Analysis of chlormequat / mepiquat in mushrooms and corresponding mushroom substrate (straw) method performance assessment

The competence in analyzing food products for Chlormequat/ Mepiquat residues was questioned, in particular, because of repeated Chlormequat findings in samples of organic mushrooms. Therefore, a method ringtest challenging the analytical competence was based on - an increased up-coming of Chlormequat/ Mepiquat residues in organic mushrooms, and - the questioned reliability of applied methods - in particular at concentration levels close to the BNN guideline value (10 μg/kg) which is applied for the evaluation of residue findings in organic food products. Assuming that the source of the analytes is the straw in the substrate on which the mushrooms are grown, the performed method ringtest also covers the analysis of Chlormequat / Mepiquat in substrate of straw. Additionally, one objective was to work out if there are any differences between the analysis of incurred residues in mushrooms or spiked pesticides (Chlormequat / Mepiquat) in mushrooms. Because of differences in analytical protocols and approaches, some concerns also came up related to the robustness and comparability of the analytical results, independent of applied techniques or protocols for different commodities. Therefore, an appropriate method ring test including also a statistical evaluation of the analytical results was designed, organized and performed, in order to provide an integrated approach to assess the validity, comparability and robustness of the applied different methods. The statistical evaluation and critical review of the reported results indicate that the analysis of Chlormequat / Mepiquat is generally robust but also challenging. Even though the applied methods share a basic instrumental element (LC-MS/MS module), the reported results show considerable deviations - in particular, related to the determination of Mepiquat.