Abstract
The effect of chloride ion on the acidic COD determination with potassium permanganate was studied using semi-micro method which is adopted as the official method in the Environmental Quality Standards in Japan and is applied to water samples containing a large quantity of chloride ion such as sea water and estuarine water.
The blank tests were carried out by making produce the same amounts of silver chloride as in water samples in order to maintain the same condition as in the COD determination for water samples. The amounts of potassium permanganate consumed were kept constant at various concentrations of chloride ion by addition of the amount of silver sulphate equivalent to chloride ion in the solution.
In the presence of organic matter and chloride ion, the consumed amounts of potassium permanganate for all given samples increased linearly with the increment of the concentration of chloride ion at various levels of organic matter concentration in spite of addition of silver sulphate equivalent to chloride ion contained.
The degree of increment of the COD value varied with the kinds of organic matters contained in water samples. Furthermore, the effect of chloride ion in artificial sea water on the COD determination was higher than sodium chloride.
