Comparison of solid-phase extraction sorbents for cleanup in pesticide residue analysis of fresh fruits and vegetables

Sample extracts of various commodities, obtained using the US Food and Drug Administration (acetone extraction) and Canadian Pest Management Regulatory Agency (acetonitrile extraction) methods for pesticides were subjected to cleanup with solid phase extraction (SPE) columns. Graphitized carbon black (GCB), octadecylsilyl (C-18), strong anion exchange (SAX), aminopropyl (-NH2), and primary secondary amine (PSA) SPE columns were evaluated. The relative sample cleanup provided by these SPE columns was evaluated using gas chromatography with electron capture, flame photometric, and mass spectrometric detection. The -NH2 and PSA columns were found to provide the most effective cleanup, removing the greatest number of sample matrix interferences. The GCB columns removed most of the visible plant pigment in the extracts, but did little to eliminate the fatty acid matrix interferences "seen" by the detectors. Likewise, the C-18 and SAX columns did little to eliminate matrix interferences. Using an acetone extraction followed by a PSA cleanup, both polar and nonpolar pesticides present in samples at 1.0 ng/g could be recovered.