Electrochemical detector, diagram system

FIGURE 7.10 Block diagram of a basic electrochemical detector. All three electrodes are controlled by a regulated power supply coupled to a potentiometer and a series of amplifiers. The output from the electrodes is fed into a data acquisition system. 

Fluorescence detection, because of the limited number of molecules that fluoresce under specific excitation and emission wavelengths, is a reasonable alternative if the analyte fluoresces. Likewise, amperometric detection can provide greater selectivity and very good sensitivity if the analyte is readily electrochemically oxidized or reduced. Brunt (37) recently reviewed a wide variety of electrochemical detectors for HPLC. Bulk-property detectors (i.e., conductometric and capacitance detectors) and solute-property detectors (i.e., amperometric, coulo-metric, polarographic, and potentiometric detectors) were discussed. Many flow-cell designs were diagrammed, and commercial systems were discussed. 

Fig. 11.12. Schematic diagram of a column-switching HPLC system. V-l, V-2, and V-3 switching valves. The position of °—c means position 1, and ° ° is position 2. P-1 and P-2 pumping system at 0.2 mL min-1 flow rate. Detector electrochemical detector with diamond electrodes. Column-1 and Column-2 Inertsil ODS-3. Loop 500 pL. A Mobile phase of 60% methanol-water containing 0.5% phosphoric acid.

Fig. 20. Block diagram of HPLC column switching system with electrochemical detection. L, sample loop 7125 and 7010, injection valves W, waste PC, precolumn AC, analytical column AMP, electrochemical detector REC, strip chart recorder PD, pulse dampers PS, presaturator columns.

Fig. 7. Details of LC Electrochemical Detector. (A) Relationship of LC column and outflow to electrode system (B) enlargement of detector cell and graphite paste working electrode. (Diagrams based on equipment from Bioanalytical Systems.)...

Figure 3.18 Schematic diagram of a chip-based CE system with an external electrochemical detector.

FIGURE 2.10 Schematic diagram of the SIA system for the evaluation of total antioxidant capacity with an in-house flow-through electrochemical detector (ECD) (1.9 cm width X 5.1 cm length x 2.3 cm height). CE, counter electrode WE, working electrode RE, reference electrode. (Reprinted with permission from Chan-Eam, S. et al. 2011. Talanta 84 1350-1354.)... 

FIGURE 31,14 (a) Schematic diagram of an FI system with the electrochemical detection of online generation of ABTS +. (b) Construction of a flow-through electrochemical detector, (c) FI signals obtained for water-soluble AOXs. The concentration of injected antioxidant solutions 250 pM for Tr, Asc, and uric acid 220 pM for reduced glutathione. (Modified from Milardovic, S., I. Kerekovic, and V. Rumenjak. 2007. Food Chem. 105 1688-1694.)... 

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.]... 

Fig. 7.2. Flow diagram of standard laboratory instrumentation used for chromatography with electrochemical or spectrophotometric detection of metal dithiocarbamate complexes. 1 = chromatographic solvent, 2 = solvent delivery system, 3 = it jec-tion system, 4 = guard column, 5 = separator column, 6 = suppressor column, 7 = spectrophotometric detector, 8 = electrochemical detector, 9 = readout device, 10 = microprocessor. Reproduced by courtesy. J. Liquid Chromatog. 6 (1983) 1799.

Fig. 3. Diagrams of electrochemical cells used in flow systems for thin film deposition by EC-ALE. A) First small thin layer flow cell (modeled after electrochemical liquid chromatography detectors). A gasket defined the area where the deposition was performed, and solutions were pumped in and out though the top plate. Reproduced by permission from ref. [ 110]. B) H-cell design where the samples were suspended in the solutions, and solutions were filled and drained from below. Reproduced by permission from ref. [111]. C) Larger thin layer flow cell. This is very similar to that shown in 3A, except that the deposition area is larger and laminar flow is easier to develop because of the solution inlet and outlet designs. In addition, the opposite wall of the cell is a piece of ITO, used as the auxiliary electrode. It is transparent so the deposit can be monitored visually, and it provides an excellent current distribution. The reference electrode is incorporated right in the cell, as well. Adapted from ref. [113],...

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 LD-17 is an electrochemical voltametric detector operating under diffusion-controlled conditions.) The effluent H2S concentration never exceeded 250 ppm and was usually less than 50 ppm. Evolution profiles were recorded by a strip-chart recorder. Figure 1 shows the schematic diagram of the H2S evolution system. 

A schematic diagram of a working FIA system is shown in Fignre 9.9. FIA can be nsed with many types of detector incinding electrochemical, e.g. pH probes, ISEs and condnc-tivity, and spectroscopic, e.g. UV-Vis, infrared and flnorescence. Diode array detectors allow the monitoring of many components simnltaneonsly, and conpled with chemometrics can be a very fast and information-rich technique. The detector itself should have a small cell volume to avoid undue dispersion. 

The basic instrumentation of flow injection systems consists of the manifold, a pump for the transport of the reagent, rotary sample injection valves, a flow-through cell, and a detector [6], which can be chemiluminescence-, mass spectrometric-, or electrochemical-based, among other possibilities. For example Figure 10.2 shows the block diagram of a flow injection system coupled to chemiluminescence detection. The sample is introduced into the flow injection analysis system via the injection valve or via an autosampler, while the carrier and reagent streams are pushed forward to the detector by the pumps. 

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