Supporting electrolytes, voltammetry

In stripping voltammetry the stripping potential of a given ion is generally close to the polarographic half-wave potential of that ion in solutions with similar supporting electrolytes. Thus, typical stripping potentials in a 0.05M potassium chloride base solution are as follows Zn, — 1.00 V Cd, -0.07 V Pb, -0.45 V Bi, -0.10 V Cu(II), -0.05 V. 

Sodium-silicate glass, 151 Sol-gel films, 120, 173 Solid electrodes, 110 Solid state devices, 160 Solvents, 102 Speciation, 84 Spectroelectrochenristry, 40 Spherical electrode, 6, 8, 9, 61 Square-wave voltammetry, 72, 92 Staircase voltammetry, 74 Standard potential, 3 Standard rate constant, 12, 18 Stripping analysis, 75, 79, 110 Supporting electrolyte, 102 Surface-active agents, 79... 

The concentration of the transferred ion in organic solution inside the pore can become much higher than its concentration in the bulk aqueous phase [15]. (This is likely to happen if r <5c d.) In this case, the transferred ion may react with an oppositely charged ion from the supporting electrolyte to form a precipitate that can plug the microhole. This may be one of the reasons why steady-state measurements at the microhole-supported ITIES are typically not very accurate and reproducible [16]. Another problem with microhole voltammetry is that the exact location of the interface within the hole is unknown. The uncertainty of and 4, values affects the reliability of the evaluation of the formal transfer potential from Eq. (5). The latter value is essential for the quantitative analysis of IT kinetics [17]. Because of the above problems no quantitative kinetic measurements employing microhole ITIES have been reported to date and the theory for kinetically controlled CT reactions has yet to be developed. 

The voltammograms at the microhole-supported ITIES were analyzed using the Tomes criterion [34], which predicts ii3/4 — iii/4l = 56.4/n mV (where n is the number of electrons transferred and E- i and 1/4 refer to the three-quarter and one-quarter potentials, respectively) for a reversible ET reaction. An attempt was made to use the deviations from the reversible behavior to estimate kinetic parameters using the method previously developed for UMEs [21,27]. However, the shape of measured voltammograms was imperfect, and the slope of the semilogarithmic plot observed was much lower than expected from the theory. It was concluded that voltammetry at micro-ITIES is not suitable for ET kinetic measurements because of insufficient accuracy and repeatability [16]. Those experiments may have been affected by reactions involving the supporting electrolytes, ion transfers, and interfacial precipitation. It is also possible that the data was at variance with the Butler-Volmer model because the overall reaction rate was only weakly potential-dependent [35] and/or limited by the precursor complex formation at the interface [33b]. 

The facilitated ion transfers of some alkaline earth metals have been also studied in the DCE systems by the cyclic voltammetry. These systems perhaps have not been studied by any solvent extraction methods yet. Typical voltammograms in the N15C5 diffusion-control systems are shown in Fig. 6. The aqueous supporting electrolyte was MgCl2 instead of MgS04 in these measurements because BaS04 precipitated. 

Before mentioning some more literature data on non-aqueous voltammetry, we suggest on the basis of our previous discussions that the choice of the experimental conditions used in the techniques must be a compromise between a sufficient solubility of the analyte in the solution, an ample redox potential range of the solvent, a suitable type of indicator electrode and adequate conductance of the solution with supporting electrolyte added. In this connection Fig. 4.20 may be a useful guide. 

The reversibility of the carrier was tested by cyclic voltammetry. The scan of the solvent and supporting electrolyte is shown in Fig. 13, with and without dissolved oxygen. The oxygen reduction occurs at about — 0.43 V. (vs. SCE). The scan with the complex added, but the solution free of dissolved oxygen is shown as Fig. 14. The carrier is seen to be reduced at about 0.04 V, well within the window of the solvent and electrolyte, and well before reduction of molecular oxygen. 

The electrochemical behavior of niclosamide was described on the basis of d.c. polarography, cyclic voltammetry, a.c. polarography, and differential pulse polar-ography, in the supported electrolytes of pH ranging from 2.0 to 12.0 [32], A tentative mechanism for the reduction of niclosamide is proposed that involves the transfer of 4 e . Parameters such as diffusion coefficients and heterogeneous forward rate constant values were evaluated. 

