Potential possibilities of long-chain ionic liquids based on imidazole (1-dodecyl-3-methylimidazolium chloride and 1-cetyl-3-methylimidazolium chloride) for online sample concentration techniques (field-amplified sample stacking, head-column field-amplified sample stacking, and sweeping) of catecholamines were studied in both capillary zone electrophoresis and micellar electrokinetic chromatography. The use of a high-conductivity sample matrix in sweeping was found to significantly increase the separation efficiency of analyte up to 2 × 10⁶ theoretical plates per meter and remarkably reduce limits of detection for catecholamines up to 50 ng/mL. This approach was shown to be suitable for the determination of trace amounts of catecholamines in biological fluids.