紫外荧光法检测饮用水中铀的影响因素与不确定度评价

Evaluation of influencing factors and uncertainty of detection of trace uranium in drinking water using ultraviolet fluorescence

目的分析影响紫外荧光法测量饮用水中铀准确性的因素、分析测量过程中不确定度,实现饮用水中铀的快速、准确测量。方法通过研究饮用水中不同酸度、不同Fe^(3+)含量和Mn^(2+)含量条件下对测量结果的影响,分析该方法的最佳测量条件。通过低中高3种浓度的加标样品研究标准品配制、样品前处理、测量等过程引入的误差,分析不确定度来源,进行不确定度合成。结果当水溶液pH=1~11时所绘制的标准曲线,其线性回归系数>0.995,符合仪器的线性测量范围。当pH为12左右时,其线性回归系数为0.761,不满足测量要求。当pH<3或pH>10时,荧光计数增加量低,或可导致测量误差增大。当Fe^(3+)含量≥15 mg/L时,测量值有很大偏差,严重影响测量结果。当Mn^(2+)含量≥1.6 mg/L时,样品产生白色沉淀,影响测量准确性。结果的合成相对标准不确定度分别为6.42×10^(-2)、4.48×10^(-2)、5.26×10^(-2)μg/L,扩展不确定度分别为0.03、0.06、0.12μg/L(k=2)。结论该分析方法测量饮用水中铀的最佳条件为待测样品pH值3~10,Fe^(3+)浓度应<15 mg/L,Mn^(2+)浓度≤1.6 mg/L。不确定度评价中重复测量误差和加入标准溶液体积是紫外荧光法测量水中铀不确定度的主要来源。

Objective To achieve rapid and accurate detection of trace uranium in drinking water by analyzing the factors influencing the accuracy of uranium measurement in drinking water using ultraviolet fluorescence method and by evaluating the uncertainty in measurement.Methods The influence of acidity,Fe^(3+)and Mn^(2+)contents on the analitical result were studied to optimize the measurement conditions.The accuracy of the measurement method was verified in 7 laboratories.By studying the errors introduced in the process of standard preparation,sample pretreatment and measurement,the sources of uncertainty were analyzed and the uncertainty was synthesized.Results At pH 1-11 in aqueous solution,the linear regression coefficient of the standard curve was greater than 0.995,which was in line with the linear measurement range of the instrument.At pH 12 or so,the linear regression coefficient was 0.761,which could not meet the measurement requirements.At pH<3 or pH>10,the increase in fluorescence count was lower,which might increase the measurement error.At Fe^(3+)concentration≥15mg/L,a large deviation occurred in measurement value that could affect seriously measurement result.At Mn^(2+)concentration≥1.6mg/L,the sample produced white precipitation,which could affect the measurement accuracy.Three spiked water samples with different concentrations were determined in 8 laboratories.Each water sample was measured six times in parallel.The relative standard uncertainty of the result were 6.42×10^(-2),4.48×10^(-2) and 5.26×10^(-2)μg/L,and the expanded uncertainties were 0.03,0.06 and 0.12μg/L(k=2),respectively.Conclusions The optimum conditions for the determination of uranium in water using this method pH were in samples 3-10,the concentration of Fe^(3+)less than 15 mg/L,and the concentration of Mn^(2+)less than or equal to 1.6 mg/L.The main sources of uncertainty in the measurement of uranium in water using ultraviolet fluorescence method arise from the repeated measurement error and the volume of added standard solution.