2.4.2. Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS) Analysis

The pesticides (azoxystrobin, chlorantraniliprole, fludioxonil, imidacloprid, lufenuron, pyraclostrobin, and thiamethoxam) were analyzed using a nanospace NASCA (OSAKA SODA, Tokyo, Japan) liquid chromatograph with a QTRAP 4500 detector (AB Sciex, Framingham, MA, USA). The target pesticides were separated on a CAPCELL CORE C18 column (2.1 mm I.D. × 150 mm, 2.7 μm) (OSAKA SODA, Tokyo, Japan) maintained at 40 ◦C. The mobile phase was 5 mM ammonium acetate in water with 0.1% formic acid (phase A) and 5 mM ammonium acetate in methanol with 0.1% formic acid (phase B). The following gradient was employed: 95:5 (A:B) (0–1 min), 40:60 (1–3 min), 0:100 (3–13 min), and held for 18 min, and finally maintained at 95:5 (18.1–25 min). The flow rate was 200 μL/min. Two microliters of the final extracted sample solution were injected into the system. The analysis time was 26.05 min. Quantification and identification of the target compounds were carried out in multiple reaction monitoring mode. Electrospray ionization was conducted in positive ion mode (ESI+) and negative ion mode (ESI−) at capillary voltages of 5500 and −4500 V, respectively, and evaporation of solvents with synthetic air at 450 ◦C. Table 2 summarizes the LC-MS/MS parameters.
