STRUCTURAL INFORMATION OBTAINED FROM SPECTRAL-ANALYSIS (UV-VIS, IR, H-1-NMR) OF PARTICLE-SIZE FRACTIONS IN 2 HUMIC ACIDS

Humic acids (HAs) extracted from an Umbric Andosol (UA) and a Dystric Cambisol (DC) were fractionated into 7 fractions by successive gel per meation chromatography (GPC) and their fractions were studied by spect ral analysis. With increasing particle sizes, the absorption of methyl ene groups and amide of peptides increased in the IR spectra of both H As and that of carboxylic groups decreased in the IR spectra of UA, th e HA obtained from an Umkric Andosol. Based on the H-1 NMR data in UA, there was a significantly negative linear correlation (-0.950, p<0.00 1) between H-ar (delta 6.0-9.0 ppm) and H-c-o (delta 3.0-4.3 ppm). Suc h a negative linear correlation (-0.868, p<0.01) was also observed bet ween H-ar and H-beta (delta 0.9-1.6 ppm). In addition, with increasing particle sizes, the percentage of aromatic protons decreased (from 30 .6 to 4.2%). These results suggest that the increase in HA particle si zes depends on the length of aliphatic groups and the bond of methoxyl groups, and HAs were composed of HA molecules of homologous series. O n the other hand, in DC, HA obtained from Dystric Cambisol, no signifi cant relationships were observed between each type of protons and arom atic protons. It is suggested that a mixture of non-humic substances s meared the spectral data of DC.