试验表明用重铬酸钾法测定废水的COD值时加入硫酸汞作掩蔽剂对废水中共存有高浓度氯离子和溴离子的干扰不能消除,特别是对溴离子几乎没有掩蔽作用。提出根据废水中氯离子和溴离子的实际含量,定量加入硝酸银作掩蔽剂可同时消除氯离子和溴离子的干扰。COD的回收率在102%~106%之间。

It was found that elimination of interference of Cl- by masking with mercuric sulfate as stated in the titrimetric determination of COD in waste water with K2Cr2O7 solution as titrant was not very effective for high concentration of Cl- ion and that it was even invalid for masking the co-existing Br- ion. It was proposed to use silver nitrate instead of mercuric sulfate to mask both the Cl- and Br- simultaneously. It was shown that if an amount of AgNO3 calculated stoichiometrically on the base of the amount of Cl- and Br- ion present was added as masking agent, the interferences were eliminated effectively, giving values of recovery ranged from 102% to 106%.