Intralaboratory quality control of chemical analysis with reference materials at disposal

In this problem-oriented article, regarding the author's experience, a revi ew of the methods of intralaboratory quality control based on systematic an alysis of reference samples (control materials) is given. The requirements imposed on reference samples are briefly considered. The principles of sele ction of an inspection plan and the requirements on the evaluation period o f statistical characteristics are formulated. The techniques for graphicall y representing the results of intralaboratory control and the algorithms fo r detecting out-of-control analytical processes are considered. Control cha rts for average values and ranges or charts for cumulative sums and geometr ic (exponentially weighted) moving averages are recommended as the main or auxiliary graphical representation, respectively. Westgard rules and the si mplest rules for ranges are recommended as the main algorithms for revealin g out-of-control analytical processes. Multivariate statistical process con trol methods, which are recommended for use in the cases of a great number of simultaneously determined factors, are briefly discussed.