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

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Abstract
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.