Matrix solid-phase dispersion extraction and determination by high-performance liquid chromatography with fluorescence detection of residues of glyphosate and aminomethylphosphonic acid in tomato fruit

A method based on matrix solid-phase dispersion (MSPD) is described for the quantitative extraction of glyphosate and its major metabolite aminomethylphosphonic acid (AMPA) from tomato fruit. After application of 120 microL of HNO3 1M to the sample, the dispersion column was packed with 0.5 g of sample blended into 1 g of NH2-silica. Two aqueous fractions were obtained. First, AMPA was eluted from the column using deionized water (F1), and then a NaH2PO4 0.005 M solution was used for the elution of glyphosate (F2). Cleanup of F1 and F2 was made by ion exchange chromatography on a SAX anion exchange silica. Determination was done by HPLC with fluorescence detection after precolumn derivatization with 9-fluorenylmethylchloroformate (FMOC-Cl). Mean recoveries calculated at fortification levels of 0.5 microg/g for glyphosate and 0.4 microg/g for AMPA were 87% and 78%, respectively. The relative standard deviations (n=7) for the total procedure were 10% and 16%. Detection limits were 0.05 microg/g for glyphosate and 0.03 microg/g for AMPA.