CHARACTERIZATION OF HUMIC ACIDS FROM DIFFERENT ENVIRONMENTS

Abstract: The chemical composition and structure of four humic acids (HAs) from different origins were investigated by term of elemental analysis, Fourier transform infrared (FT-IR) spectrometry, and solid-state CP-MAS 13C nuclear magnetic resonance spectroscopy (13C NMR). The results showed that four HAs have similar chemical composition and structural properties, but the details were very different. (1) H/C, O/C, and C/N atomic ratios are different for four HAs, suggested that their differences in chemical composition and structure; (2) FT-IR spectra indicated that peat and paddy HAs contain more aliphatic group and less carboxylic/carbonyl groups than pond and river HAs; (3) distinct structural differences existing among 4 HAs were indicated by CP-MAS 13C NMR data. The relative content of aliphatic group was the highest in Paddy HA, and decreased from peat HA, pond HA to river HA. On the contrary, increasing contents of aromatic groups varied from river HA, pond HA, peat HA to paddy HA. Moreover, Oxygen-containing groups such as methoxyl, carbohydrates, carboxylic/carbonyl, were also very different among four HAs