Experience of using the evaluations of the repeatability and reproducibility in compa­ ring test methods according to ISO 5725-6 "Accuracy (trueness and preci­ sion) of methods and measurement results. Part 6. Using precision values in practice"

   The trueness and precision indicators of two methods — complexometric titration and atomic absorption spectrometry (AAS) — were evaluated to select a method that would provide a higher accuracy of copper determination in a brass coating. In the titrimetric method of copper determination, the brass coating was dissolved in a mixture of ammonia and hydrogen peroxide and titrated with a solution of Trilon В in the presence of xylenol orange indicator, whereas for the atomic absorption method the coating was dissolved in nitric acid and the test solution was measured on an atomic absorption spectrometer. Two laboratories took part in the experiment. The results of measurements and the calculated precision indicators (repeat­ability and reproducibility) for both methods are presented. The intra-laboratory (intermediate precision) and general precision of the methods was compared using the Fisher test, whereas the overall average cop­ per content was compared with the certified value of a standard brass sample in accordance with ISO 5725-6 "Accuracy (trueness and precision) of methods and measurement results. Part 6. Using precision values in practice. " It is shown that the atomic absorption method is the most accurate among two consid­ered methods for determining the mass content of copper in a brass coating, as it has acceptable indicators of precision and trueness.

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