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Target measurement uncertainty as a tool for validation of uncertainties estimated by different approaches: determination of total hardness in drinking and natural waters

机译:目标测量不确定度作为验证通过不同方法估算的不确定性的工具:确定饮用水和天然水中的总硬度

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In this work, a procedure for total hardness determination in drinking and natural waters, expressed by the equivalent mass concentration of CaCO_3, γ_s, using an in-house complexometric titration with ethylenediaminetetraacetic acid based on standardized procedure was detailed. Compliance of the procedures requirements with legislation is discussed. Validation and quality control actions were implemented, and a limit of detection of 0.6 mg L~(-1) was determined fulfilling the target limit of detection of 15 mg L~(-1) imposed by specific legislation. Measurement precision was estimated under repeatability conditions, where relative standard deviations close to 1 % were estimated, and in within-laboratory reproducibility, where relative standard uncertainties of 4 % and 0.5 % were obtained for γ_s lower and higher than 100 mg L~(-1), respectively. The results were considered unbiased whenever recoveries were within the range 0.90-1.10, fulfilling the target trueness value stated as 10 % of parametric value. The performance of the measurement procedure was also assessed by proficiency testing and z scores less than 2 were obtained. Measurement uncertainty was estimated by a modeling approach, using the law of propagation of uncertainty for variables not independent, and by empirical ones, such as single-laboratory validation and quality control data and proficiency testing. Measurement uncertainty computed from each model was assessed by ξ score performance indicator showing a good estimated uncertainty (|ξ|<2). Finally, a way is proposed to assess the suitability of the combined uncertainty by the different models, comparing them to a target expanded measurement uncertainty within the analytical range, calculated from maximum decreed precision and trueness criteria since no target uncertainties were stated in the legislation.
机译:在这项工作中,详细介绍了在饮用水和天然水中总硬度测定的程序,该程序使用基于标准程序的乙二胺四乙酸的室内络合滴定法,以当量质量浓度的CaCO_3,γ_s表示。讨论了程序要求与法规的符合性。实施了验证和质量控制措施,确定了0.6 mg L〜(-1)的检出限,以符合特定法规所规定的15 mg L〜(-1)的目标检出限。在重复性条件下估计测量精度,其中相对标准偏差估计接近1%,在实验室内再现性下,对于低于和高于100 mg L〜(γ-s)的γ_s,获得相对标准不确定度分别为4%和0.5%。 1)。只要回收率在0.90-1.10的范围内,满足目标真实性值(表示为参数值的10%),就认为结果没有偏见。还通过能力测试评估了测量程序的性能,并获得了小于2的z得分。测量不确定度是通过一种建模方法来估计的,它使用不确定性对非独立变量的传播定律以及经验性变量(例如单实验室验证和质量控制数据以及能力验证)进行估计。由ξ得分性能指标评估从每个模型计算出的测量不确定度,该得分表现出良好的估计不确定度(|ξ| <2)。最后,提出了一种方法来评估不同模型对组合不确定性的适用性,将它们与分析范围内的目标扩展测量不确定性进行比较,该不确定性是根据最大法度精度和真实性标准计算得出的,因为立法中未规定目标不确定性。

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