2.1.3. Reagents

The extraction salt kit (4 g MgSO4, 1 g NaCl, 0.5 g disodium citrate sesquihydrate, and 1 g trisodium citrate dehydrate) and dispersive solid phase extraction (dSPE) kit (25 mg primary secondary amine and 150 mg MgSO4) were purchased from Chromatific (Heidenrod, Germany). Acetonitrile, methanol (Merck, Darmstadt, Germany), formic acid (purity: 99%) (Wako, Osaka, Japan), and ammonium acetate (purity: 99%) (Sigma-Aldrich, St. Louis, MO, USA) were of liquid chromatography grade. Vegetable detergent (CaO, 100%), alkaline water (water 99.99%, calcium hydroxide 0.005%, magnesium hydroxide 0.005%) (pH 9.3), vinegar, and sodium bicarbonate were obtained from Ecobiotec Co., Ltd. (Gyeonggi-do, Hwaseong-si, South Korea), Auskorea Co., Ltd. (Gyeonggi-do, Seongnam-si, South Korea), Daesang Corp. (Seoul, South Korea), and LG Household & Health Care Ltd. (Seoul, South Korea), respectively.

#### *2.2. Sample Preparation and Washing Treatments*

The following five leafy vegetables with the highest rate of pesticide detection were selected: lettuce, perilla leaves, spinach, crown daisy, and ssamchoo [19,20]. The samples were randomly purchased from the Gakhwa Agricultural Products Wholesale Market (Gwangju, South Korea) in 2021. Samples of the five leafy vegetables were pre-analyzed and determined to be free of previous residues prior to the experiment and stored at 4 ◦C prior to analysis. The pesticides used to prepare the contaminated samples were administered according to the doses recommended by the manufacturer. The recommended doses were 20 mL/20 L for diniconazole and indoxacarb and 10 mL/20 L for chlorfenapyr, azoxystrobin, imidacloprid, chlorantraniliprole, fludioxonil, and lufenuron. The recommended amounts of thiamethoxam and pyraclostrobin were 10 g/20 L and 6.7 g/20 L, respectively. The concentration of the 10 pesticides in the mixed solution ranged from 13.5–108.5 mg/L. Leafy vegetables were soaked in 20 L of mixed pesticide and treated for 10 s to ensure even application of the pesticide. Contaminated leafy vegetables were air-dried in a fume hood for 15 h at room temperature. Subsequently, 100 g of the contaminated leafy vegetables was randomly collected to detect the initial residual amount. The contaminated samples were washed using nine methods. The treatment time was set to 5 min, which is the mid-point of the treatment time used in previous studies, and was unified, except for blanching (30 s), to compare the washing effect [13]. Each process was repeated five times.

(a) Running tap water: Samples (100 g) were rinsed under running tap water for 5 min. The running rate of the tap water was controlled at 170 mL/s.

