Abstract: A gas chromatography-negative chemical ionization mass spectrometric (GC-NCI/MS) method has been developed for analyzing 14 pesticide residues in sulfur-containing vegetables (scallion, garlic, garlic bolt, leek, etc.). The samples were first heated in a microwave oven to eliminate most of the sulfur-containing interfering impurities and then extracted with acetonitrile. The extracts were further cleaned-up by gel permeation chromatography (GPC) and a primary-secondary amine (PSA) cartridge. The target analytes were determined using GC-NCI/MS in the selected ion monitoring (SIM) mode. The recoveries of all the pesticides (at spiked level of 50 μg/kg) were from 49.2% to 113.1% with the relative standard deviations between 1.42% and 8.70%. The detection limits (S/N=3) were in the range of 0.5-10.0 μg/kg. The method is selective without interference and suitable for the determination and confirmation of pesticides in the sulfur-containing vegetables.

Key words: negative chemical ionization (NCI), pesticide residues, sulfur-containing vegetables , gas chromatography-mass spectrometry (GC-MS)