Abstract
The chemical composition and structure of humic substances were established based on spectroscopic studies (EDXS, SRATR FTIR, and 13C NMR). Humic acids were isolated from different matrices such as soils, compost, lignite, and commercial lignohumate. The btained results showed the highest content of aromatic groups in lignite and humic acids of Chernozem. The aromaticity degree (a) calculated from 13C NMR spectroscopy data decreased in the following order: lignite > Chernozems > lignohumate > Luvisols > compost > Cambisols. Infrared spectroscopy detected bands indicative of aliphatic groups (C–H at 2925 cm−1); aromatic groups (C=C at 1620 cm−1); phenolic groups (at 1404–1419 cm−1); and carboxyl and carbonyl groups (at 1225–1223 cm−1) in all studied humic acid samples. The main differences were found in the fingerprint region of 1700–1000 cm−1. The reactivity of humic acids given by the O/R ratio showed that the highest amount of n-alkyl groups were in the lignohumate samples. EDX spectroscopy indicated elements occurring in situ. Soil humic acids contained Fe, Cu, Zn, Ti, Ca, K, S, P, Si, and Br.
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