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Information Provided on Humic Substances by E4/E6 Ratios
Author(s) -
Chen Y.,
Senesi N.,
Schnitzer M.
Publication year - 1977
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1977.03615995004100020037x
Subject(s) - humic acid , chemistry , fulvic acid , aqueous solution , carbon fibers , dissolution , particle size , particle (ecology) , total organic carbon , inorganic chemistry , environmental chemistry , organic chemistry , materials science , fertilizer , oceanography , composite number , composite material , geology
The ratio of optical densities or absorbances of dilute, aqueous humic and fulvic acid solutions at 465 and 665 nm (E 4 /E 6 ) is widely used by soil scientists for the characterization of these materials. While it has been suggested that the E 4 /E 6 ratio is related to the degree of condensation of the aromatic carbon network, carbon content, and molecular weight of humic substances, little rigorous experimental evidence is available in the literature to confirm these hypotheses. The results of this investigation show that the E 4 /E 6 ratio of humic and fulvic acid is: (i) mainly governed by the particle size (or particle or molecular weight); (ii) affected by pH; (iii) correlated with the free radical concentration, contents of O, C, CO 2 H and total acidity in as far as these parameters are also functions of the particle size or particle or molecular weight; (iv) apparently not directly related to the relative concentration of condensed aromatic rings; (v) independent of humic acid and fulvic acid concentrations, at least in the 100–500 ppm range. Our data show, in agreement with M. M. Kononova (1966), that E 4 /E 6 ratios for humic and fulvic acids should be determined between pH 7 and 8. This can best be done by dissolving the humic material in 0.05 N NaHCO 3 solution at concentrations of 200–400 ppm.