An electrochemical detector cell for open tubular liquid chromatography and capillary electrophoresis

Capillary-electrode alignment by an optical-fiber connector for amperometric detection in capillary electrophoresis

We describe here an electrochemical cell ideal for routine analysis of CE-EC experiments (capillary electrophoresis coupled with electrochemical detection). The cell was modified from a fiber-optic connector, named MT, which allowed frequent change and fast alignment between a pair of 4-strand fiber ribbons. The relative standard deviations of the current response and migration time for 100 microM dopamine were, respectively, 3.7 and 0.5% in five repetitive routines of disconnecting, polishing, and assembling the CE cell. The time required for alignment of the separation capillary and the working electrode was < 10 s, once all components were assembled in an MT fiber-optic plug. These features enabled CE-EC users to polish the working electrode and reassemble the EC cell as in HPLC-EC. However, to accommodate the channel dimensions of the commercially available MT, a special order capillary with outer diameter of 125 microm is necessary at this stage.

A handy detection cell for end-column electrochemical detection in capillary electrophoresis

A handy and simple detection cell was constructed using a mixing joint for end-column electrochemical detection in capillary electrophoresis (CE). The cell allows for positioning of the working electrode at the end of the separation capillary without the aid of micropositioners. The design facilitates the exchange of electrodes and capillaries without the need to refabricate the entire capillary-electrode setup. The cell can be assembled in a short period of time. Alignment with the joint screw proved to be reproducible for working electrodes of copper and gold. The advantages of reduced time and low cost make the device very attractive for the routine analysis of electroactive species, such as carbohydrates and their derivatives, purine bases and nucleosides, amino acids, and catecholamines etc. by CE with electrochemical detection.

A new capillary electrophoresis end-column amperometric detection system without the need for capillary/electrode alignment

A self-aligning end-column amperometric detection system for capillary electrophoresis was constructed. In this system, the electrode and capillary were exchanged easily and the capillary/electrode alignment procedure is not required. Gold, gold/mercury amalgam, copper and carbon fiber could be used as the working electrode. The principle is in the use of two disk holders with the capillary and the electrode in the center, so that by inserting the disk holders into a groove in the working electrode port, the capillary and the electrode are automatically aligned and the distance between the capillary and the electrode is assured at 0.24 mm. The relative standard deviation obtained using five different gold/mercury amalgam microdisk electrodes for determination of cysteine was 1.5% for the migration time and 3.3% for the electrophoretic peak current. The simple and convenient system was attractive for the routine analysis by capillary electrophoresis with electrochemical detection. The system was applied to the determination of promethazine hydrochloride in human serum.

Applications of capillary electrophoresis with electrochemical detection in pharmaceutical and biomedical analyses

As a high efficiency separation technique, capillary electrophoresis has been widely used in various fields of analytical science. This review discusses the applications of electrochemical detection systems combined with capillary electrophoresis in pharmaceutical and biomedical analysis. These detection methods mainly involve amperometric detection but also include conductivity detection and potentiometric detection. Its applications in the field are divided into six parts, including catechol compounds, thiols, amino acids and peptides, carbohydrates, general pharmaceuticals, and other related compounds. A relatively detailed discussion is described for each compound under the current studied. On this basis, we have suggested several conceivable directions for capillary electrophoresis with electrochemical detection in the future.

Subnanoliter volume wall-jet cells combined with interdigitated microarray electrode and enzyme modified planar microelectrode

Miniaturized wall-jet type flow cells with an active volume of 0.042-15 nL were fabricated for use as highly sensitive electrochemical detectors for capillary electrophoresis/electrochemical detection and small on-line enzyme sensors. The cells consisted of three glass plates and a fused-silica capillary. Two of the plates had microfabricated flow channels and guide trenches for the capillary and working, reference, and counter electrodes. The other plate had a film electrode. When an interdigitated microarray electrode (total area, 66 microm x 64 microm; bandwidth and gap, 2 microm) was installed in the flow cell, the redox cycling enhanced the current at flow rates of less than 100 nL/min even though there were only eight pairs of microbands. A sharp dopamine peak enhanced by the redox cycling was observed when the cell was used for capillary electrophoresis. A square film electrode modified with glutamate oxidase and Os-poly(vinylpyridine) containing HRP was also installed in the flow cell and used to measure neurotransmitter release from cultured nerve cells. When the flow rate was relatively high, the response time of the modified electrode was comparable to that of a cylindrical carbon fiber electrode (33 microm o.d.) modified with the same enzyme and mediator. We observed a transient cathodic current response assigned to the glutamate release with the electrode in the flow cell in a suction mode measurement when we stimulated cultured nerve cells electrically with a dual microelectrode.

End-column amperometric detection in capillary electrophoresis: influence of separation-related parameters on the observed half-wave potential for dopamine and catechol

Capillary electrophoresis (CE) was coupled to a micro-electrode-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 microns. 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 microA, 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).

Electrochemical detection in capillary electrophoresis

Recent advances in the design and application of electrochemical detection (EC) systems in capillary electrophoresis (CE) are reviewed, with the objective of providing the non-electrochemist with a state-of-the-art picture of CEEC instrumentation and an overview of the primary analytes and samples for which the technique is best suited. In particular, instrument innovations designed to aid in decoupling the CE and EC systems electrically and in aligning them physically are described in detail. In addition, CEEC applications are summarized for four specific analyte groups: catecholamines, thiols and disulfides, amino acids, and carbohydrates. On this basis, it is clear that EC techniques have reached a stage where they are already having a significant impact on CE usage in selected areas of analysis. Continued developments with respect to new electrode materials and electrode configurations promise to broaden this impact further.