Supporting Electrolyte concentration

FIG. 9 Simulated electrical potential and space charge density profiles at the water-1,2-DCE interface polarized at/= 5 in the absence (a) and in the presence (b) of zwitterionic phospholipids. The supporting electrolyte concentrations are c° = 20 mM and c = 1000 mM. The molecular area of the phospholipids is 150 A, and the corresponding surface charge density is a = 10.7 xC/cm. The distance between the planes of charge associated with the headgroups is d = 3 A. 

FIG. 10 Simulated enhancement factor for monolayers of zwitterionic phospholipids with different molecular areas (shown on the curves) at the polarized water-1,2-DCE interface. The supporting electrolyte concentrations are c° = 20 mM and c" = 1000 mM. 

Redox couple Supporting electrolyte Concentration of redox couple (oxid red) D0 x 106 (cm2/s) a (meas.) k°a (cm/s) Zero-point method ... 

Hetero-excimer chemiluminescence yields were measured by A. Weller and K. Zachariasse 214) the system dimethylanthracene anion radical/tri-p-tolylaminium perchlorate in tetrahydrofurane exhibits particularly strong chemiluminescence with quantum yields of about 7.5 x 10-2 215>. A. J. Bard and coworkers 216> very thoroughly investigated the influence of several parameters, e.g. supporting electrolyte concentration, on the efficiency of electrogenerated chemiluminescence. 

As indicated above, all of the experimental data reported thus far were obtained at low concentrations of both supporting electrolyte (mM) and electroactive species (pM). This was done because we have observed an interesting effect of supporting electrolyte concentration on the shape of the voltammetric waves observed at the NEEs [25]. We have found that the reversibility of the voltammetric waves for all couples investigated to... 

EIG. 10. Cyclic voltammograms illustrating the effect of supporting electrolyte concentration at a lONEE. 5 pM TMAFc in aqueous NaNOs at the indicated concentrations of NaNOs. Scan rate = 100 mV s h... 

Examination of the behaviour of a dilute solution of the substrate at a small electrode is a preliminary step towards electrochemical transformation of an organic compound. The electrode potential is swept in a linear fashion and the current recorded. This experiment shows the potential range where the substrate is electroactive and information about the mechanism of the electrochemical process can be deduced from the shape of the voltammetric response curve [44]. Substrate concentrations of the order of 10 molar are used with electrodes of area 0.2 cm or less and a supporting electrolyte concentration around 0.1 molar. As the electrode potential is swept through the electroactive region, a current response of the order of microamperes is seen. The response rises and eventually reaches a maximum value. At such low substrate concentration, the rate of the surface electron transfer process eventually becomes limited by the rate of diffusion of substrate towards the electrode. The counter electrode is placed in the same reaction vessel. At these low concentrations, products formed at the counter electrode do not interfere with the working electrode process. The potential of the working electrode is controlled relative to a reference electrode. For most work, even in aprotic solvents, the reference electrode is the aqueous saturated calomel electrode. Quoted reaction potentials then include the liquid junction potential. A reference electrode, which uses the same solvent as the main electrochemical cell, is used when mechanistic conclusions are to be drawn from the experimental results. 

Fig. 9 Pressure and supporting electrolyte concentration dependences of rate constants feel for the CoWi2O40 electrode reaction in aqueous KCl at 25.0 C, [KCI] = 0.10 ( ), 0.20 ( ), 0.50 (A), and 1.00 (T ) mol L h hollow symbols represent return to low pressure after the pressure cycle. [K6C0W12O40] = 1.0 mmol L (taken from Ref 60).

The double-layer influence on the electrode reaction of Zn(II)/Zn(Hg) on DME in NaNOs solutions was studied in the concentration range from 0.01 to 1 M, using dc and ac polarography [30]. The apparent rate constants of the Zn(II)/Zn(Hg) system increase with dilution of the NaN03 supporting electrolyte. However, after the Frumkin correction, the rate constant was virtually independent of the supporting electrolyte concentration. 

The adsorbability of monovalent and divalent ions on either the sodium or calcium form of montmorillonite decreases with supporting electrolyte concentration approximately as expected from... 

The theoretical treatment of mass transfer in LSV and CV assumes that only diffusion is operative. Supporting electrolyte concentrations of the order of 0.1 M are generally used at substrate concentrations of the order of 10-3 M, which should preclude the necessity of considering mass transfer by migration. Here, it is assumed that planar stationary electrodes are used under circumstances where diffusion can be considered to be semi-infinite linear diffusion. Other types of electrode may give rise to spherical, cyclindrical or rectangular diffusion and these cases have been treated. 

Even in the solutions of highest resistance given in Table 12.1, the ohmic drop can be calculated to be less than 1 mV for a millimolar solution of electroactive species. In a solvent that does not promote ion pairing, the value of p is, to a first approximation, inversely proportional to the supporting electrolyte concentration. Thus, the ohmic drop in steady-state voltammograms can be adjusted by changing either the concentration of the electrolyte or the electroactive species. 

This column describes the composition of the supporting electrolyte. Concentrations are given In moles per liter wherever possible the entry "KOH 0.1" denotes 0.1 F potassium hydroxide. BrItton-RobInson, Mcllvaine, and other buffers, both mixed and simple, are identified by means of abbreviations. The entry "buffer" means that the solution was said to be buffered at the pH quoted in Column 9 but that no Information was given about the composition of the buffer employed. Maximum suppressors are identified In this column and their concentrations are given in weight/volume per cent. 

Solvent Supporting electrolyte Concentration (M) Reference electrode Limiting low potential (V)... 

The classical version of Frumkin correction includes the initial procedure of Zq determination [iii] from the dependence of current density on the supporting electrolyte concentration at constant electrode charge. 

Parker and Bethell, 1981b. The counter-ion was in all cases BF and the supporting electrolyte concentration was 0.1 M in all cases but Me4NBp4 (sat.)... 

In the case of benzenoid aromatics, values range between 10 and 10 , provided that tetraalkylammonium salts have been used as supporting electrolytes [8b]. In solvents of low dielectricity constant, additional effects are observed, showing influences of the supporting electrolyte concentration and of the nature of the cations [6]. In the tetra-alkylamonium series the strongest (contact) ion pairs are formed by Et N, and Kq is largest for that cation [8b,52]. 

Fig. 20.3. Cyclic Voltammograms illustrating the effect of supporting electrolyte concentration at a 10 NEE for 5 pM TMAFc+ in aqueous NaNOs at concentrations of (1) 1 (2) 10 and (3) 100 mM. Scan rate, 100 mV s (Adapted from Anal.

Why is a high supporting electrolyte concentration used in most electroanalytical procedures ... 

It should be intuitively obvious (and is further clarified below) that the effect of applied potential on the electron transfer rate between the electrode M and a molecular species S in its solution neighborhood reflects the way by which this potential translates into a potential drop between M and S. This follows from the fact that the rate depends on the relative positions of electronic levels in the electrode and the molecule, which in turn depend on this drop. In much of the electrochemical literature it is assumed that when the electrode potential changes by 3 T so does this potential drop. This amounts to the assumption that the species S does not feel the potential change on M, that is, that the electrolyte solution effectively screens the electrode potential at the relevant S-M distance. Such an assumption holds at high supporting electrolyte concentration (order of 1 mole per liter). However, even... 

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