**2. Materials and Methods**

#### *2.1. Reagents and Materials*

Fluopyram (purity: 98%) was purchased from Sigma-Aldrich (St. Louis, MO, USA). The structure and physico-chemical properties of fluopyram are shown in Table 1 [10].


**Table 1.** Physico-chemical properties of fluopyram.

As a crop protection product, 40% suspension concentrate (SC) of fluopyram (Mercury, Bayer Crop Science Co., Ltd., Daejeon, Republic of Korea) was selected and purchased from a commercial agrochemical vendor. The analytical solvents, including acetonitrile and methanol, were purchased from J.T. Baker (Center Valley, PA, USA). High-performance liquid chromatography (HPLC) grade formic acid (purity: 99%) was purchased from Wako (Osaka, Japan) and ammonium formate (purity: ≥97%) was obtained from DAEJUNG (Siheung, Republic of Korea). Reagents used in the quick, easy, cheap, effective, rugged, and safe (QuEChERS) pretreatment method were purchased from Agilent Technology (Santa Clara, CA, USA). QuEChERS extract pouches (EN 15,662 method extraction kit; 4 g MgSO4, 1 g NaCl, 1 g sodium citrate dehydrate, and 0.5 g sodium hydrogencitrate

sesquihydrate) were used for partitioning, and dispersive solid phase extraction (d-SPE, 2 mL, 150 mg MgSO4 and 25 mg primary secondary amine (PSA)) was used for purification. A 100 mg/L stock solution was prepared by dissolving 10.20 mg of standard fluopyram (purity: 98%) in 100 mL of acetonitrile, and serially diluted using blank sample extracts to construct the matrix-matched working solutions at 1, 2, 5, 10, 20, 50, and 100 μg/L, which were used to correct for any matrix effects during the instrumental analysis. The stock and working solutions were stored at −20 ◦C in a freezer.
