Several proficiency tests were organized within the framework of a European project, called SWIFT-WFD, involved in implementing the Water Framework Directive (WFD). Among others, the parameters studied were polycyclic aromatic hydrocarbons (PAHs) and pesticides in organic standard solutions. The aim of this study was to evaluate the state of the art in Europe and possible sources of bias in calibration procedures. More than 30 laboratories across Europe took part in this study. These laboratories used their regular in-house analytical methods. We discuss the analytical results obtained. The averages of the results for all analytes partly agreed with the values of gravimetric sample preparation. Most of the participants in both exercises obtained satisfactory Z-scores. However significant outlier rates (in most cases around 20% of the data sets submitted) indicated that laboratories across Europe need to improve the quality of the analytical data that they deliver. We also raise some questions regarding the use of Z-scores to evaluate the laboratory performance. © 2007 Elsevier Ltd. All rights reserved.

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