Three of the active substances, which had not been represented in any laboratory performance assessment to date, caused difficulties for the participating laboratories. This was reflected in a comparatively high number of quantification errors (10-24% of all participants).
One of them, the active substance spinetoram, an insecticidal natural substance consisting of two structurally similar components, spinetoram J (main component) and spinetoram L in the ratios 3:1 to 9:1.
The difficulty is that these two components have a very different LC-MS/MS response. This is unusual for an active substance of this type and complicates quantification. Therefore, a verification within the framework of the QS performance assessment is all the more important, since this active substance will be increasingly used in the future due to its origin from bacterial cultures - the actinomycetes, is the assessment of our laboratory expert Dr Günther Kempe.
The active substance metaflumizone was already tested in the 2020 laboratory performance assessment. At that time, the result showed a high number of quantification errors, which is why the active substance was tested again in the current test. Fortunately, an improvement in quantification was observed, although the active substance continued to cause problems for some laboratories.
Since it also has a different response of its structurally identical compounds due to its isomeric structure, it is particularly important for laboratories to gain as much experience as possible in its analysis.
The use of different standards could be another reason for the below-average results. Metaflumizone standards from 10 different origins/companies were used. Tests by the EURL (EU reference laboratory) showed that not all standards in circulation have a comparable ratio of the two isomers. In addition, the shelf life of the standards may play a role.