Voltammetric measurement

Mercury electrodes (a) hanging mercury drop electrode (b) dropping mercury electrode (c) static mercury drop electrode. 

An electrode in which a drop of Hg is suspended from a capillary tube. 

An electrode in which successive drops of Hg form at the end of a capillary tube as a result of gravity, with each drop providing a fresh electrode surface. 

A metallic solution of mercury with another metal. 

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Scale of Operation Voltammetry is routinely used to analyze samples at the parts-per-million level and, in some cases, can be used to detect analytes at the parts-per-billion or parts-per-trillion level. Most analyses are carried out in conventional electrochemical cells using macro samples however, microcells are available that require as little as 50 pL of sample. Microelectrodes, with diameters as small as 2 pm, allow voltammetric measurements to be made on even smaller samples. For example, the concentration of glucose in 200-pm pond snail neurons has been successfully monitored using a 2-pm amperometric glucose electrode. ... 

Shipping analysis is an extremely sensitive electrochemical technique for measuring trace metals (19,20). Its remarkable sensitivity is attributed to the combination of an effective preconcentration step with advanced measurement procedures that generate an extremely favorable signal-to-background ratio. Since the metals are preconcentrated into the electrode by factors of 100 to 1000, detection limits are lowered by 2 to 3 orders of magnitude compared to solution-phase voltammetric measurements. Hence, four to six metals can be measured simultaneously in various matrices at concentration levels down to 10 10 i. utilizing relatively inexpensive... 

FIGURE 4-1 Schematic diagram of a cell for voltammetric measurements w.e., working electrode r.e., reference electrode c.e., counter electrode. The electrodes are inserted through holes in the cell cover. 

Practical examples of using preconcentrating CMEs include the use of a mixed 2,9-dimcthyl-1.10-phenanthrolinc/carbon-pastc electrode for trace measurements of copper (55), the use of clay-containing carbon pastes for voltammetric measurements of iron (56), the use of polyelectrolyte coatings for the uptake and... 

Thus in order to obtain the value of k it is absolutely necessary to know the standard cathodic redox potential. In the case of MeS02Ph, very fast voltammetric measurements at high sweep rates (1000 Vs 1) permit one to reach the reversible step of the sulphone and give °Meso2ph= — 1.85 V. Hence, the value k =0.9 x 105 s 1 may be estimated for the... 

Voltammetric measurements on defined soluble oligomers in the homologous series of the p-phenylenevinylenes and the p-phenylenes have finally ended specu-... 

Meylan S, Odzak N, Behra R, Sigg L (2004) Speciation of copper and zinc in natural freshwater comparison of voltammetric measurements, diffusive gradients in thin Aims (DGT) and chemical equilibrium models. An Chim Acta 510 91... 

Fan and Bard [140] employed capacitance and voltammetric measurements to investigate the photoelectrochemical behavior of n-WSe2, p-WSe2, and n-MoSe2 single-crystal electrodes in aqueous solutions containing various redox couples, namely Br /Br2, I /I, Fe(CN)6" /Fe(CN)6 , Fe /Fe, and... 

The most commonly used waveform for in vivo voltammetric measurements is square-wave. This involves the application of a potential pulse to the working electrode for a fixed time at fixed intervals. The current is measurai at the end of the potential pulse to minimize capacitive charging current contributions. This waveform is shown in Fig. 15 A. 

We have found new CO-tolerant catalysts by alloying Pt with a second, nonprecious, metal (Pt-Fe, Pt-Co, Pt-Ni, etc.) [Fujino, 1996 Watanabe et al., 1999 Igarashi et al., 2001]. In this section, we demonstrate the properties of these new alloy catalysts together with Pt-Ru alloy, based on voltammetric measurements, electrochemical quartz crystal microbalance (EQCM), electrochemical scanning tunneling microscopy (EC-STM), in situ Fourier transform infrared (FTIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). 

Figure 4 illustrates the dependence of on Aq for the case when r = 1 at several different values of [Fig. 4(a)] and when = 0.5 and at several different values of r [Fig. 4(b)]. From Fig. 4(a), one can see that takes a maximum around y = 0, i.e., Aq The volume ratio affects strongly the value of as shown in Fig. 4(b), which is ascribed to the dependence of the equilibrium concentration on r through Eq. (25). This simple example illustrates the necessity of taking into account the variation of the phase-boundary potential, and hence the adsorption of i, when one tries to measure the adsorption properties of a certain ionic species in the oil-water two-phase systems by changing the concentration of i in one of the phases. A similar situation exists also in voltammetric measurements of the transfer of surface-active ions across the polarized O/W interface. In this case, the time-varying thickness of the diffusion layers plays the role of the fixed volume in the above partition example. The adsorption of surface-active ions is hence expected to reach a maximum around the half-wave potential of the ion transfer. 

In the second category, SECMIT has been used to probe the relative permeability of oxygen between water and DCE or NB, with no supporting electrolyte present in any phase. Under the conditions employed, direct voltammetric measurements in the organic phase would be impractical due to the high solution resistivity (DCE or NB) or limitations of the solvent window available (NB). Figure 24 shows the steady-state current for the... 

