GENERAL PAPER

Accreditation and Quality Assurance

, Volume 6, Issue 1, pp 20-25

Homogeneity and stability of reference materials

  • T. P. J. LinsingerAffiliated withEuropean Commission, Joint Research Centre, Institute for Reference Materials and Measurements (IRMM), 2440 Geel, Belgium e-mail: pauwels@irmm.jrc.be Tel.: +32–14–571 722 Fax: +32–14–590 406
  • , J. PauwelsAffiliated withEuropean Commission, Joint Research Centre, Institute for Reference Materials and Measurements (IRMM), 2440 Geel, Belgium e-mail: pauwels@irmm.jrc.be Tel.: +32–14–571 722 Fax: +32–14–590 406
  • , A.M.H. van der VeenAffiliated withNederlands Meetinstituut, Schoemakerstraat 97, 2600 AR Delft, The Netherlands
  • , H. SchimmelAffiliated withEuropean Commission, Joint Research Centre, Institute for Reference Materials and Measurements (IRMM), 2440 Geel, Belgium e-mail: pauwels@irmm.jrc.be Tel.: +32–14–571 722 Fax: +32–14–590 406
  • , A. LambertyAffiliated withEuropean Commission, Joint Research Centre, Institute for Reference Materials and Measurements (IRMM), 2440 Geel, Belgium e-mail: pauwels@irmm.jrc.be Tel.: +32–14–571 722 Fax: +32–14–590 406

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Abstract

 Homogeneity and stability are two crucial characteristics of any certified reference material (CRM). Utmost care must be taken during preparation to create materials as homogeneous and stable as possible. Degradation can generally be minimised by reducing the water activity of the material to a level between 0.15 and 0.35. However, careful preparation by itself is not enough. Positive demonstration of homogeneity and stability is required from the perspective of implementing uncertainty calculus according to the Guide to the Expression of Uncertainty in Measurement (GUM). In many cases, homogeneity and stability studies fail to give sufficient quantitative information on homogeneity and stability, mainly because of a lack of measurement repeatability and insufficient number of replicates. In this work, some solutions to these problems and their implications are presented.

Keywords Uncertainty Homogeneity Stability Certified reference material