Methanol plug assisted sweeping-micellar electrokinetic chromatography for the determination of dopamine in urine by violet light emitting diode-induced fluorescence detection

The use and limitations of a methanol plug assisted sweeping-micellar electrokinetic chromatography (sweeping-MEKC) method is described. Using naphthalene-2,3-dicarboxaldehyde (NDA)-labeled dopamine as a model compound, this new method was also used in the determination of dopamine in actual urine samples. An inexpensive violet light emitting diode (LED) was used for the light source, because this is suitable for fluorescence excitation. The number of theoretical plates of the analyte was determined to be ∼1 × 105 and ∼2 × 105 by means of MEKC and sweeping-MEKC and this was improved to ∼1 × 106 when the methanol plug assisted mode was applied. In addition, the detection limit of NDA-labeled dopamine was determined to be 9.1 × 10−7 and 1.2 × 10−8 M by means of MEKC and sweeping-MEKC and this was improved to 4.7 × 10−9 M when the methanol plug assisted sweeping-MEKC mode was applied.