In this chapter our focus is on principles, theory, and applications of micro-ITIES to quantitative voltammetric measurements of CT processes and ionic reactions in solution. The questions of characterization of the interfacial geometry and surrounding insulator, which are essential for both kinetic measurements and analytical applications of micro-ITIES, will also be discussed. 

The theory has been verified by voltammetric measurements using different hole diameters and by electrochemical simulations [13,15]. The plot of the half-wave potential versus log[(4d/7rr)-I-1] yielded a straight line with a slope of 60 mV (Fig. 3), but the experimental points deviated from the theory for small radii. Equations (3) to (5) show that the half-wave potential depends on the hole radius, the film thickness, the interface position within the hole, and the diffusion coefficient values. When d is rather large or the diffusion coefficient in the organic phase is very low, steady-state diffusion in the organic phase cannot be achieved because of the linear diffusion field within the microcylinder [Fig. 2(c)]. Although no analytical solution has been reported for non-steady-state IT across the microhole, the simulations reported in Ref. 13 showed that the diffusion field is asymmetrical, and concentration profiles are similar to those in micropipettes (see... 

The use of micropipette electrodes for quantitative voltammetric measurements of ion transfer (IT) and electron transfer (ET) reactions at the ITIES requires knowledge of geometry of the liquid interface. For the micrometer-sized micropipettes, both the orifice radius and the thickness of the pipette wall can be measured microscopically. A typical error of the microscopic determination of a radius was estimated to be 0.5/am for a micropipette and 1 /am for a microhole [24]. 

The electrochemical cell for the polarographic measurements had a four-electrode configuration equipped with a microsyringe, and was connected to a computer-assisted data-acquisition system [7]. On the other hand, the cyclic voltammetric measurements that are also assisted by a computer data-acquisition system were carried out using a gel electrode that contains the aqueous phase [8]. The cell structure was as follows ... 

KKma J, Bernard C, Degrand C (1994) Sonoelectrochemistry effects of ultrasound on voltammetric measurements at a solid electrode. J Electroanal Chem 367 297-300... 

In this connection, cyclic voltammetric measurements on the electrochemical reduction of C02 at n-Ti02 and platinized Ti02 film electrodes were reported a little later by Augustynski and co-workers.87 The existence of two electrochemically detectable species resulting from C02 reduction was suggested by anodic peaks on the cyclic voltammograms (Fig. 4). Unfortunately, however, no... 

Wangfuengkanagul and Chailapakul [9] described the electroanalysis of ( -penicillamine at a boron-doped diamond thin film (BDD) electrode using cyclic voltammetry. The BDD electrode exhibited a well-resolved and irreversible oxidation voltammogram, and provided a linear dynamic range from 0.5 to 10 mM with a detection limit of 25 pM in voltammetric measurement. In addition, penicillamine has been studied by hydrodynamic voltammetry and flow injection analysis with amperometric detection using the BDD electrode. 

Nelson [8] studied voltammetric measurement of copper (Il)-organic interactions in estuarine waters. Based on results of previous studies on the effects of organic matter on adsorption of copper at mercury surfaces, Nelson developed a method to evaluate the interactions between divalent copper and... 

We have recently performed a variety of these and related SPAIRS-voltammetric measurements on platinum and palladium <5c. 12b ), and have concluded that the adsorbed CO formed in most cases acts predominantly as a poison for organic electrooxidation. Interestingly, the potential at which the CO undergoes electrooxidation, and hence where the electrocatalysis commences, can be strongly dependent on the structure of the solution species involved. Thus for acetaldehyde, for example, this process occurs at about 0.3 V lower overpotentials than for benzaldehyde under comparable conditions (5c). 

The electrosynthesis of metalloporphyrins which contain a metal-carbon a-bond is reviewed in this paper. The electron transfer mechanisms of a-bonded rhodium, cobalt, germanium, and silicon porphyrin complexes were also determined on the basis of voltammetric measurements and controlled-potential electrooxidation/reduction. The four described electrochemical systems demonstrate the versatility and selectivity of electrochemical methods for the synthesis and characterization of metal-carbon o-bonded metalloporphyrins. The reactions between rhodium and cobalt metalloporphyrins and the commonly used CH2CI2 is also discussed. 

In the absence of other substrates which are easily reduced, halosilanes can be reduced by cathodic reaction. However, it is rather difficult to determine the reduction potentials of halosilanes, because halosilanes are readily hydrolyzed during voltammetric measurements. Although early reports stated that the reduction potential of Me3SiCl is not very negative, extensive studies by Corriu... 

The standard potentials of practically all oxidation and reduction reactions, especially those common in the environment and soil, are known or can easily be determined. Because of the specificity and relative ease of conducting voltammetric measurements, they might seem well suited to soil analysis. There is only one major flaw in the determination of soil constituents by voltammetric analysis and that is that in any soil or soil extract, there is a vast array of different oxidation-reduction reactions possible, and separating them is difficult. Also, it is not possible to start an investigation with the assumption or knowledge that all of the species of interest will be either oxidized or reduced. 

Without any doubt, cyclic voltammetry is the most popular voltam-metric technique used in the field of inorganic chemistry. Unfortunately, the power of the technique is frequently overestimated in that simple cyclic voltammetric measurements rarely allow one to gain complete electrochemical information. As we will discuss, it must be always coupled with complementary techniques. 

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