Potentiostatic configuration

This potentiostat configuration is universal in that it can operate with any type function from the function generator (e.g., ramp, square wave, sine wave). 

The alternating current measurements over the frequency interval [8 X 10 , 2 X 10 ] Hz were performed using a Solartron mod. 1286 electrochemical interface and a Solartron mod. 1250 analyzer, controlled by the SOFTCOR-AC-PIC program [69], adopting the potentiostatic configuration and applying a sinusoidal voltage of 5 mV RMS amplitude. 

The bcLsic component of electrochemical instrumentation is the potentiostat. The use of a single computer or microprocessor to control voltammetric instrumentation is well established and many digitally controlled potentiostat configurations have been described/ but the limited capabilities of microprocessors may render their use difficult and a minicomputer system is quite expensive for control purposes. On the other hand, the use of two computers, a microprocessor or a microcomputer for realtime control of the experiment and a host computer for data evaluation, offers several advantages. In addition, the large multi-user minicomputer can be replaced by a personal computer to give the operator full control over the system. ... 

The solution to reference electrode instabiUty is the introduction of a third or auxiUary electrode. This particular electrode is intended to carry whatever current is required to keep the potential difference between the working and reference electrodes at a specified value, and virtually all potentiostats (instmments designed specifically for electrochemistry) have this three-electrode configuration. Its use is illustrated in Figure 3. 

FIGURE 6-20 Configuration of a penicillin sensor based on an microarray electrode coated with a pH-responsive polypyrrole. Vq = gate voltage VD = drain voltage ID = drain current PS = potentiostat CE and RE = counter and reference electrodes, respectively. (Reproduced with permission from reference 76.)... 

The CCD detector and the potentiostat were synchronized in an open-loop configuration by starting the experiment with a common trigger. Careful measurements... 

Using the unique four-electrode STM described above, Bard and coworkers (Lev, 0. Fan, F-R.F. Bard, A.J. J. Electroanal. Chem.. submitted) have obtained the first images of electrode surfaces under potentiostatic control. The current-bias relationships obtained for reduced and anodically passivated nickel surfaces revealed that the exponential current-distance relationship expected for a tunneling-dominated current was not observed at the oxide-covered surfaces. On this basis, the authors concluded that the nickel oxide layer was electrically insulating, and was greater than ca. 10 A in thickness. Because accurate potential control of the substrate surface is difficult in a conventional, two-electrode STM configuration, the ability to decouple the tip-substrate bias from... 

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.

Fig. 7.186. Reactor cell (a) and electrode configuration (b) for NEMCA studies using the fuel-cell type design, G-P, gal-vanostat-potentiostat. (Reprinted with permission from C. G. Vayenas, S. Bebelis, I. V. Yentekakis and H. Glintz, Catalysis Today 11 303,1992.)...

An alternative way of measurement is to incorporate the cell in a bridge circuit as shown in Fig. 16. The configuration of the bridge is identical to the classical Wien bridge [49] except that the a.c. voltage is supplied via the potentiostat so that, simultaneously, the mean d.c. potential E can be controlled as usual [21, 22]. The adjustable series combination of the resistor Rs and the capacitor Cs offers an impedance Zs, given by... 

M. Souto, Electronic Configurations in Potentiostats for the Correction of Ohmic Losses, Electroanalysis 6 531-542 (1994). 

Instrumentation for selected aspects of electroanalytical chemistry is covered in Chapters 6-8. Although computers have made a tremendous impact on electroanalytical instrumentation, many aspects of these chapters are timeless. The basic configurations of a potentiostat have not changed since the early 1960s, although the electronic components themselves are dramatically different Learn to build your own potentiostat in Chapter 6, then see how to fine-tune it in Chapter 7. 

The instrumentation consisted of the hand-held potentiostat interfaced with a CH8 multiplexer (PalmSens) (Fig. 29.3) that allow different sensor configuration ... 

Actually, there are reports on transforming the negative effect of separation electric field into new detection approaches. A potentiostat-less detection scheme for amperometric detection in CE based on the use of microband array electrodes situated in the CE electric field has been proposed [53] as well as the use of an indirect amperometric detection with a carbon fibre in-channel configuration [54]. In this case, the potential difference induced by the CE separation electric field produces a change in the reduction potential of oxygen, which can be used to determine nonelectroactive analytes. 

Ohmic drop in three-electrode circuits. In modem coulometry and voltammetry the use of a potentiostat and a three-electrode configuration is the routine practice. The three electrodes are usually called the working, reference, and counter (or auxiliary) electrodes (see Figure 5.2). The cell current passes between the working electrode immersed in the test solution and the counter electrode, which may be in the test solution but is usually isolated from it by a single- or double-junction glass frit. 

Fig. 17 shows how such an ideal op amp can be configured as a potentiostat and connected to an electrochemical cell to study kinetics. First consider the electrochemical cell in the schematic. Unlike the cells discussed above, this cell has three electrodes. The working elecrode (WE) represents the interface of inter-... 

Figure 17 Configuration of op amp to function as a potentiostat. The desired Vin is set by the experimenter via the voltage divider on the left, which consists of a battery and a variable resistor. The path of the current is shown, indicating that no current passes through the RE.

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