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

Abstract

A surface-sampling technique of liquid extraction surface analysis (LESA) was coupled with capillary electrophoresis (CE) to determine organophosphorous pesticides, including glufosinate-ammonium, aminomethylphosphonic acid, and glyphosate on the external surface of a fruit such as an apple. Without any sample pretreatment, the analytes sprayed on the surface of a half apple were directly extracted into a liquid microjunction formed by dispensing the extractant from the inlet tip of a separation capillary. The extraction efficiency was enhanced by repeating the 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 with CE-laser induced fluorescence (LIF) detection. The developed LESA-CE/LIF carries out quantitative analysis in a convenient and rapid manner, which is made possible since the extraction and separation of analytes can be performed in-line. The limits of detection for glufosinate-ammonium, aminomethylphosphonic acid, and glyphosate with LESA-CE/LIF were 2.5, 1, and 10 ppb, respectively, which are at least 20 times lower than the tolerance established by the U.S. Environmental Protection Agency. Thus, we demonstrated that LESA-CE is a quite sensitive and convenient method to determine analytes on sample surfaces avoiding the dilution problem from sample pretreatment procedures including homogenization of bulk samples.