*3.2. Validation of the Analytical Method*

The method validation was performed according to the European SANTE/12682/2019 guidelines [15]. During the analysis, no peak was detected at the retention time of fluopyram, indicating that there were no interferences affecting its detection. An analyte signal during ionization is enhanced or suppressed due to matrix components co-eluted with the analyte of interest, which is known as the matrix effect. Therefore, a matrix-matched calibration is necessary to compensate for the matrix effect during MS analysis. The MLOQ of fluopyram was calculated to be 0.01 mg/kg for soil and scallions.

**Figure 1.** Growth characteristics of scallions during the cultivation period.

The linearity of the matrix-matched calibration curves was good, with R2 > 0.9996 in soil and scallions, which satisfied the criteria of >0.98. As shown in Table 3, the average recovery efficiencies from soil and scallions were 71.3–96.3% with RSDs ranging from 0.4 to 2.2%, which was satisfactory with a recovery of 70–120% and reasonable RSDs ≤ 20%. These results demonstrated that the analytical method developed in this study had satisfactory precision and accuracy for quantifying fluopyram residues in soil and scallions.


**Table 3.** Recovery efficiencies for fluopyram in soil and scallions.

<sup>1</sup> Mean ± standard deviation of triplicate samples. <sup>2</sup> Matrix-dependent limits of quantitation.
