The objectives of the CORESTA Agrochemical Analysis Sub-Group are to perform regular proficiency testing of multi-residue methods for the analysis of Crop Protection Agents in tobacco, to undertake joint experiments to resolve identified issues, and to publish and review a series of Technical Notes and Guidelines for method development and improvement.

Annual studies include more than 20 participants from regulatory, manufacturers, and independent commercial and research laboratories.

This paper reviews the results from nine Proficiency Tests conducted since 2005 using the FAPAS testing scheme. The results indicate that continuous ring trials improve the quality of participating laboratories significantly over time. Big differences in improvement were found between regular and occasional participants. The paper also discusses evaluation issues which arise when participating laboratories do not provide data for the full set of test articles. However, when calculating the weighted average of squared z-scores for all studies, a decrease from 4.5 to 2.5 is observed indicating significant progress in quality through joint experiments, scientific dialogue and exchange of available knowledge.