Electrodes functionalized

Membrane Potentials Ion-selective electrodes, such as the glass pH electrode, function by using a membrane that reacts selectively with a single ion. figure 11.10 shows a generic diagram for a potentiometric electrochemical cell equipped with an ion-selective electrode. The shorthand notation for this cell is... 

The most important rechargeable lithium batteries are those using a soHd positive electrode within which the lithium ion is capable of intercalating. These intercalation, or insertion, electrodes function by allowing the interstitial introduction of the LE ion into a host lattice (16,17). The general reaction can be represented by the equation ... 

The main chemico-analytical properties of the designed ionoselective electrodes have been determined. The work pH range of the electrodes is 1 to 5. The steepness of the electrode function is close to the idealized one calculated for two-charged ions (26-29 mV/pC). The electrode function have been established in the concentration range from 0.1 to 0.00001 mole/1. The principal advantage of such electrodes is the fact that thiocyanate ions are simultaneously both complexing ligands and the ionic power. The sensitivity (the discovery limits), selectivity (coefficient of selectivity) and the influence of the main temporal factors (drift of a potential, time of the response, lifetime of the membranes) were determined for these electrodes. 

In such reactions, even though the indicator electrode functions reversibly, the maximum value of AE/AV will not occur exactly at the stoichiometric equivalence point. The resulting titration error (difference between end point and equivalence point) can be calculated or can be determined by experiment and a correction applied. The titration error is small when the potential change at the equivalence point is large. With most of the reactions used in potentiometric analysis, the titration error is usually small enough to be neglected. It is assumed that sufficient time is allowed for the electrodes to reach equilibrium before a reading is recorded. 

As indicator electrodes glass and antimony electrodes are commonly used, but it must be noted that in benzene-methanol solutions, a glass-antimony electrode pair may be used in which the glass electrode functions as reference electrode. Glass electrodes should not be maintained in non-aqueous solvents for long periods, as the hydration layer of the glass bulb may be impaired and the electrode will then cease to function satisfactorily. 

Note that a number of complicating factors have been left out for clarity For instance, in the EMF equation, activities instead of concentrations should be used. Activities are related to concentrations by a multiplicative activity coefficient that itself is sensitive to the concentrations of all ions in the solution. The reference electrode necessary to close the circuit also generates a (diffusion) potential that is a complex function of activities and ion mobilities. Furthermore, the slope S of the electrode function is an experimentally determined parameter subject to error. The essential point, though, is that the DVM-clipped voltages appear in the exponent and that cheap equipment extracts a heavy price in terms of accuracy and precision (viz. quantization noise such an instrument typically displays the result in a 1 mV, 0.1 mV, 0.01 mV, or 0.001 mV format a two-decimal instrument clips a 345.678. .. mV result to 345.67 mV, that is it does not round up ... 78 to ... 8 ). 

Another version of cell or group arrangement is that using bipolar electrodes (Eig. 18.1a). Here, combined electrodes are used One side of the electrode functions... 

The insertion is monopolar when the electrode functions exclusively as either the anode or the cathode and in this case it is connected with one of the poles of the electric source as shown in Figure 6.22 (a-f). Since the voltage for a single cell is very small (of the order of one to a few volts) several cells are usually connected in series and parallel combinations such that the overall potential drop corresponds to the available direct current power source. With bipolar insertions, however, there are a number of electrodes in each cell which function as anodes on one side and as cathodes on the other apart from the end electrodes, these are not directly connected to the electric source. 

In the tables we find i Ag+/Ag = 0.7996 V and 2 Agci/Ag = 0.2223 V. From the above it is clear that primarily the silver-silver chloride electrode functions as a pAg electrode, i.e., it measures oAg+ at an ionic strength above 0.01 (cf., extended Debye-Hiickel expressions) the calculation of [Ag+ ] becomes more difficult, and even more so for [Cl ], where the solubility product value is also involved. 

Neither the usual membrane ISEs nor the gas-sensing electrodes, in which their internal indicator electrode functions as a zero-current potentiometric half-cell, are under consideration here. 

One may think that the idea of detecting ionic compounds such as heparin using polymeric ion-selective electrodes seems very difficult due to the high charge of polyionic molecules, which makes the slope of the electrode function negligibly small for an analytical application. Indeed, for heparin-selective electrodes the theoretical slope is less than lmV decade 1 and the potential practically does not depend on heparin concentration, which means that this ISE can be useful as a reference electrode [33], Nonetheless, Ma and Meyerhoff noticed that the potential of polymeric membrane... 

The ellipsometer used in this study is described elsewhere(3). It consists of a Xenon light source, a monochromator, a polarizer, a sample holder, a rotating analyzer and a photomultiplier detector (Figure 1). An electrochemical cell with two windows is mounted at the center. The windows, being 120° apart, provide a 60° angle of incidence for the ellipsometer. A copper substrate and a platinum electrode function as anode and cathode respectively. Both are connected to a DC power supply. The system is automated with a personal computer to collect all experimental data during the deposition. Data analysis is carried out by a Fortran program run on a personal computer. 

