*4.2. Instruments and Apparatus*

A nitrogen evaporator (N-Evap-111; Organomation Associates, Berlin, MA, USA), centrifuge (Allegra X-22R; Beckman Coulter, Fullerton, CA, USA), nitrogen generator (Model 05B, System Instruments Co., Tokyo, Japan), and vortex mixer (type 37,600 mixer, Barnstead Thermolyne, Dubuque, IA, USA) were employed in this study for sample preparation. For LC-amenable sulfonamides, LC-MS/MS consisted of a mass spectrometer (ABI 4000 QTRAP, Applied Biosystems, Foster City, CA, USA) in electrospray ionization (ESI) mode and an UltiMate 3000 HPLC system (Thermo Fisher Scientific, Waltham, MA, USA). HPLC separation was executed using an Acquity UPLC® HSS T3 C18 column (2.1 mm internal diameter × 1.8 μm film thickness ×100 mm; Waters, Milford, MA, USA) with chromatographic conditions at 40 ◦C. To determine the levels of residues of LC-amenable organophosphorus insecticides, the liquid chromatography–tandem mass spectrometry (LC-MS/MS) apparatus comprised an UltiMate 3000 HPLC system and a mass spectrometer (TSQ quantiva triple quadrupole; Thermo Fisher Scientific, Austin, TX USA). In addition, LC-amenable organophosphorus insecticides were separated using a CORTECS UPLC C18 column (2.1 mm internal diameter × 1.6 μm film thickness ×100 mm; Waters, Milford, MA, USA). To analyze gas chromatography (GC)-amenable organophosphorus insecticides, GC-tandem mass spectrometry (GC-MS/MS) was executed on a GC system (Thermo Scientific Trace 1310; Thermo Fisher Scientific, Austin, TX USA) as well as a mass spectrometer (TSQ 8000 triple quadrupole, Thermo Fisher Scientific) that was coupled with Rxi®-5Sil MS fused silica capillary column (0.25 mm internal diameter × 0.25 μm film thickness × 30 m; Restek, Bellefonte, PA, USA).

#### *4.3. Standard Solution Preparation*

To prepare stock solutions of individual sulfonamides and organophosphorus insecticide standards in this study, a portion of each analyte (100 mg) was accurately weighed and dissolved in volumetric flasks containing 100 mL of acetone, ACN, or MeOH, according to analyte solubility. For the preparation of working standard mixtures, all stock solution types were combined and subsequently diluted to 1 mg/L. For storage, all solutions were maintained at −20 ◦C; however, before each use, they were brought to room temperature. The prepared working standard solutions were applied to derive a series of calibration standards through serial dilution in the 1–500 ng/mL range.
