水质COD测定方法的改进研究

国标GB 11914–1989测定水质COD的方法存在分析时间长、工作量大、能耗高,毒性大,且易造成二次污染的缺点,因此在国家标准的基础上对各实验条件进行优化改进。针对国标方法中的溶液酸体系、回流时间、催化剂、氧化剂4个因素,设计了三因素三水平和一因素两水平的混合正交实验方案来研究改进COD的测定方法。结果表明,当氧化剂为重铬酸钾,回流时间为40 min,硫酸与磷酸的体积比为3∶1,催化剂为硫酸银–硫酸铜(质量比为1∶1)时即为测定水质COD的最优条件。改进后的方法对水样COD测定结果的相对标准偏差为1.79%(n=5),对COD标准物质测定结果的相对误差为–0.26%。改进后的方法准确度高、试剂能耗成本降低、分析时间缩短三分之二。

Determination Method Optimization of Chemical Oxygen Demand(COD) of Water Quality

The national standard GB 11914–1989 for determination of water quality COD had disadvantages such as time consuming,high labor intensity,high energy consumption,heavy toxicity,and easy to cause secondary pollution, so the experimental conditions on the basis of the original national standard were optimized and improved. According to the national standard method,oxidant,ratio of concentrated acid,refluxing time and catalyst were chosed to design an orthogonal experiment. The mixed orthogonal experiment of three factors three levels and one factor two level was used to improve the determination methods of COD. Results of optimum conditions for determining COD were as follows:the oxidant was potassium dichromate,refluxing time was 40 minutes,volume ratio of sulfuric acid and phosphoric acid was 3∶1,catalyst was silver–copper sulfate(1∶1). The relative standard deviation of COD determination results was 1.79%(n=5), and the relative error for determination result of COD standard substance was–0.26%. The improved method for determining COD was accurate,has less reagent and energy cost with the analysis time shorten two-thirds.