A Modified QuEChERS Combined With HPLC-MS/MS for the Determination of Emamectin Benzoate, Spinetoram, and Their Major Metabolites in Eggplant Field Samples

To control thrips in eggplant cultivation, a new pesticide formulation (9% emamectin benzoate·spinetoram microemulsion) is under registration in China. However, the residues of emamectin benzoate (EMB), spinetoram, and prime metabolites of spinetoram in eggplant remained unclear. In this study, field trials were performed in accordance with good agricultural practice across eight provinces of China. The pesticide formulation was sprayed once at 13.5 g a.i./ha, and the recommended pre-harvest interval was 7 days. For the simultaneous determination of EMB, spinetoram, and its metabolites in eggplant, a modified quick, easy, cheap, effective, rugged, and safe method combined with high-performance liquid chromatography tandem mass spectrometry was developed and validated. The combination of 25 mg of primary-secondary amine, 25 mg of Nano-ZrO 2 , and 5 mg of multi-walled carbon nanotubes was applied to purify the eggplant extracts. Method validation demonstrated excellent linearity ( r ≥ 0.9991), acceptable accuracy with recoveries of 82.7%–102.6%, precision (relative standard deviations ≤7.7%), sensitivity (limits of detection, 6.59 × 10 −5 –3.06 × 10 −3 ng; limits of quantification, 0.0025–0.01 mg/kg), and matrix effects (≤25.2%). When harvested after the recommended 7-day interval, the residues of EMB (<0.01 mg/kg) and spinetoram (≤0.025 mg/kg) in eggplant were lower than the maximum residue limits in China. The residues of metabolites N- formyl-XDE-175-J and N- demethyl-XDE-175-J in eggplant were lower than the limits of quantification (0.01 mg/kg). This study offers recommendations for the effective use of this pesticide formulation on eggplant.