## 3 Results and Discussion
### Method Evaluation
The higher retention time difference between compounds under the confirmatory analysis was caused by the steep gradient elution and by the different MRM dwell time settings. In this case, the appropriate identification was supported by the standard addition quantification. As a matter of fact, the SANTE guideline allows for the quantification through neat solvent calibration [19]. However, if calibrants in neat solvent had been used, the retention time difference between the interfering matrix compound and propham would not have been observed. Therefore, the use of standard addition is necessary if the corresponding isotopically labelled analogue as ISTD is not included in the method. Ruling Out the False Identification of Quinoclimine in Fennel (Foeniculum vulgare) with the Help of Standard Addition and the Third MRM Transition  
Positive identification of quinoclimine in a fennel sample was recorded during the screening analysis. The retention time of the supposed analyte, quinoclimine, in the neat solvent, and in the fennel sample, was 6.55 min and 6.54 min, respectively. Both ion transitions (\(m/z\) 208 \(>\) 77 and \(m/z\) 208 \(>\) 105) showed distinct peaks for quinoclimine and the IR values in the neat solvent (84.7%) and in the sample (82.6%) were close to each other (Figure 5a). Figure 4: (**a**) Screening analysis of propham in an elderberry sample. Relevant signals in the expected retention time (7.80 min) with tolerable IR difference appeared on the ion transitions of \(m/z\) 180 \(>\) 138 and \(m/z\) 180 \(>\) 120. (**b**) Confirmatory analysis of propham in elderberry sample. The retention time difference between the target compound (indicated by the arrow at 4.25 min) and the interfering matrix peak (4.21 min) can be clearly observed with the help of the standard addition process (below). Figure 5: \(Cont.\)  
The close retention time between the interfering matrix peak and the target compound remained the same under the confirmatory analysis (at 4.71 min). Finally, the interference and the analyte could only be distinguished by monitoring a third ion transition (\(m/z\) 208 \(>\) 172) for quinoclamine to achieve adequate selectivity. Indeed, only the target compound gave signal on the third ion trace (Figure 5b), hence the application of more than two ion transitions per compound was highly required. Again, involving a third MRM transition, similarly to what [PERSON] et al. presented in their study [22], was necessary to make decision on the target compound. Ruling Out the False Identification of Teufenpyrad in Dried Ginger (Zingiber officinal) with the Help of Standard Addition and More MRM Transitions  
Teufenpyrad elutes at 11.93 min during the screening analysis (\(m/z\) 334 \(>\) 145 and \(m/z\) 334 \(>\) 117, IR = 76.2%). During the screening of a dried ginger sample (Figure 6a) signals on both ion traces of tebufenpyrad appeared at 11.87 min (IR = 69.2%). Both the retention times and the IRs were within the tolerance range (\(\Delta\) 0.1 min and \(\pm\)30%). The standard addition to the sample during the confirmation analysis clearly showed that the sample did not contain tebufenpyrad over the limit of detection (Figure 6b). Retention time difference between the target compound and the matrix peak was observed. This was further confirmed by monitoring twelve ion transitions for tebufenpyrad from which only four ion traces (\(m/z\) 334 \(>\) 145, \(m/z\) 334 \(>\) 117, \(m/z\) 334 \(>\) 114, \(m/z\) 334 \(>\) 91) could be detected for the interfering peak (Figure 6c). Again, the standard addition calibration could indicate that the identified compound is not the targeted, which was further confirmed by setting several ion transitions. This means that the retention time tolerance of 0.1 min can be deceptive in some particular cases. Figure 5: **(a)** Screening analysis of a fennel sample. The ion transitions of quinoclamine in a neat solvent calibrant (100 ng/mL, below) and in the sample (above). **(b)** Confirmatory analysis of the fennel sample for quinoclamine with standard addition.