Electrode configuration electrochemical detector

Guijt et al. [69] reported four-electrode capacitively coupled conductivity detection in NCE. The glass microchip consisted of a 6 cm etched channel (20 x 70 pm cross-section) with silicon nitride covered walls. Laugere et al. [70] described chip-based, contactless four-electrode conductivity detection in NCE. A 6 cm long, 70 pm wide, and 20 pm deep channel was etched on a glass substrate. Experimental results confirmed the improved characteristics of the four-electrode configuration over the classical two-electrode detection set up. Jiang et al. [71] reported a mini-electrochemical detector in NCE,... 

Figure 3.28 Common configurations of electrochemical detectors for CE microchips, based on different capillary/working-electrode arrangements and the position of the electrode (w) relative to the flow direction (a) flow by (using two plates) (b) flow onto (with the surface normal to the flow direction) (c) flow through (with the detector placed directly on the channel exit). (Reproduced with permission from Ref. 78.)...

Figure A. Column end-assembly configured for mlcrovolcammecric electrochemical detector AE, auxiliary electrode CA, cartridge holder CH, column holder CM, Column EH, electrode holder FR, frit MM, micromanipulator PP, piezoelectric positioner RE, reference electrode SC screw cap WE, working electrode. (Reproduced from ref. 11. Copyright 1988 American Chemical Society.)...

The hydrodynamically well-defined conditions of flow systems are an ideal environment for electrochemical detectors, resulting in enhanced performance characteristics. The surface sensing properties of most electrochemical methods require particular attention in the construction of suitable flow-through cells. Efficient and repeatable mass transport toward the electrode surface is necessary, and dead volumes should be small. Various flow-through cells have been designed for electrochemical detection, all of which can be derived from the basic configurations depicted in Figure 4. 

Figure 1 Illustrations of electrochemical detector configurations coupled to capillary liquid chromatography columns. (A) End-column or wall jet electrode configuration with the working electrode positioned proximal to the fused silica capillary outlet. (B) On-column electrode showing a cylindrical carbon fiber positioned in the fused silica capillary outlet forming a thin annular layer between the fiber surface and the inner capillary wall.

Basically, an electrochemical detector for HPLC is a flow electrochemical cell which contains all of its basic elements (working, reference and auxiliary electrodes, holder, and connections) adapted to the experimental conditions expected in the chromatographic separations. The characteristics of the materials used for the holder and the electrodes construction must be compatible with typical mobile phases, working pressures, and temperatures employed in HPLC whereas the geometric configuration must provide an easy coupling... 

FIGURE 8 Electrochemical detector cell (Bioanalytical Systems, Inc.), (a) Diagram of the flow cell. A = auxiliary electrode, W = working electrode. R = reference electrode, (b) Dual thin-layer working electrodes in parallel (1) and series (2) configurations. [From Bratin K., and Kissinger, P. T. (1981). J. Liq. Chromator. 4, 321-57. Reprinted with permission from Marcel Dekker, Inc.]... 

Another interesting method of amperometric detection for LC is dualelectrode electrochemical detection. Instead of a single WE, one can place two WEs in series, parallel to or opposite each other. The series configuration is mostly used, mainly in the collection mode, i.e., the electroactive substance entering the detector is converted at the upstream (generator) electrode into a product that either is or is not detected at the downstream (indicator) electrode, depending on the potential of the latter. Hoogvliet et al.137,162 were easily able... 

Fig. 18b.1. Electrochemical cells and representative cell configurations, (a) Schematic diagram of a cell-potentiostat system, (b) Typical laboratory cell with Hg-drop electrode and drop knocker, (c) Voltammetric cell as detector at the end of a high-performance liquid chromatographic column, (d) A two-electrode (graphite) chip cell for biosensor development, (e) Three-electrode chip cells on a ceramic substrate for bioanalytical work.

The portable instrumentation and low power demands of stripping analysis satisfy many of the requirements for on-site and in situ measurements of trace metals. Stripping-based automated flow analyzers were developed for continuous on-line monitoring of trace metals since the mid-1970s [16,17]. These flow systems involve an electrochemical flow detector based on a wall-jet or thin-layer configuration along with a mercury-coated working electrode, and downstream reference and counter electrodes. 

Carbon nanotubes, especially SWNTs, with their fascinating electrical properties, dimensional proximity to biomacromolecules (e.g., DNA of 1 nm in size), and high sensitivity to surrounding environments, are ideal components in biosensors not only as electrodes for signal transmission but also as detectors for sensing biomolecules and biospecies. In terms of configuration and detection mechanism, biosensors based on carbon nanotubes may be divided into two categories electrochemical sensors and field effect transistor (FET) sensors. Since a number of recent reviews on the former have been published,6,62,63 our focus here is mostly on FET sensors. 

Electrochemical detection offers also great promise for CZE microchips, and for other chip-based analytical microsystems (e.g., Lab-on-a-Chip) discussed in Section 6.3 (77-83). Particularly attractive for such microfluidic devices are the high sensitivity of electrochemical detection, its inherent miniaturization of both the detector and control instrumentation, low cost, low power demands, and compatibility with micromachining technologies. Various detector configurations, based on different capillary/working-electrode... 

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