Homogeneity And Stability Of Materials Distributed Within The Wageningen Evaluating Programmes For Analytical Laboratories

Participation in laboratory evaluating programmes (Proficiency Testing schemes) is becoming increasingly important, especially for accredited laboratories. The Wageningen Agricultural University meets this need by organizing several world-wide international laboratory evaluating programmes on chemical analysis of soils (ISE), plants (IPE), manure, refuses (MARSEP) and sediments (SETOC). Since 1995, the existing programmes have been placed under an umbrella organization called WEPAL: Wageningen Evaluating Programmes for Analytical Laboratories. Because of the increasing importance of a good performance within the Proficiency Testing scheme, it is crucial that the organizer of the programmes can continue to guarantee a quality product. To achieve this, WEPAL reorganized and documented the complete system in order to get a formal accreditation (based on ISO/IEC Guide 43, part 1) as a qualified organizer of proficiency testing schemes. Much attention was paid to the topic of homogeneity and stability of the distributed materials. Based on a comparison of results obtained by i) participants of the schemes, ii) the Central Laboratory of the Sub-department Soil Science and Plant Nutrition and iii) a long-history of results, it may be concluded that the homogeneity and stability of the materials distributed through the ISE- and SETOC-schemes are sufficient for the goal of Proficiency Testing.