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 t hree benzoylurea insecticide residues (diflubenzuron, flufenoxuron and hexa flumuron) in citrus fruits is described. Residues were successfully separat ed on a C-18 column by methanol/water gradient elution, Detection was by ne gative-ion, selected-ion monitoring atmospheric pressure chemical ionizatio n-mass spectrometry (APCI-MS); the main ions were [M-H](-), and the seconda ry fragment ions were [M-H-HF](-). Useful confirmatory information can thus be obtained at low extraction voltages from losses of IPP. Detection limit s for standard solutions were 10 fg injected and good linearity and reprodu cibility were obtained. The optimum LC/APCI-MS conditions were applied to t he analysis of benzoylureas in oranges. Samples were extracted using matrix solid phase dispersion (MSPD), in which orange samples were homogenized wi th Cs, placed onto a glass column and eluted with dichloromethane, Detectio n limits of 2 mu g kg(-1) in the crop were obtained. Average recoveries fro m 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 benzoylu reas were sometimes detected at concentration levels lower than maximum res idue limits. Copyright (C) 2000 John Wiley & Sons, Ltd.