Electrochemical, detection window

In the last step of an assay, i.e. during the electrochemical detection of the electroactive species of interest, a new window appears in order to let the experimenter follow the detection on-line. As presented in Fig. 36.8, the software has been designed to perform chrono-amperometric measurements of the desired analyte. On the left part of the window the raw measurement data that provide the evolution of the current for each microchannel that is measured during a time period of generally 2 s appears. With the multi-potentiostat used, the eight channels are... 

Figure 36.8. Example of Immusoft window appearing during the electrochemical detection step of an assay. On the left-hand side, the figure shows the row amperometric data, from which the deduced faradaic current is automatically displayed for each microchannel in the current versus time plot shown on the left-hand side of the window.

The inertness of the surface raises interesting questions. The aqueous solvent window is pushed out as a result of water electrolysis being an inner-sphere mechanism. As a result, it is often stated in the literature that BDD can detect species which other electrodes cannot due to the extended solvent window. This is certainly true of outer-sphere species, but care must be taken when considering inner-sphere species. Heterogeneous ET will be retarded for many of these species on BDD, as there are no favorable adsorption sites, pushing out their electrochemical detection potential. Therefore, each species should be considered on a case-by-case basis, in combination with the effect of surface termination. For example, both oxidation [89] and reduction, in... 

In addition, ECL experiments can also be carried out using a commercial fluorescence spectrometer coupled with an electrochemical instrument with the excitation function of the fluorimeter disabled. For example, one can have the three electrodes fitted into a standard fluorescence cuvette so that the entire cell system fits into the sample compartment of the spectrometer. The electrodes should be arranged so that the working electrode faces the detection window of the emission monochromator. ECL intensity can be measured either at... 

BDD MDA electrodes are useful for electrochemical detection of various biologically and environmentally important chemical species with high sensitivity and stability. Sigmoidal voltammograms could be obtained for (A) ascorbic acid and (B) 3,4-dihydroxyphenylacetic acid (DOPAC), as shown in Fig. 11.3. Steady-state current was observed even at potentials as high as +1.2 V vs Ag/AgCl, due to the wide potential window of BDD. 

Diamond is unique for the detection of carbamate pesticides as well as their phenolic derivatives to achieve high sensitivity and long-term stability [40]. While the wide electrochemical potential window is advantageous for the direct detection of carbamate pesticides at high oxidation potential, the low adsorption behavior of diamond improves the stability of the hydrolyzed phenolic derivatives of these pesticides. The phenolic... 

Conductive boron-doped diamond is gaining popularity as a unique electrode material for electroanalytical applications. While its wide electrochemical potential window allows the detection of compounds oxidizing at high potentials, its resistance to the adsorption of chemical species on its surface allows the stable electrochemical detection of a number of different chemical species. Electrochemical pre-treatment of the electrode surface to convert... 

One of the most difficult tasks of the IR spectro-electrochemist is to differentiate between the information that comes from the adsorbed molecules and that which comes from molecules in solution. If one compares the amount of molecules that are in the bulk of a solution (e.g., —10 in 10 cm of a 10 mol dm solution) with those adsorbed on the surface of the electrode (—1015), it is easy to understand why The IR absorbance from the electrolyte solution would be so much stronger (in our example 10,000 times stronger) than that from adsorbed molecules, that it would not be possible to detect the latter. To increase the sensitivity of the absorbance of the adsorbed molecules, the design of the electrochemical vessel is very important. Generally, the electrode is placed very close to the window through which the IR beam enters and then is reflected (Fig. 6.22). In this configuration, the amount of electrolyte solution... 

The vertical axis is in volts relative to the saturated calomel reference electrode (SCE). Photoemission in aqueous media is best performed in the electrochemical window, between the hydrogen and oxygen evolution redox potentials, where small dc currents allow easier detection of the photoemission current. Protons are used for scavenging the... 

The standard tools such as FTIR, NMR, MS and UV-Vis are not sufficient for the requirements of nonaqueous electrochemistry, that is, detection of impurities in the solvents at a ppm level. The best of these methods, the NMR, can detect impurities only at a subpromil level, which is too high. As discussed in the chapter dealing with the electrochemical windows of nonaqueous systems, a few tens of ppm of contaminants can considerably affect the electrochemical behavior. Therefore, GC or HPLC are the only appropriate methods available today [3-5], However, it is important to note that there are solvents that can partially decompose in the injection port or in the column of the GC. The relevant solvents are those whose normal boiling points are high, and thus their GC analysis requires high temperatures. For example, PC, EC, BL and SL are typically problematic for GC analysis. 

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