氯化钙法分析土壤中重金属可提取态的精密度探讨

精密度是实验室进行质量控制的主要技术指标。目前,氯化钙法分析土壤中重金属可提取态的精密度控制指标尚未建立。采集制备5个水平土壤样品,分层随机抽取15瓶样品进行均匀性检验,分析结果采用单因素方差分析法评价,表明5批土壤样品均匀性良好。组织8家实验室开展了氯化钙法分析土壤中Cd、Cu、Ni、Zn等4种重金属可提取态的精密度试验,按照国标方法GB/T 6379.2—2004《测量方法与结果的准确度 第2部分:确定标准测量方法重复性与再现性的基本方法》进行统计分析,采用科克伦(Cochran)准则和格拉布斯(Grubbs)准则检验单元间试验数据精密度和平均值的一致性,评价了方法的重复性限(r)和再现性限(R)等精密度指标。其中Cd、Cu、Ni、Zn在0.143~7.69、0.40~24.7、0.32~2.55、3.09~181 mg/kg含量范围内,重复性限分别在0.013~0.32、0.04~1.4、0.02~0.11、0.18~7.8 mg/kg之间;再现性限分别在0.032~0.64、0.10~5.8、0.08~0.61、0.31~20 mg/kg之间。通过将重复性限和再现性限与其含量进行迭代回归统计分析,确定了分析方法重复性限和再现性限与含量的函数关系式,并进行了初步实验验证,为氯化钙法分析土壤中重金属可提取态的质量控制提供了科学依据,也为该标准方法的制订提供了数据支持。

Discussion on the precision for determination of extractable heavy metals in soil by calcium chloride method

The precision was the main technical index for quality control in laboratory test. Until now, the precision control indexes for the determination of extractable heavy metals in soil by calcium chloride method have not been established. The soil samples with five levels were prepared. The homogeneity test was performed from 15 bottles selected by stratified random sampling. The analysis results were evaluated by single-factor analysis of variance (ANOVA) method, and it was indicated that the homogeneity of five batches of soil samples was good. Eight laboratories were organized to participate in precision tests in determination of four extractable heavy metals (Cd, Cu, Ni and Zn) in soil by calcium chloride method. Statistical analysis was carried out according to the national standard method of GB/T 6379.2-2004 for Accuracy (trueness and precision) of measurement methods and results-Part 2: Basic method for the determination of repeatability and reproducibility of a standard measurement method. Cochran criterion and Grubbs criterion were used to verify the consistency of precision and average of test data between units. The precision indexes such as reproducibility limit (r) and reproducibility limit (R) were evaluated. When the content of Cd, Cu, Ni and Zn was in range of 0.143-7.69, 0.40-24.7, 0.32-2.55 and 3.09-181 mg/kg, the repeatability limit was 0.013-0.32, 0.04-1.4, 0.02-0.11 and 0.18-7.8 mg/kg, and the reproducibility limit was 0.032-0.64, 0.10-5.8, 0.08-0.61 and 0.31-20 mg/kg, respectively. The repeatability limit, reproducibility limit and the content were analyzed by iterative regression statistics to obtain the function relationship between repeatability limit, reproducibility limit of analytical method and the content, and the preliminary experimental verification was conducted. The study provided scientific basis for laboratory quality control in analysis of extractable heavy metals in soil, and also provided data supports for the development of standard method.