铵离子对COD测定的干扰及干扰的消除方法

水样中只存在铵离子时对COD的测定几乎没有影响,而当铵离子与氯离子同时存在时,除了氯离子带来的干扰外,铵离子也会对COD的测定产生干扰。针对此现象,研究建立了加碱氮吹法,此法可有效去除COD测定中浓度小于1 000 mg/L铵离子的干扰,并确定了最佳除铵离子条件为过量加碱、600 m L/min的氮气流量和3 h的通气时间。通过7次平行测定含铵离子干扰物的水样,该方法的相对标准偏差为3.3%~6.5%,加标回收率为90.2%~97.0%,表明方法具有较好的精密度和准确度,能够较准确测定含有铵离子干扰水样的COD。

The Interference of Ammonium Ion on the Determination Result of COD and Method to Eliminate

Research shows that there is almost no interference on the determination result of COD when ammonium ion exists singly in water sample; but ammonium ion may disturb the determination result when ammonium ion and chloride ion exist in water sample at same time except the interference brought by chloride ion. In this study, we set up Alkali additon-nitrogen purge method which can remove the interference of ammonium ion (<1 000 mg/L)effectively, and the best condition of the method is defined. When we control ventilation time at 3 hours, nitrogen flow at 600 L/min and adding alkali excessively, the relative standard deviation of this method is 3.3%-6.5%(n=7) and the recovery of standard addition is 90.2%-97.0%. It shows that the new method applicating in the COD measurement disturbed by chloride ion and ammonium ion could acquire more accuracy result.