M. Kawahigashi et al., STRUCTURAL INFORMATION OBTAINED FROM SPECTRAL-ANALYSIS (UV-VIS, IR, H-1-NMR) OF PARTICLE-SIZE FRACTIONS IN 2 HUMIC ACIDS, Soil Science and Plant Nutrition, 42(2), 1996, pp. 355-360
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.