改进的重铬酸盐法测定水和废水中化学需氧量

Modification for the Method of Dichromate Titrimetric Determination of Chemical Oxygen Demand in Water and Wastewater

对重铬酸盐法测定水和废水中化学需氧量的国家标准方法作了改进。改进方法较原方法的取样量由20.00mL减少为10.00mL,氯离子掩蔽剂硫酸汞由固体改为溶液;改进方法受氯离子干扰的程度与国标方法相似,当氯离子质量浓度小于1 000mg·L-1时对测定结果无影响。改进方法的检出限为3 mg·L-1,对标准物质和标准溶液进行测定,测定结果的相对误差在0.96%~2.70%之间,标准偏差在0.80~5.6 mg·L-1之间,相对标准偏差（n=6）在0.80%~5.9%之间。方法应用于水样的测定,测定值与国标法测定值相符,测定值的标准偏差在0.94~20.5mg·L-1之间,相对标准偏差（n=6）在0.53%~11%之间。

A modification for the GB method of dichromate titrimetric determination of chemical oxygen demand in water and wastewater was proposed. As compared with the original method, the sampling volume was reduced from 20. 00 mL to 10. 00 mL, and the masking reagent for chloride ion was changed from solid mercury sulfate to mercury sulfate solutiorL The improved method was similar to the original method for interference by chloride ion, and it was shown that no interference was observed when mass concentration of chloride ion was under 1 000 mg · L-1. Detection limit of the method found was 3 mg · L-1. The proposed method was applied to the analysis of standard materials and standard solutions, giving values of relative errors, standard deviations and RSDrs （n=6） in the ranges of 0. 96%-2. 70%, 0. 80-5. 6 mg · L -1 and 0. 80%-5. 9%, respectively. The proposed method was applied to the analysis of water samples, giving results in consistency with those obtained by the GB method with values of relative errors, standard deviations and RSD＇s （n=6） in the ranges of 0.94-20. 5 mg · L 1 and 0. 53%-11%, respectively.