Determination of glyphosate residues in plants by precolumn derivatizationand coupled-column liquid chromatography with fluorescence detection

A rapid method was developed for the trace-revel determination of glyphosat e in olives. After extraction of the glyphosate with water-dichloromethane and simultaneous removal of the olive oil, an aliquot of the aqueous extrac t is derivatized with 9-fluoroenylmethyl chloroformate (9-fluorenylmethoxyc arbonyl chloride; FMOC-Cl) to produce a highly fluorescent derivative. A 2 mt aliquot of this extract is injected directly into a coupled-column liqui d chromatography system with fluorimetric detection (LC/LC-FD). The procedu re was validated by recovery experiments at 3 spiking levels; recoveries ra nged from 80 to 97% with relative standard deviations of 3-6%. The limits o f detection and quantitation were estimated to be 0.01 and 0.05 mg/kg, resp ectively. The method was also applied to other plant materials, i.e., tomat o plants, strawberry plants, and pear trees (branches, leaves, and fruits) suspected to be contaminated by glyphosate. In all these cases, the extract ion was performed in aqueous media. The derivatization reaction was modifie d by increasing the FMOC-Cl concentration, to ensure a quantitative reactio n between analyte and reagent in the presence of high levels of coextractiv es, which also react with FMOC-Cl, The final determination was by LC/LC-FD, yielding a rapid, selective, and sensitive method for the determination of glyphosate residues in these samples. The method was tested with real-worl d samples after application of glyphosate to the surrounding area of crops.