增量取样量接近分析试样量时的取样——理论修正与结果  

Sampling when the Increment Size Approaches the Analytical Aliquot Size——Theoretical Modifications and Consequences

作　　者：MINKKINEN Pentti MINKKINEN Pentti(Lappeenranta University of Technology,Lappeenranta 53851,Finland)

机构地区：[1]拉彭兰塔理工大学,芬兰拉彭兰塔53851

出　　处：《中国无机分析化学》2020年第4期1-8,共8页Chinese Journal of Inorganic Analytical Chemistry

摘　　要：化学分析取样几乎总是一个多步骤过程,所有的步骤都会导致分析结果的总体不确定性。样品采取之后,不论后续采样过程如何精细,前期采样阶段的误差都无法在后续采样过程中更正。第一次取样是最重要的,通常其方差远远超过实验室测量的方差。但这不意味着在最终实验室分析试样制备阶段可以忽略采样理论的原理。现代分析仪器旨在处理小样本(从毫克到几克)。在这种情况下,如果样品是包含少量分析物的混合颗粒,则物料的不均匀性可能会很大以至于破坏整个分析过程。不均匀性计算和样品制备过程中基本采样误差方差的估计对于开发适用的分析程序至关重要。在样本制备的最后步骤中,新的增量本是父增量本的重要组成部分,在估算样本方差时必须考虑到这种影响。TOS提供了用于处理这些情况的工具。通过两个案例阐明了不均匀性计算的应用。在第一个例子中,评估了鸡饲料中低含量添加剂的成分不均匀性,在第二个例子中,对样品制备进行了优化,以校正用于分析硅灰石精矿中矿物杂质含量的红外仪器。在处理颗粒混合物和评估混样效率时,不均匀性评估也很重要。Sampling for chemical analysis is nearly always a multi-stage process where all stages contribute to the total uncertainty of the results reported.A sample,when extracted from the target,forgets its past,consequently,mistakes made in earlier stages of this process cannot be corrected at later stages,no matter how carefully and precisely they are executed.Primary sampling is the most important,and generally,its variance by far exceeds the variance of the laboratory measurement.That does not mean that,at the later stages when laboratory and analytical aliquots(or test portions)are prepared,the principles of the theory of sampling(TOS)can be neglected.Modern analytical instruments are designed to handle small samples(from milligrams to a few grams).In this case,if the sample is a mixture containing a low fraction of analyte containing particles,the constitution heterogeneity of the material may be so large that it ruins the whole analysis.Heterogeneity calculations and evaluation of the fundamental sampling error variances of the sample preparation steps are essential in developing fit-for-purpose analytical procedures.At the final steps of the sample preparation the new subsample is a significant part of parentsub-sample and account of that effect has to be taken in estimating the sampling variances.TOS offers tools for handling also these situations.Application of heterogeneity calculations are elucidated with two illustrative examples.In the first example the constitution heterogeneity is estimated for low concentration additives in chicken feed and in the second example the sample preparation is optimised for calibrating an IR instrument for estimating mineral impurities in a wollastonite concentrate.Heterogeneity assessments are important also when particle mixtures are processed and the efficiency of mixing is estimated.

关 键 词：采样 误差方差 理论修正 

分 类 号：O65[理学—分析化学]