GENERAL PAPER

Accreditation and Quality Assurance

, Volume 6, Issue 1, pp 26-30

First online:

Uncertainty calculations in the certification of reference materials. 2. Homogeneity study

  • A.M.H. van der VeenAffiliated withNederlands Meetinstituut, Schoemakerstraat 97, 2600 AR Delft, The Netherlands e-mail: avdveen@nmi.nl Tel.: +31-15-2691 733 Fax: +31-15-261 2971
  • , T. P. LinsingerAffiliated withEuropean Commission, Joint Research Centre, Institute for Reference Materials and Measurements, Retieseweg, 2440 Geel, Belgium
  • , J. PauwelsAffiliated withEuropean Commission, Joint Research Centre, Institute for Reference Materials and Measurements, Retieseweg, 2440 Geel, Belgium

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Abstract

 Many reference materials undergo a batch certification, which implies that a small number of samples is taken from a batch, characterised, and these results are then assumed to be representative of all remaining samples. An important aspect in this design is the translation of the characterisation data to a single sample, as usually the laboratory will be using only one sample of the batch. This form of homogeneity is very important and can be influenced to a certain extent by well-designed sample preparation procedures. Another subsampling problem associated with many reference materials is that only a small test portion is drawn from the sample to carry out the measurement. Obviously, this test portion must be representative of the sample, otherwise the certified value is still not applicable. Both kinds of homogeneity tests are examined in the paper and evaluated using practical examples.

Keywords Reference materials Measurement uncertainty Analysis of variance Homogeneity study Minimum sample intake