Multiresidue screening methods for the determination of pesticides in plant materials

The determination of pesticides in plant materials and related matrices is of great importance in environmental chemistry. To meet the increasing requirements for fast and reliable analytical procedures, a multiresidue screening method for the determination of pesticides in various plant materials has been developed. For samples with a low fat content, preconcentration of the analytes was carried out by solid-phase extraction (SPE) after extracting the samples with an acetone-water mixture; the ethyl acetate eluate was further cleaned up using Florisil. Gas chromatography with electron-capture detection or mass spectrometric detection in the negative chemical ionization mode (GC-NCI-MS) was employed for the separation and quantification of the pesticides. The first step of this procedure had to be modified for materials containing high amounts of fat, such as olive oil or corn germ oil. In this case, 0.5 g of these samples were blended with silica particles, which were then placed over a layer of poly(styrene-divinylbenzene) particles in an SPE cartridge and eluted with acetonitrile saturated with n-hexane. The eluate was dried with sodium sulfate, cleaned up with Florisil and determined by GC-NCI-MS. Using this method, no interferences were encountered in the matrices investigated. The method has been tested for various plant materials spiked with up to 28 pesticides and the recoveries obtained were generally in the range of 85 to 110%, with relative standard deviations below 7%. (C) 1999 Elsevier Science B.V. All rights reserved.