Nordtest Handbook on Internal Quality Control

Bertil Magnusson, Life Science/Chemistry. Material and Surfaces, RISE Research Institutes of Sweden, Borås, Sweden
Håvard Hovind, Life Science/Chemistry. Material and Surfaces, RISE Research Institutes of Sweden, Borås, Sweden
Mikael Krysell, Life Science/Chemistry. Material and Surfaces, RISE Research Institutes of Sweden, Borås, Sweden
Ulla Lund, Life Science/Chemistry. Material and Surfaces, RISE Research Institutes of Sweden, Borås, Sweden
Irma Mäkinen, Life Science/Chemistry. Material and Surfaces, RISE Research Institutes of Sweden, Borås, Sweden

Internal quality control at the chemical analytical laboratory, involves a continuous, critical evaluation of the laboratory’s own analytical methods and working routines. The control encompasses the analytical process, starting with the sample entering the laboratory and ending with the analytical report. The most important tool in the quality control is the use of control charts. The basis is that the laboratory runs control samples together with the routine samples.
For internal quality control in the European countries the laboratories are extensively using the popular and very readable Trollbook available in 15 different languages. It is necessary that the quality control is limited to fulfilling the demands on the analytical results – a good balance between control work and analyses of samples is essential. The aim of this handbook is to describe a fit for purpose system for internal quality control at analytical laboratories. The approach is general but the examples are mainly from water analyses. The Trollbooks, TR 569 in most of the different languages are available at www.nordtest.info
In this lecture the important issues in the Trollbook will be pointed out; the issues are 1) the use of more reliable control limits and central line based on e.g. a one-year period, 2) introduction of target control limit 3) introduces the concept of method in control but out of statistical control 4) describes how to evaluate quality control data over longer time periods 5) proposes the use of quality control data giving you within laboratory reproducibility (intermediate precision) to be used in evaluating the uncertainty.

Figure 1. Example of an X control chart for the direct determination of zinc in water. All control values in the middle area (green. within the warning limits) show that the determination of zinc performs within given limits and the routine sample results are reported. Control values in the red area outside the action limits) show clearly that there is something wrong and no routine sample results are reported. A single value in the yellow area is accepted.