Humic acids were fractionated using universal buffer solutions in the range of pH values 2-12. The methods of dynamic light scattering and gel-permeation chromatography were used to investigate the molecular organization of humic acids in eluates. The obtained results were supplemented by ultraviolet/visible spectrometry, measurement of the zeta potential, conductivity and pH values. Fractionated humic acids had the supramolecular character and their molecular organization was strongly affected by pH value of surrounding medium. Observed changes in the secondary structure of humic acids were connected with the changes in colloidal stability, particle size distribution, and polydispersity.Keywords: Humic substances, molecular arrangement, conformation, particle size, zeta potential
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