Auxiliary reference electrode

To overcome these difficulties one must use a three-electrode cell, which is shown schematically in Figure 8. Here, a third electrode, auxiliary electrode (AE) is inserted together with the working and the reference electrodes. 

Figure 8 The electrode arrangement in a three-electrode cell WE= working electrode RE = reference electrode AE = auxiliary electrode...

Figure 6.17. Schematic diagram of apparatus for galvanostatic measurements P, constant current power supply e, test electrode e2, reference electrode counter (auxiliary)-electrode V, potential-time recording instrument.

Figure 5.11 — Diagram of a generic electrochemical flow-through biosensor using a permselective film coating the surface of the en2yme electrode. RE reference electrode AE auxiliary electrode W waste.

Voltammetry is the second most utilized technique for electronic tongue devices (see Fig. 2.6). It is a d)mamic electroanalytical method, that is, a current flow passes through the measurement cell (z 0). Voltammetry consists of the measurement of current at a controlled potential constant or, more frequently, varying. In the classic three-electrode cell configuration, the current flows between two electrodes, called working and counter (or auxiliary) respectively, while the potential is controlled between the working and a third electrode, the reference (Kissinger and Heineman, 1996). 

W working electrode R reference electrode A auxiliary electrode... 

Because it is not possible to control exactly the amount of sample transferred to the electrode surface, nonrepeatable values of k,i2 will generally be obtained. For this reason, a known amount, rriR, of a third auxiliary reference compound (R) is added so that the sample/reference material mass ratio, m/m, is constant and known. If the voltammetric signal corresponding to the reduction or oxidation of R occurs at potentials sufficiently separated from those at which overlapping peaks of A and B are recorded, the peak current measured for R, ip R), must satisfy... 

Figure 18.3—Principle of ISE measurement of fluoride ions in solution using a double junction reference electrode. The reference electrode is inserted into a separate chamber that contains the auxiliary electrolyte in order to avoid osmosis of KC1 into the sample solution. Also, 1 M KN03 can be used for F , Cl, CN or Ag+ determination. The measurement involves the use of a high impedance millivoltmeter (pH meter type). A version of an all-solid fluoride electrode is shown on the right.

Figure 6.18b depicts the classical three-electrode constant-current experiment. The counter electrode is now replaced by an auxiliary electrode and a reference electrode. The reference electrode enables one to monitor the working electrode potential as a function of time using a high-impedance (zero-cur-rent) measuring device. In many early experiments, carried out on a time scale... 

Figure 9.1 Equivalent circuit of an electrochemical cell. A, Auxiliary electrode R, reference electrode W, working electrode Rc, compensated resistance R , uncompensated resistance Rr, reference electrode impedance Zf, faradaic impedance Cdl, doublelayer capacitance.

Figure 9.3 Stationary solution voltammetry cells, (a) Platinum wire loop auxiliary electrode, (b) reference electrode or reference electrode probe tip, (c) carbon paste working electrode, (d) graphite auxiliary electrode, (e) dropping mercury electrode, (0 platinum wire contact to mercury pool working electrode, (g) nitrogen gas inlet tube, (h) magnetic stirrer, (i) mercury pool working electrode, (j) glass frit isolation barrier.

Figure 9.5 Controlled-potential coulometry cell with a mercury pool working electrode. a, Platinum wire contact to mercury pool working electrode b, mercury pool working electrode c, reference electrode d, auxiliary electrode e, porous Vycor f, sample solution g, inert gas inlet h, stirrer i, reference electrode salt bridge j, clean mercury k, waste. [From Ref. 11, adapted with permission.]...

Figure 9.8 Experimental arrangement for use of thin-layer electrode constructed with glass or quartz plates. W, Working electrode R, reference electrode A, auxiliary electrode a, inert-gas inlet.

This would be accomplished by immersing the chemically modified electrode, a reference electrode, and an auxiliary electrode into an appropriate electrolyte solution (e.g., 0.1 M NaC104 in acetonitrile). The potential difference between the modified electrode (the working electrode) and the reference would then be adjusted to a value appropriate to drive this reaction, using a commercially available potentiostat, and the resulting anodic current would be measured. 

Figure 17.11 Transmission spectroelectrochemistry cell designed for use with room-temperature haloaluminate melts and other moisture-reactive, corrosive liquids, (a) Auxiliary electrode and reference electrode compartments, (b) quartz cuvette containing the RVC-OTE, (c) brass clamping screw, (d) passageway between the separator and OTE compartment, (e) fritted glass separator, (f) A1 plate, (g) lower cell body (Teflon), (h) upper cell body (Teflon). This cell is normally used inside a glove box and is optically accessed with fiber optic waveguides. [From E. H. Ward and C. L. Hussey, Anal. Chem. 59 213 (1987), with permission.]...

Figure 22.8 Schematic representation of an electrolysis cell (three-electrode construction W = working electrode AUX = auxiliary electrode R = reference electrode Q = coulometer D = diaphragm, if necessary CS = current source A = amperometer V = voltmeter).

For in vivo electrochemical measurement, the placement of the electrodes is important. In the potentiometric measurement (e.g., measurement of the pH of gastric juices) both the working electrode and the reference electrode are placed in the stomach. On the other hand, when amperometric measurement is done, the working electrode is in the place where you are getting the information from, but the auxiliary (reference) electrode can be anywhere, even on the skin. 

Broadly, the sensor contains, apart from the glassy-carbon working electrode, a reference electrode, a counter electrode, a temperature sensor and a pH glass electrode with associated reference electrode. As to the auxiliary sensor and electrodes, in the experiments on a laboratory scale, described in the previous chapters, types commonly used in research were employed. Here these need to be replaced by types which satisfy the above-mentioned requirements, which are discussed in the next section. 

Figure 5.26 Mercury-pool electrodes (a) cell with provision for pool replacement (b) plastic cup for pool (eu working electrode e2, auxiliary electrode e3, reference electrode).

Figure 1. Thin-layer electrochemical detector ( (A) auxiliary electrode (R) reference electrode (W) working electrode)...

FIGURE 8.17 Voltammetry scans on an ACC in 3mol L-1 KOH at various values of negative potential cutoff (-100mV stepwise shift). Auxiliary electrode nickel. Reference electrode Hg/HgO. (Adapted from Jurewicz, K., et al., Appl. Phys. A, 78, 981, 2004.)... 

Figure 7.4 shows an electrochemical cell containing a stationary planar working electrode, a reference electrode with Luggin capillary, and an auxiliary electrode. Some other types of more specialized cells are described in subsequent chapters. 

Fig. 8.3. Cell for the rotating ring-disc electrode. A, ring-disc electrode B, reference electrode with Luggin capillary C, auxiliary electrode D, Teflon lid E, porous frit F, thermostatted water jacket (adapted from Ref. 1 with...

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