火焰原子吸收光谱法测定工作场所空气中镉及其化合物含量的不确定度评定

目的]探讨火焰原子吸收光谱法测定工作场所空气中镉及其化合物含量的不确定度评定方法。方法]依据国家职业卫生标准GBZ/T 160.5-2004和JJF 1059.1-2012的原理和方法,对不确定度的分量进行计算。结果]采集75 L和120 L标准采样体积引入的相对不确定度分别为0.008 4、0.004 8,标准溶液及配制过程引入的不确定度为0.006 6,标准曲线拟合引入的相对不确定度为0.025 8,样品制备过程引入的相对不确定度为0.030 0,样品重复测定引入的相对不确定度为0.001 5。合成相对标准不确定度为0.041 9,测定工作场所空气中镉及其化合物浓度为0.067 mg/m^3,扩展不确定度为0.005 mg/m^3(k=2)。样品溶液制备过程、拟合标准曲线和标准采样体积是本方法不确定度的主要来源,其他分量相对很小。样品溶液制备过程中样品消解过程引入的不确定度对合成不确定度的贡献最大。结论]在试验中,要注意减少样品前处理损失,选择高纯度标准液、标准物,加强前处理和标准曲线拟合等步骤的质量控制,减少测量结果的不确定度,保证试验数据的准确性、可靠性。

Uncertainty evaluation of method for determining cadmium and its compounds in the air of workplaces by flame atomic absorption spectrometry

Objective To evaluate the uncertainty of method for determining cadmium and its compounds in the air of workplaces by flame atomic absorption spectrometry. Methods According to the principle and method of the national occupational health standards, GBZ/T160.5-2004 and JJF 1059.1-2012, the components of uncertainty were calculated. Results The relative uncertainty of standard sampling volume was 0.008 4 and 0.004 8 for 75 L and 120 L, respectively. The uncertainty for the standard solution and preparation process, standard curve fitting, sample preparation process, and sample parallel determination was 0.006 6, 0.025 8, 0.030 0, and 0.001 5, respectively. The combined uncertainty was 0.041 0. The concentration of cadmium in the test sample was 0.067 mg/m3, and the expanded uncertainty for the measurement was 0.005 mg/m3 (k=2). The preparation process of sample solution, the fitting standard curve and the standard sampling volume were the main sources of the uncertainty of this method, and the other components had little influence on it. The uncertainty introduced by the sample digestion process in the preparation of sample solution made the greatest contribution to the combined uncertainty. Conclusion During experimental process, attention should be paid to reducing the loss of sample pretreatment and choosing high purity standard liquid and/or standard. Quality control should be improved in the process of sample preparation and calibration curve fitting. The uncertainty of results should be minimized to ensure the accuracy and reliability of the experimental data.