Polymers have served roles in PEM fuel cell cathodes such as modifiers to macrocycle-based electrodes to improve conductivity and stability,165 composite materials with heteropolyacids,166 and as precursors to pyrolyzed catalysts.38,112,132,133 However, as discussed in the previous section, the activity of nitrogen-containing carbon raises the possibility of non-metal electrodes functioning in a cathode environment. Likewise, researchers have noted ORR activity for various conducting polymers containing nitrogen, and recently studies on their potential use in PEM fuel cell cathodes have been reported. 

Fouling of the reference electrode or the reference side of a combination electrode is a common problem in soil pH measurements. Fouling can be caused by salts, organic matter, and clay. Each electrode manufacturer will provide specific cleaning procedures that help to keep electrodes functioning properly however, in many cases, no amount of cleaning is effective and the electrodes need to be replaced. 

We then described how ion-selective electrodes (ISEs) function by means of generating an emf that is related to the activity of a single ion. The simplest ISEs are glass electrodes for pH determination, and the related pH combination electrodes. Other solid-state ISEs, such as the fluoride electrode, function in the same way. 

In the electrode with CuS alone, which has negligible conductivity, the precipitate ISE with a silicone rubber matrix has better properties than the electrode with a pressed pellet [314], The ISE with a mixture of CuS and Agi S finds broad application [325]. If the membrane is prepared by pressing, the grains of these two compounds combine to form jalpaite, Agi.55C%.4sS [180], This substance is a mixed conductor with transport numbers of Ag, 0.69 Cu(I), 0.30 and electrons, 0.01, at 25 C [175]. The sintered electrode also contains Ag1.2Cuo.8S or Ago.93Cu1.07S. Oxidation of these phases leads to considerable deterioration in the electrode function [180]. Good electrodes... 

In this section, we present material dealing with the direct oxidation and reduction of a variety of organocobalt species, including complexes with more than one cobalt center, electrodes functionalized with cobalt complexes, cobalt-containing SchifF-base complexes, cobalt porphyrins and corroles, and macrocyclic tetraamines. 

A useful variation of the amperometric titration involves measuring the current resulting from a small fixed potential applied across two working electrodes. One electrode functions as an anode and the other as a cathode. Once again, the expected current behavior during a titration can be explained by means of hydrodynamic voltammograms. Position a in Figure 3.43A shows the small po-... 

The E (I"oxtin>) values are data from the literature (22) and our own measurements, and the E°(FeCp2+/°)surf. are from the cyclic voltammetry peak positions for Pt electrodes functionalized with I in the various solvents. Together, these data provide information concerning the driving force for the oxidation of I- by (FeCp2+)surf. in the various solvents. 

The electrochemistry of cytochrome c is attracting much attention,690 in particular the development of electrodes for cytochrome c, which either have a redox mediator bound to the surface, or utilize a solution mediator. Examples are a platinum gauze electrode functionalized with 2,3,4,5-tetramethyl-l-(dichlorosilyl)methyl[2]ferrocenophane,691 and 4,4 -bipyridyl, which serves as a bridge between cytochrome c and the electrode.692... 

Two EPMEs based on maltodextrins with different value of DE (maltodextrin I DE 4.0-7.0 maltodextrin II DE 16.5-19.5) were proposed for the assay of baclofen enantiomers in baclofen raw materials and from its pharmaceutical formulation, Norton-Baclofen tablets [37]. The slopes of the electrode function of the proposed electrodes were 55.0mV/pS-baclofen for maltodextrin I-based electrode and 59.0 mV/pR-baclofen for maltodextrin II-based electrode and the detection limits were 1.34 x 10 6mol/L (S-baclofen) and 2.52 x 10 10 mol/L (R-baclofen), respectively. 

An EPME based on vancomycin was proposed for the assay of D-pipecolic acid [50]. The linear concentration range for the proposed enantioselective membrane electrode is 10 9-10 6mol/L with the slope of electrode function 60.2 mV/p(D-pipecolic acid). The enantioselectivity was determined over L-pipecolic acid. The proposed electrode could be reliably employed for the assay of D-pipecolic acid in serum samples. 

The observation of luminescence from laser dyes by ECL methods offers the possibility of using this approach to create dye lasers. A laser operating by ECL would not require an additional pump laser, and enhanced power, tunability, and wavelength selection are additional factors. While the pumping rate achieved by ECL previously has been two orders of magnitude lower than the optimal, Horiuchi et al. have reported a device structure designed to enhance the ECL efficiency and realize laser action driven by ECL [67], This experiment is illustrated in Fig. 14. A pair of sputter-deposited platinum film electrodes were positioned facing each other 2 to 7 microns apart. One electrode functioned... 

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