## 3 Results and Discussion
### Sample Preparation Optimization  
In order to determine the optimal extraction conditions for pesticides in water, three extraction protocols, namely HLB1, HLB2, HLB3, (as shown in Table S2) were evaluated in triplicate (\(n=3\)). In all cases, Onsis HLB extraction cartridges (200 mg, 6 mL) were utilized due to their superior efficacy in extracting polar pesticides [31; 32; 33], given that they are specifically designed with a hydrophilic-lipophilic balance to ensure optimal results. The efficiency of the three procedures was examined under various extraction conditions. In the HLB1 and HLB3 protocols, the pH of the sample was not modified prior to extraction. However, in the HLB2, the sample was acidified to achieve a final pH of 2.5-3. The HLB1 and HLB3 protocols involved activation and equilibration of the adsorbent by sequentially adding 5 mL of methanol and 5 mL of LC-MS grade water. In contrast, the HLB2 procedure utilized acidified LC-MS water with a pH range of 2-2.5 for this stage. In all three situations, the volume of the sample was 250 mL, while the flow rate remained constant at approximately 1-2 mL min\({}^{-1}\). Regarding the washing of the cartridges once the full sample volume was loaded and prior to elution, 5 mL of LC-MS grade water was used in all three tests. During the elution process, 2 \(\times\) 5 mL of methanol (MeOH) was used for HLB1 and HLB2. In HLB3, a mixture of solvents was utilized: 3 mL of dichloromethane, 3 mL of hexane, and 3 mL of acetone, in that specific order, collected in the same tube. The eluate was dried using a moderate stream of nitrogen and then dissolved again in 500 mL of the initial mobile phase (90% H\({}_{2}\)O/MeOH and 0.1% formic acid (\(v/v\))). Figure 1 and Table S3 depict the recovery rates of pesticides obtained by the three tested extraction protocols. For most of the selected pesticides, the recoveries were largely within acceptable ranges for all the three protocols. Namely, yielded recoveries ranged from 61% to 96% for \"HLB1\". However, for \"HLB2\", the recoveries ranged between 37% and 87%; some of them were calculated below the acceptable limits. Despite the varying p\(K_{\alpha}\) values of the selected pesticides, typical acidic pesticides were not included in the target list; hence, acidified extraction conditions did not favor significantly the obtained recoveries. Recoveries obtained by \"HLB3\", which employed a combination of elution solvents, varied between 49% and 95%. HLB2\" and \"HLB3\" methods resulted in a significant proportion of compounds with recoveries that were deemed unacceptable, rendering them inappropriate for a multi-residual analysis. linearity. Table 1 provides information on the detection and quantification limits, the linear range, and the correlation coefficient (r\({}^{2}\)) for the compounds. Method accuracy was investigated by means of trueness (recovery) and precision [34]. The selected spiking concentration levels for the compounds were 10 ng L\({}^{-1}\), 50 ng L\({}^{-1}\), and 200 ng L\({}^{-1}\). For each concentration level, five samples (\(n=5\)) were spiked and analyzed within the same day to determine method repeatability expressed as RSDr, while intra-laboratory reproducibility (RSD\({}_{\mathrm{wR}}\)) was assessed by three successive days of analysis (\(n=3\times 5=15\)). The mean recovery values (\(n=5\)) for the pesticides in river waters varied from 59% (chlorantraniliprole) to 104% (fluazifop-p-butyl) at the low spiking level, from 61% (thiacloprid, boscalid) to 96% (imazalil) at the medium level, and from 68% (dimethoate) to 93% (fluazifop-p-butyl) at the high level. In the case of sea water, the recoveries were marginally elevated, primarily as a result of greater ionic strength and matrix effect [35]. The recoveries ranged from 62% (chlorantraniliprole) to 111% (fluazifop-p-butyl) at the low level, from 60% (thiacloprid) to 95.4% (imazalil) at the medium level, and from 68% (dimethoate) to 97.2% (fluazifop-p-butyl) at the highest level.