对氨基二甲基苯胺光度法测定废水中硫化物的不确定度评价

Determination of Sulfide in Waste Water by 4-Amino-Dimethyl-Aniline Spectrophotometry:Uncertainty Evaluation

用对氨基二甲基苯胺光度法测定了废水中的硫化物含量,通过对测定过程的系统分析得出测定结果的不确定度主要由硫化物标准使用液、标准曲线、分光光度计、水样用量和随机效应5个分量引入。利用数学模型逆推分析了标准使用液的不确定度来源,给出了不确定度来源的因果图。对各不确定度分量进行评定得知,标准使用液和随机效应引入的不确定度最大,而标准使用液的不确定度主要来源于滴定过程。计算得到了合成相对标准不确定度和扩展不确定度,水样中硫化物的测定结果为(0.74±0.02)mg/L(包含因子k′=2)。同时提出了降低不确定度的方法:提高分析操作的规范化程度、增加重复测定次数可减小测定的不确定度;使用自动电位滴定仪来判断终点或在惰性气体中进行滴定可减小由滴定过程引入的不确定度。

The content of sulfide in waste water was determined by 4-amino-dimethyl-aniline spectrophotometry. The uncertainty of measurement was mainly introduced from 5 component parts, which were standard solution, standard curve, spectrophotometer, volume of the compounded water sample and random effect. The uncertainty of standard solutions was analyzed by inverse deduction of the mathematical model. A cause and effect chart for an overall source of uncertainty of the sulfide standard solution mass concentration was plotted. Each component part of uncertainty was evaluated and quantified. It revealed that major part of uncertainty was contributed by random effect and standard solutions. The latter mainly originated from titration. Combined relative standard uncertainty and expanded uncertainty were calculated. The measurement result of sulfide in the water sample was expressed as （ 0. 74± 0. 02 ） mg/L, （ coverage factor k′ - 2 ）. Finally a method of reducing the uncertainty was put forward. The uncertainty could be greatly reduced by improving standardization of procedures for the operator or by repeating the determination more times. Taking potentiometric titration to estimate the end point of titration more accurately or conducting the titration in inert atmosphere were measures to reduce the uncertainty introduced during operation.