Development of near-infrared fluorophoric labels for the determination of fatty acids separated by capillary electrophoresis with diode laser induced fluorescence detection†

Synthesis and characterization of a polymethine cyanine near-infrared (NIR) fluorophoric label for the derivatization and determination of fatty acids separated by capillary electrophoresis are described. The label contains an aromatic amine functionality, which is used to form a covalent linkage with the analyte. Various linking chemistries are explored, including direct amine–acid condensation using dicyclohexylcarbodiimide (DCC) as a carboxyl activating group. Spectrofluorimetry was used to probe the fluorescence efficiency of the label in order to assist in choosing a separation medium for capillary electrophoretic separation. A nonaqueous separation medium for capillary zone electrophoresis was used to provide high quantum efficiency for fluorescence and adequate solubility of fatty acid analytes. Diode laser-induced fluorescence detection following electrophoresis of a simple mixture of labeled fatty acids shows the applicability of this method to biologically relevant carboxylic acid analytes.