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An online sandwich derivatization and stacking strategy using capillary electrophoresis was developed and successfully applied to the preconcentration of multi-amino acids in two functional food samples. Amino acids were derived with 4-Chloro-7-nitro-1, 2, 3-benzoxadiazole (NBD-Cl) to make the new compounds with chromophore in the stacking process, then the derivatives were stacked by on-column sample preconcentration and detected at 475 nm UV wavelength. The novel sandwich injection sequence was amino acids, NBD-Cl, and amino acids separately. Additionally, the running buffer was 40 mM borax buffer (pH = 9.0). A succession of derivatization and stacking conditions were optimized, including buffer concentration, pressure, NBD-Cl injection time, waiting time, matrix concentration, and sample injection time. In the appropriate range, good linearity values (R |
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