Abstract: A new idea of solvent transfer technique was developed and applied to determine 283 pesticide residues in garlic by gas chromatography-mass spectrometry (GC-MS) (method I), and the other method using normal phase silica/selective elution technique was applied to determine 6 pesticide residues with strongly polar in garlic by gas chromatography (method II). For the method I, the residues were extracted from homogenized tissue with acetonitrile-water, separated with liquid-liquid partition; the clear supernatant was purified by solvent transfer technique and solid phase extraction (Envi-18 and LC-NH2 columns), then was analyzed by GC-MS. For the method II, the residues were extracted from homogenized tissue using ethyl acetate and sodium sulfate assisted by ultrasonication. The supernatant was purified by solid phase extraction (primary secondary amine (PSA) powder and LC-Si column) prior to GC analysis. The determination was performed by using selected ion monitoring (SIM) mode in GC-MS method and flame photometric detector (FPD) in GC method, then external standard method was used in the quantification. Under the optimal conditions, the detection limits for the two methods (S/N≥10) of pesticides were 0.01~0.05 mg/kg, the recoveries carried out by the addition of standards of 0.01~0.20 mg/kg were 52%~163%, among which the recoveries for 88% pesticides were between 70% and 120%; the recoveries of the method II were 70%~111%; while the relative standard deviations were 2.4%~18% and 3.2%~9.3%, respectively. The model of solvent transfer technique and the sensitivity improvement of GC-MS was also studied. The methods are easy, fast, more sensitive, and can meet the requirement of the multiresidual analysis in garlic.

Key words: garlic, gas chromatography-mass spectrometry (GC-MS), multiresidual analysis, pesticides, sample pretreatment, gas chromatography (GC), sensitivity