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QS laboratory performance assessment - Results in detail 1/2023

Some laboratories in the recognition procedure were unable to detect the metabolite spirotetramat-enol. This was largely due to the fact that they did not test all metabolites relevant for the residue definition of the sum active substance spirotetramat in their spectrum.

The herbicidal active substance pendimethalin was already tested in 2019/1. At that time, there were an increasing number of quantification errors for the active substance. 18% of all laboratories reported levels that were mostly too low. In the current test, some laboratories still showed weaknesses in quantification. However, the percentage of quantification errors decreased. Pendimethalin is not difficult to analyze but great care must be taken when handling this substance.

Since it has a relatively high volatility, errors can occur, especially when preparing or handling the calibration solutions.

In the evaluation of the submitted results in the test report, emphasis was placed on the consideration of the conversion factor for spirotetramat-enol for the calculation of the legal maximum residue limit. For active substances with a sum residue definition, the molar weight for each component (metabolite) must be considered in relation to the molar weight of the parent substance (parent substance divided by metabolite). The factor calculated from this must be multiplied by the measured value of the metabolite and summed with the concentration of the parent substance to obtain a correct summed value. Some laboratories have not taken this factor into account when reporting the summed value. Correction is required here.

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