Violet light emitting diode-induced fluorescence detection combined with on-line sample concentration techniques for use in capillary electrophoresis

The first application of a violet light-emitting diode (LED) for fluorescence detection in capillary electrophoresis (CE) is described. The utility of violet LED (peak emission wavelength at 410 nm, ∼2 mW) for fluorescence detection is demonstrated by examining reserpine and dopamine-labeled NDA (naphthalene-2,3-dicarboxaldehyde), respectively. The detection limit for reserpine was determined to be 2.5 × 10^-6 M by normal micellar electrokinetic capillary chromatography (MEKC) and this was improved to 2.0 × 10^-9 M and 2.0 × 10^-10 M when sweeping-MEKC and cation-selective exhaustive injection (CSEI)-sweep-MEKC techniques were applied, respectively. In addition, the detection limit of NDA-labeled dopamine was determined to be 6.3 × 10^-6 M by means of normal MEKC and this was improved to 3.0 × 10^-8 M when the sweeping-MEKC mode was applied.