As an analytical method for determining aromatic constituents of humic substances, as possibly the main precursors of organic chlorine compounds, the premethylation-KMnO
4 oxidation method was investigated. The humic substances were reagent grade humic acid, humic acid in the moat, humic acid and fulvic acid in a leaf mold, and fulvic acid in a treated sewage. All were extracted and refined prior to analysis.
When the humic substances were oxidized directly with KMnO
4, small amounts of aromatic compounds possessing methoxyl groups were obtained from methylated samples of oxidation products. Decomposition of aromatic rings possessing hydroxyl groups may be the reason for this. However, when hydroxyl and carboxyl groups of the humic substances were methylated before KMnO
4 oxidation, large amounts of aromatic compounds possessing methoxyl groups were obtained, and it was thus possible to clarify the characteristics of the humic substances.
It is evident from the present results that the premethylation-KMnO
4 oxidation method is useful for accurately determing the aromatic constituents of humic substances otherwise not possible by the direct KMnO
4 oxidation method.
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