analogue of these humic acids concerning size and charge in solution. In comparison to these colloids, reference fulvic acid and NOM are smaller with a diameter around 1–1.5 nm and also have a lower effective charge.