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.