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The standards for thiamethoxam (99.6%), clothianidin (99.7%), and thiamethoxam-urea (99.3%) were provided by Dr. Ehrenstorfer GmbH (Augsburg, Germany). The commercial formulation of thiamethoxam water-dispersible granules (25% WDG) was purchased from Syngenta Crop Protection Co., Ltd. (Basel, Switzerland). LC-MS (liquid chromatography-mass spectrometry)-grade methanol and acetonitrile were supplied by Merck (Darmstadt, Germany). LC-MS-grade ammonium acetate was obtained from ThermoFisher Scientific (Waltham, MA, USA). The QuEChERS extraction salt packets (EN method, European Norm method) and d-SPE (dispersive solid-phase extraction) sorbent purification packets were purchased from Agilent (Agilent Technologies, Lake Forest, CA, USA).
High-level standard solutions (1000 mg L⁻¹) of TMX, CLO, and TMX-urea were prepared independently in methanol. The mixed standard solutions at the required concentration were diluted with acetonitrile. All solutions were stored at −20 °C in the dark before use to avoid degradation. The multiple-level working solutions of TMX, CLO, and TMX-urea that were used to create a calibration curve were prepared with acetonitrile by gradually diluting the mixed standard solutions.

Bifenthrin (purity; 99.0%), butachlor (95.9%) standards, and ammonium formate (10 M) were purchased from Sigma-Aldrich (St. Louis, MO, USA). Commercial pesticide products were Talstar [Bifenthrin 1 EC (NongHyup Chemical Co., Ltd., Seongnam, Korea)] and Macet [butachlor 5 GR (FarmHannong Co., Ltd., Seoul, Korea)]. HPLC grade acetonitrile (MeCN) and ethyl acetate (EA) were obtained from Samchun Chemical (Seoul, Korea) and from Duksan Pure Chemical (Seoul, Korea), respectively. LC–MS grade methanol (MeOH) and formic acid (>99%) were purchased from Thermo Fisher Scientific (Waltham, MA, USA). LC–MS grade water was obtained from Merck (Darmstadt, Germany). Acetic acid (99.5%) was purchased from Junsei Chemical Co., Ltd. (Tokyo, Japan). QuEChERS extraction original kit (4 g of magnesium sulfate; MgSO₄ and 1g of sodium chloride; NaCl), EN 15662 kit (4 g of MgSO₄, 1 g of NaCl, 1 g of sodium citrate; Na₃Citr·2H₂O, and 0.5 g of sodium hydrogen citrate sesquihydrate; Na₂HCitr·1.5H₂O), d-SPE, PSA (25 mg of PSA and 150 mg of MgSO₄), and GCB (25 mg of PSA, 7.5 mg of bulk carbonate, and 150 mg of MgSO₄) were obtained from Agilent Technologies (Santa Clara, CA, USA). Oasis PRiME HLB cartridge plus light (100 mg) was purchased from Waters Corporation (Milford, MA, USA).

Pesticide standards, namely, chlorpyrifos–methyl, deltamethrin, fenoxanil, fludioxonil and thiobencarb were purchased from Dr. Ehrenstofer (LGC, Ltd., Teddington, UK). All analyte standards had purity of ≥98%. MeCN, n-hexane, DW and concentrated CH₂O₂ were of analytical reagent grade and purchased from Thermo Fisher Scientific (Waltham, MA, USA). Individual stock solutions of each standard were diluted in MeCN at a concentration of 1000 µg/mL. The QuEChERS packet containing 4 g MgSO₄, 1 g NaCl, 1 g sodium citrate and 0.5 g disodium citrate sesquihydrate, EMR-lipid^TM, d-SPE containing 150 mg of MgSO₄, 25 mg of PSA and 25 mg of C18 (EN15662) and 150 mg of MgSO₄, 50 mg of PSA and 50 mg of C18 (AOAC) and homogenizer were obtained from Agilent Technologies (Santa Clara, CA, USA).