A matrix sensitive gas chromatography method for the analysis of pymetrozine in red pepper: Application to dissipation pattern and PHRL

A gas chromatography (GC) method for the analysis of pymetrozine was developed after utilizing matrix enhancement effect of pymetrozine to nitrogen phosphorus detector (NPD). Samples were extracted with acetonitrile and purified through primary secondary amine (PSA) and C18 dispersive sorbent. Matrix-matched calibration curve prepared after spiking standard pymetrozine across the studied range of concentrations (0.003-1.0 mg/L) into blank red pepper extract was excellent with a determination coefficients (R2) = 1. Recovery studies were carried out at three concentration levels (0.04, 0.4, and 2.0 mg/kg, n = 3) and the rates were ranged between 77.2% and 109.1%, with relative standard deviations ranged from 1.3% to 16.4%. The developed method was applied to field samples to characterize the dissipation pattern, half life, and pre-harvest residue limits (PHRL). The dissipation rates of the analyte were ascribed to first-order kinetics with half-life of 2.7 and 2.5 days for recommended and double the recommended doses. From the PHRL curve, we could predict that if the residue level of pymetrozine is below the 1.23 mg/kg at 10 days or 0.71 mg/kg at 7 days before harvest, then the residues will be below the maximum residue limits (MRL = 0.2 mg/kg) established by the Korea Food and Drug Administration (KFDA).