Wageningen evaluating programmes for analytical laboratories (Wepal), organization and purpose

Quality control of analytical procedures for soils, plants, sediments, manure, compost, and sludges is of utmost importance to produce reliable and reproducible analytical data. For this purpose first, second, and third line quality control measures are taken in analytical laboratories. For first line control certified reference materials (CRM's) are preferred. However, the number and matrix variation in CRM's for environmental analytical research is still very limited. For second line control internal reference samples are often used, but again here the values for many element and parameter concentrations are questionable since almost no check versus CRM's is possible. For third line control participation in laboratory-evaluating exchange programmes (LEEP's) is recommended. The number of LEEP's is fortunately increasing nowadays. One of the reasons for this increase is the fact that accredited laboratories are recommended, and in some countries, obliged to participate in LEEP's - if they exist - for their analytical programs. In this article the Wageningen Evaluating Programmes for Analytical Laboratories (WEPAL) for plants, soils, sediments, manures, composts, and sludges are described and examples of results achieved and further use of tested bulk samples are given.