Single‐step modified QuEChERS for determination of chlorothalonil in shallot (Allium ascalonicum) using GC‐μECD and confirmation via mass spectrometry

A single extraction method was developed for chlorothalonil in shallot using gas chromatography with an electron capture detector (GC-mECD). Samples were extracted with single-step modified quick, easy, cheap, effective, rugged, and safe (QuEChERS) method using ethyl acetate as an extraction solvent. Significant matrix effects were observed, and the calibration curve was constructed from the matrix. The linearity of the analytical response across the studied range of con- centrations (0.01-1.00mg/L) was excellent, obtaining a correlation coefficient (r 2 ) of 0.996. >0.996. Recovery studies were carried out on spiked shallot blank samples, at two concentration levels (0.4 and 2.0mg/kg) with three replicates performed at each level. Mean recoveries of 97.2-104.9% with RSDs of 1.3-2.7% were obtained. The method is demonstrated to be suit- able for the determination of chlorothalonil in shallot. The dissipation rates of chlorothalonil were described using first-order kinetics, and its half-life was 2.8days. Based on the dissipation pattern of the pesticide residues, the pre-harvest residue limit (PHRL) was also calculated. Residues were confirmed via mass spectrometry. Copyright © 2012 John Wiley & Sons, Ltd.