Liquid chromatography/atmospheric pressure chemical ionization-mass spectrometric analysis of benzoylurea insecticides in citrus fruits

A liquid chromatography (LC) method for the quantitative determination of three benzoylurea insecticide residues (diflubenzuron, flufenoxuron and hexaflumuron) in citrus fruits is described. Residues were successfully separated on a C-18 column by methanol/water gradient elution, Detection was by negative-ion, selected-ion monitoring atmospheric pressure chemical ionization-mass spectrometry (APCI-MS); the main ions were [M-H](-), and the secondary fragment ions were [M-H-HF](-). Useful confirmatory information can thus be obtained at low extraction voltages from losses of IPP. Detection limits for standard solutions were 10 fg injected and good linearity and reproducibility were obtained. The optimum LC/APCI-MS conditions were applied to the analysis of benzoylureas in oranges. Samples were extracted using matrix solid phase dispersion (MSPD), in which orange samples were homogenized with Cs, placed onto a glass column and eluted with dichloromethane, Detection limits of 2 mu g kg(-1) in the crop were obtained. Average recoveries from citrus fortified with approximately (25-1000 mu g kg(-1)) ranged from 87 to 102%. The method was applied to held-treated orange samples and benzoylureas were sometimes detected at concentration levels lower than maximum residue limits. Copyright (C) 2000 John Wiley & Sons, Ltd.