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 c hemical ionization (APCI), and gas chromatography-mass spectrometry (GC-MS) with electron impact ionization (EI), are compared for the determination o f eight pesticides in oranges. Seven of the selected pesticides, chlorpyrip hos, chlorpyriphos-methyl, imazalil, alpha and beta -endosulfan, endosulfan sulphate and dicofol, are commonly determined by GC whereas one, thiabenda zole, 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 c ontrast, a high degree of fragmentation is reported with GC-MS. Both techni ques were applied to oranges, which had been previously extracted with ethy l acetate and anhydrous sodium sulphate. The data indicate equivalent defec tion limits that range from 0.01 to 0.1 mg kg(-1) and similar degree of spe cificity. Mean recoveries ranged from 82% for alpha -endosulfan to 96% for imazalil, with relative standard deviation ranging from 7 to 17%.