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Humic acids. Analytical study of humic acids

Humic acids (HA) -is a mixture of weak organic acids of the aliphatic and aromatic series that are insoluble in water in a neutral and acidic medium, but are soluble in alkali solutions. HA consist of that fraction of humic substances that precipitates from alkaline aqueous solutions when the pH is lower than 2. HA are considered as flexible linear polymers with cross-links that exist in the form of random coils. On average, 35% of the mass of HA is represented by aromatic radicals, while the remainder is in the form of aliphatic chains. The molecular weight of HA is in the range from 10,000 to 100,000 D. The GK readily forms salts with inorganic trace elements. Analysis of extracts extracted from natural HA showed the presence of more than 60 different trace elements bound to forms that can be used by various plant and living organisms.

Analytical study of humic acids has more than 200 years of history, but the most important issues of their origin and structure have not been solved so far. The fact is that the synthesis of high-molecular organic compounds in living organisms is carried out with the help of a genetic code and leads to structures that can be identified as individual compounds. Synthesis of humic acids is by natural selectionstructures capable of acquiring stability in the root layers of the soil and creating the necessary ecological conditions for the growth and development of plants and soil biota. An important role in optimizing the structure of HA is played by feedback with microorganisms. The complexity and multifactority of the mechanisms of formation of humic acids determines the diversity and high polydispersity of molecular structures. Therefore, all attempts to present the structural formula of humic acid (for example, the structure in Fig. 2) allow us to speak only of more or less successful models.

More complete information on the fragmentary composition of humic acids can be obtained using data from 13 C NMR spectroscopy . The most interesting in this area are the work of prof. G.A. Calabina [2]. G.A. Kalabin, together with us, carried out a comparative analysis of humic acids isolated from leonardite, which allowed us to justify the choice of the deposit for the production of high quality humates. The data presented in Table 2 show that the humic acids of this deposit are most saturated with oxygen-containing functional groups that determine the biological activity of humates (ketones, carboxyls, quinones, phenolic hydroxyls and esters).

table 2

Comparative analysis of structural parameters of humic acids from leonardite

Source of humic acids

C distribution by different functional groups,%

C = O



Carboxyls and quinones

From ap- O

Phenols and esters of the aromatic nucleus

With para -O

Ethers of aliphatic chains

Cherkassy deposit















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