Intralaboratory quality control of chemical analysis with reference materials at disposal

In this problem-oriented article, regarding the author's experience, a review of the methods of intralaboratory quality control based on systematic analysis of reference samples (control materials) is given. The requirements imposed on reference samples are briefly considered. The principles of selection of an inspection plan and the requirements on the evaluation period of statistical characteristics are formulated. The techniques for graphically representing the results of intralaboratory control and the algorithms for detecting out-of-control analytical processes are considered. Control charts for average values and ranges or charts for cumulative sums and geometric (exponentially weighted) moving averages are recommended as the main or auxiliary graphical representation, respectively. Westgard rules and the simplest rules for ranges are recommended as the main algorithms for revealing out-of-control analytical processes. Multivariate statistical process control methods, which are recommended for use in the cases of a great number of simultaneously determined factors, are briefly discussed.