Effect of chloride ion on the cod determination with potassium dichromate

Abstract

The present work was undertaken to elucidate the effect of chloride ion on the COD determination with potassium dichromate. The COD value was determined by JIS method. Kraft pulp mill black liquor, its waste water effluent, municipal waste water influent, and its effluent were used as samples. The results are as follows; (1) The COD determination method with potassium dichromate as described in JIS was influenced by chloride ion. (2) The COD values of all given samples increased with the increment of the concentration of chloride ion. The extent of the increment of the COD value varied with the concentration of sample and species of samples. (3) In the presence of chloride ion, a linear relationship between the COD value and the dilution ratio of sample was not observed. (4) The increment of the COD value (ΔCOD) resulted by the oxidation of chloride ion increased with the decrement of the concentration of sample. (5) Mercuric sulfate could not suppress the oxidation of chloride ion in spite of its further addition, twice to three times as much as the quantity described in JIS. © 1975, The Japan Society for Analytical Chemistry. All rights reserved.