The difficult-to-detect active substance chlorothalonil, which had already been investigated in three previous tests, also posed an analytical challenge in the current test. Both under-detections < 70% of the spiked value and over-detections above 120% were reported. The low findings are due to the known negative effect of the PSA additive (primary secondary amines) during sample purification. The excessive findings indicate matrix effects that were apparently not sufficiently taken into account during method validation for this matrix.
In contrast, the active substances penthiopyrad and permethrin, which were tested for the first time, were analyzed reliably and without problems by most laboratories. Also new in the test was the targeted individual determination of copper. A blind content of copper was already detected in the blank sample (organic starting material without spiked active substances). For this reason, the focus of the investigation was on the reliable identification of this element.
