Use of 3-(p-carboxybenzoyl)quinoline-2-carboxaldehyde to label amino acids for high-sensitivity fluorescence detection in capillary electrophoresis

Detection of amino acids by laser-induced fluorescence capillary electrophoresis can be achieved by using a fluorogenic reagent, 3-(p-carboxybenzoyl)quinoline-2-carboxaldehyde (CBQ). This reagent does not fluoresce unless it has reacted with a primary amine to form an isoindole derivative. Using a sheath flow cuvette as a post-column detector and excitation by the 488-nm argon ion laser line we obtain a limit of detection of 9.0 zeptomoles (1 zeptomol = 10^-21 mol) for the CBQ-arginine derivative, which is 150 times better than previously reported. We also investigate and optimize the derivatization reaction by successfully labeling arginine concentrations as low as 10 ^-7 M. CBQ-arginine derivatives from lower concentrations of this amino acid cannot be detected due to secondary reactions of CBQ and cyanide, which generate background peaks that swamp the CBQ-amino acid peak.