Microwave pretreatment and gas chromatography–mass spectrometry determination of herbicide residues in onion

A rapid multi-residue method was developed for the determination of 16 herbicides in onion. The analytical procedure was based on preventing formation of sulfur-containing compounds in onion by microwave inactivation of the enzyme alliinase. The onion samples which had been pretreated were extracted with acetonitrile and cleaned by solid-phase extraction. The herbicide residues in onion were detected by gas chromatography/mass spectrometry with selected ion monitoring. The recoveries of 16 herbicides ranged from 69.2% to 105.0% with the relative standard deviations (RSD) below 10.7%. The limit of quantitation (LOQ) ranged from 0.003 to 0.015 mg kg−1. The method was applied to the analysis of herbicide residues in onion samples.