Sunkyung Jeong, Doo Soo Chung
Department of Chemistry, Seoul National University, Seoul 08826, Korea
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Liquid extraction surface analysis (LESA) has the advantage of directly sampling analytes on a surface, thus avoiding unnecessary dilution by homogenization of the bulk sample commonly practiced in solid sample analysis. By combining LESA with capillary electrophoresis (CE), the additional advantage of separating analytes before detection can be accomplished. As a representative application of LESA-CE to a solid surface sample, non-infiltrative pesticides on the apple skin were analyzed. When non-infiltrative pesticides are applied to fruits such as apples, they remain on the fruit skin without being translocated to the fruit pulp. First, glufosinate-ammonium and glyphosate on the apple skin were directly extracted and injected into the separation capillary. After in-capillary derivatization with a fluorophore NBD-F, the pesticides were analyzed by CE-LIF. Secondly, three pesticides, chlorantraniliprole, kresoxim-methyl, and pyraclostrobin on the apple skin were analyzed by LESA-CE. For these water-insoluble neutral analytes, micellar electrokinetic chromatography combined with an on-line sample stacking method, analyte focusing by micelle collapse was employed. In addition, using a commercial CE instrument, the LESA process was performed much faster and more reliably compared to LESA-CE using a homemade CE setup. Thirdly, to analyze both cations and anions on a solid surface with a single run of a reasonable detection time, two contactless capacitively coupled conductivity detectors (C4D) were placed on a single capillary. After LESA using the inlet of a coated fused silica capillary having a weak but reversed EOF, the extracts were placed between the two C4Ds. When a reverse electric field is applied, the cations and anions migrated in the opposite directions, and were quickly detected with the C4D located in each direction. The ionic composition of a lithium battery anode surface was investigated by this LESA-CE/2C4D. The developed LESA-CE is promising for the analysis of biological surfaces of cells and tissue as well as technical surfaces.
The authors acknowledge the supports from the National Research Foundation of Korea (2021R1F1A1045947).
