A surface-sampling technique called liquid extraction surface analysis (LESA) was coupled with capillary electrophoresis (CE) to determine organophosphorus pesticides, including glufosinate-ammonium, aminomethylphosphonic acid, and glyphosate on the external surface of a fruit such as an apple. A solution containing the pesticides was sprayed onto a solid surface. Without any sample pretreatment, the dried analytes on the surface were directly extracted to a hanging drop of extractant at the inlet tip of a capillary. This extraction was made possible by a liquid microjunction that is formed between the sample surface and the extractant drop. The extraction efficiency was enhanced by repeating steps of dispensing and aspirating the extractant drop. After extraction, the analytes were derivatized in-capillary with a fluorophore 4-flouro-7-nitro-2,1,3-benzoxadiazole and analyzed by CE-laser induced fluorescence detection. The limits of detection of the glufosinate-ammonium and glyphosate with LESA-CE were 20-fold lower than the EPA tolerance levels.

Liquid extraction surface analysis coupled with capillary electrophoresis to determine organophosphorous pesticides on apple

247th National Meeting (2014)

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