It has been believed that regenerated humic acids have carboxylic and phenolic hydroxy groups.
In the present paper, the experimental results to establish the best method for the quantitative determination of these acid groups were reported. The results obtained were the following:
(1) The potentiometric titration in nonaqueous solvents could be successfully applied to the determination of the carboxylic and phenolic hydroxy groups in the regenerated humic acids.
(2) Two kinds of the solvent, dimethylformamide and dimethylsulfoxide, were used, and it was found that dimethylsulfoxide was superior to dimethylformamide in respect of the dissolving ability of these solvents to the humic acids.
(3) As the titrants, the following standard solutions were used:
1) N/10-Benzene-methanol solution of lithium methoxide.
2) N/10-Benzene-methanol solution of sodium methoxide.
3) N/10-Benzene-methanol solution of potassium methoxide.
4) N/10-Dimethylformamide solution of sodium amino-ethoxide.
5) N/10-Dimethylsulfoxide solution of sodium amino-ethoxide.
6) N/10-Ethylenediamine solution of sodium amino-ethoxide.
7) N/10-Benzene-methanol solution of
n-butyl-triethylammonium hydroxide.
In these titrants, lithium methoxide was the best reagent which gave the least neutrarization equivalent of the humic acids.
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