Solid-phase extraction cleanup of tomato samples for the determination of pesticide residues by gas chromatography-electron capture detection

Abstract

Extracts of tomato samples, obtained using acetone solvent followed by liquid–liquid partition with a mixture of dichloromethane and light petroleum (40–60°C), were subjected to cleanup with solid-phase extraction (SPE) columns for the simultaneous multiclass determination of 12 pesticides with different physicochemical properties (log P ow = 0.7 to > 6). Silica, aminopropyl (NH2), graphitized carbon black (GCB), octadecyl (C-18) with GCB and the mixed-mode SAX/PSA (SPE) columns were evaluated. The sample cleanup provided by these columns was evaluated using gas chromatography with electron capture detection. The mixed-mode SAX/PSA columns were found to provide the most effective cleanup, along with the (NH2) columns, removing the greatest number of sample matrix interferences. The GCB sorbents also remove pigments but do not remove noticeable chromatographic interferents. The silica columns did little to eliminate the matrix effect for the compound dimethoate. Likewise, the C-18 in combination with the GCB sorbents did little to eliminate matrix interferences.