## 2 Results and Discussion
### Optimization of UPLC-HRMS Conditions  
The chromatographic conditions were carefully optimized to obtain the desired separation and retention on a column for the target analytes. Firstly, several experiments were carried out using different mobile phases, consisting of methanol or acetonitrile as the organic phase and water phase, respectively, with different proportions of formic acid in the range of 0.05% to 0.5%, as well as ammonium acetate and ammonium formic ranging from 1 mmol/L to 10 mmol/L. The results showed that methanol was more suitable since it was less polar and gave rather better chromatographic separation results than acetonitrile. Secondly, the addition of formic acid-ammonium acetate achieved much better results than that of formic acid-ammonium formic, since the ionization efficiency could be obviously improved. Finally, the optimal mobile phases were achieved using methanol as an organic solvent and water with 0.1% formic acid (\(v/v\))-ammonium acetate (5 mmol/L). Furthermore, we selected several UPLC columns (C\({}_{8}\), C\({}_{18}\), Waters High Strength Silica (HSS) T\({}_{3}\)) to optimize the chromatographic retention of the nine target fungicides. Carbendazim, which was the most polar among the nine fungicides, was selected as the representative fungicide. As shown in Figure 2 carbendazim showed poor retention on the C\({}_{18}\) column (\(t\) = 0.56 min, Figure 2a) because the structure of carbendazim was strongly polar. Better retention was obtained on the C\({}_{8}\) column at 1.07 min (Figure 2b). However, satisfactory retention could be observed when using the Waters HSS T\({}_{3}\) column (\(t\) = 1.97 min, Figure 2c), which can analyze polar structures. Therefore, Waters HSS T\({}_{3}\) was selected as the separation column for the analysis of the nine fungicides. The typical selected ion monitoring (SIM) chromatogram of the nine target fungicides was shown in Figure 3, and it could be observed that their peaks were symmetrical and well separated. Figure 3: _Cont_. Figure 2: Selected ion monitor (SIM) chromatograms of carbendazim using different columns: (**a**) C\({}_{18}\) column; (**b**) C\({}_{8}\) column; and (**c**) Waters High Strength Silica (HSS) T3 column. The optimization of the HRMS conditions for the qualitative and quantitative analysis of the nine fungicides and their IS was achieved by determining the analytes using flow injection analysis. The sensitivity of the nine fungicides was verified by recording the chromatogram peak areas in a full mass scan under the positive ionization mode. The optimal UPLC-HRMS conditions for the nine fungicides were listed in Table 1. In Full MS/dd-MS\({}^{2}\) mode, a Full MS scan was firstly carried out, and then a dd-MS\({}^{2}\) scan was triggered, wherein the ions designated in the inclusion list or ions strong enough under the Full MS mode were chosen by quadrupole. Further, 1.0 Da was selected as an isolation width for the quadrupole. Furthermore, \(N\) corresponds to the loop count (\(N\) = multiplex \(\times\) loop count, multiplex was set as five). Hence, the dd-MS\({}^{2}\) spectra of the analytes only in Top 5 were carried out in the inclusion list with a mass deviation of less than 5 ppm at a certain retention time and above the set threshold. As shown in Table 1, the mass deviations of the nine fungicides were all less than 3.0 ppm.