Chemical reactivity of unfunctionalized organosilicon compounds, the tetraalkylsilanes, are generally very low. There has been virtually no method for the selective transformation of unfunctionalized tetraalkylsilanes into other compounds under mild conditions. The electrochemical reactivity of tetraalkylsilanes is also very low. Kochi et al. have reported the oxidation potentials of tetraalkyl group-14-metal compounds determined by cyclic voltammetry [2]. The oxidation potential (Ep) increases in the order of Pb < Sn < Ge < Si as shown in Table 1. The order of the oxidation potential is the same as that of the ionization potentials and the steric effect of the alkyl group is very small. Therefore, the electron transfer is suggested as proceeding by an outer-sphere process. However, it seems to be difficult to oxidize tetraalkylsilanes electro-chemically in a practical sense because the oxidation potentials are outside the electrochemical windows of the usual supporting electrolyte/solvent systems (>2.5 V). 

Obtained by both cyclic (100 mV s-1) and square-wave (10 Hz, Osteryoung-type) voltammetry in acetonitrile solution containing 0.1 mol dm-3 BuJNBF4 as supporting electrolyte. Solutions were 1 x 10-3 mol dm-3 in compound with reference to an Ag/Ag+ electrode (330 10 mV vs SCE) at 21 1°G b Anodic shift of the reduction waves of [57] in the presence of 1.0 equiv of the respective cationic species added as their perchlorate or hexafluorophosphate salts. "Anodic shift in the presence of 2.0 equiv of the respective cations. The second reduction wave of [57] became obscure or disappeared in the presence of more than 1 equiv of the respective cations. 

Cyclic voltammetry was conducted using a Powerlab ADI Potentiostat interfaced to a computer. A typical three electrode system was used for the analysis Ag/AgCl electrode (2.0 mm) as reference electrode Pt disc (2.0 mm) as working electrode and Pt rod (2.0 mm) as auxiliary electrode. The supporting electrolyte used was a TBAHP/acetonitrile electrolyte-solvent system. The instrument was preset using a Metrohm 693 VA Processor. Potential sweep rate was 200 mV/s using a scan range of-1,800 to 1,800 mV. 

UMEs decrease the effects of non-Earadaic currents and of the iR drop. At usual timescales, diffusional transport becomes stationary after short settling times, and the enhanced mass transport leads to a decrease of reaction effects. On the other hand, in voltammetry very high scan rates (i up to 10 Vs ) become accessible, which is important for the study of very fast chemical steps. For organic reactions, minimization of the iR drop is of practical value and highly nonpolar solvents (e.g. benzene or hexane [8]) have been used with low or vanishing concentrations of supporting electrolyte. In scanning electrochemical microscopy (SECM [70]), the small size of UMEs is exploited to locahze electrode processes in the gm scale. 

Fig. 3.10 Square-wave voltammetry of adriamycin adsorbed on mercury electrode. A net response and its forward and backward components. The concentration of adriamycin is 1.72 x 10 " M and the supporting electrolyte is 0.9 M KNO3, pH 4.65. Adriamycin is accumulated during 30 s from unstirred solution, at —0.1 V. sw = 50 mV, / = 10 Hz and AE = —2 mV (reprinted from [190] with permission)...

Song et al. have reported the determination of chlorpromazine by adsorptive stripping voltammetry [169]. Phosphate buffer saline solution (pH 7.4), consisting of 0.2 g KH2PO4,1.15 g Na2HP04,0.2 g KCl, 8 g NaCl, and 0.047 g MgCl2, was used as the supporting electrolyte. Two methods were reported for the determination of chlorpromazine ... 

The ferrocenyl dendrimers were electrodeposited in their oxidized forms onto the electrode surfaces (platinum, glassy-caibon, and gold) either by controlled potential electrolysis or by repeated cycling between the appropriate anodic and cathodic potential limits therefore the amount of electroactive material electrode-posited can be controlled with the electrolysis time or the number of scans. The electrochemical behavior of films of the polyfeirocenyl dendrimers was studied by cyclic voltammetry in fresh CH2CI2 and CHjCN solutions containing only supporting electrolyte. 

In this solvent, using CV and Osteryoung square-wave voltammetry (OSWV) under high vacuum conditions at room temperature, Cgo displays a one-electron, chemically reversible oxidation wave at +1.26 V vs. Fc/Fc+. TBAPFe was used as the supporting electrolyte. Under the same conditions, the first one-electron oxidation of C70 occurs at +1.20 V, 60 mV more negative (easier to oxidize) than that of Cgo- Both oxidations are electrochemically quasireversible with A pp = 80 mV. In addition, a second oxidation wave is observed for C70 close to the limit of the solvent potential window at+1.75 V. However, this wave appears to be chemically irreversible (see Fig. 3) [36]. 

Fig. 1 Cyclic voltammetry pattern at a glassy carbon electrode (GC Tokai, Japan) with 10 M a-K6P2Wig062 in 1 M HCl supporting electrolyte. Sweep rate 100 mV s electrode surface area ...

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