Comparison of gas and liquid chromatography coupled to mass spectrometry for the residue analysis of pesticides in oranges

Liquid chromatography mass spectrometry (LC-MS) with atmospheric pressure chemical ionization (APCI), and gas chromatography-mass spectrometry (GC-MS) with electron impact ionization (EI), are compared for the determination of eight pesticides in oranges. Seven of the selected pesticides, chlorpyriphos, chlorpyriphos-methyl, imazalil, alpha and beta -endosulfan, endosulfan sulphate and dicofol, are commonly determined by GC whereas one, thiabendazole, can only be directly determined by LC. Primary ions [M-H](-) or [M-Cl+O](-) are obtained using LC-APCI-MS in negative ionization (NI) mode. In contrast, a high degree of fragmentation is reported with GC-MS. Both techniques were applied to oranges, which had been previously extracted with ethyl acetate and anhydrous sodium sulphate. The data indicate equivalent defection limits that range from 0.01 to 0.1 mg kg(-1) and similar degree of specificity. Mean recoveries ranged from 82% for alpha -endosulfan to 96% for imazalil, with relative standard deviation ranging from 7 to 17%.