End-Column Amperometric Detection in Capillary Electrophoresis:  Influence of Separation-Related Parameters on the Observed Half-Wave Potential for Dopamine and Catechol

• Published in: Analytical chemistry (Washington) 1999-02, Vol.71 (3), p.544-549
• Main Authors: Wallenborg, Susanne R, Nyholm, Leif, Lunte, Craig E
• Format: Article
• Language: English
• Subjects: Analytical chemistry; Analytical, structural and metabolic biochemistry; Biological and medical sciences; Catechols - analysis; Catechols - chemistry; Chemistry; Chromatographic methods and physical methods associated with chromatography; Dopamine - analysis; Dopamine - chemistry; Electrochemistry - methods; Electrophoresis, Capillary - methods; Exact sciences and technology; Fundamental and applied biological sciences. Psychology; Non peptidic neurotransmitters, polyamines; Other biological molecules; Other chromatographic methods
• ISSN: 0003-2700; 1520-6882
• DOI: 10.1021/ac980737v

Capillary electrophoresis (CE) was coupled to a microelectrode-based end-column amperometric detector. The influences of separation voltage, CE buffer concentration, and capillary-to-electrode distance on the observed hydrodynamic voltammetry of dopamine and catechol were studied using a separation capillary with an i.d. of 25 μm. It was found that an increased CE voltage, increased buffer concentration, or decreased capillary-to-electrode distance resulted in a positive shift of the observed half-wave potentials for both dopamine and catechol. At a constant separation current of 1.6 μA, the observed half-wave potential was found to increase with applied separation voltage. Furthermore, when experiments were carried out with a platinum quasi-reference electrode instead of a Ag/AgCl reference electrode, similar shifts in half-wave potential were observed. These results indicate that the observed shifts are an effect of the separation voltage rather than the separation current or a change in the reference potential. The characteristics of end-column detection with and without a fracture decoupler were compared. It was found that the effects of separation voltage, CE buffer concentration, and capillary-to-electrode distance were minimized by the use of a decoupling device. The observed half-wave potentials for dopamine and catechol were more positive when a CE capillary without a decoupler was employed compared to when a decoupler was used. Additionally, using the fracture decoupler, the observed half-wave potentials for both dopamine and catechol were approximately the same as when no CE voltage was applied (i.e., when the hydrodynamic voltammograms were recorded under flow injection conditions).