The Oxidation Behavior of Various Organic Compounds on the Determination of Chemical-oxygen Demand by Means of Flow-injection Analysis with Acidic Permanganate

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Abstract
Forty-five organic compounds have been oxidized with an acidic permanganate solution under various oxidation conditions. In an attempt to determine the standard substance for chemical oxygen demand (COD), their oxidation behavior is analyzed in detail with respect to the reaction temperature and the reaction time by means of flow-injection analysis using ammonium iron(II) sulfate as the internal standard. The compounds used are classified into three groups according to the oxidation values obtained by the standard CODMn method. The results show that the compounds with oxidation values of more than 50% are easily oxidized with acidic permanganate, even under relatively mild conditions; those with oxidation values of 5–50% are severely influenced by the reaction temperature and the reaction time, and those with oxidation values of less than 5% are seldom oxidized at below 100 °C or for less than 30 min. As a standard substance for COD, it has been established that a mixture of the compounds has to be properly chosen from the aforementioned three groups according to the oxidation behavior of the water sample. The addition of silver nitrate to the oxidation system accelerates the oxidation reaction with acidic permanganate, whereas that of phosphoric acid suppresses the oxidation of organic compounds.