Anodic Waves measurement

In the presence of 6-iodo-l-phenyl-l-hexyne, the current increases in the cathodic (negative potential going) direction because the hexyne catalyticaHy regenerates the nickel(II) complex. The absence of the nickel(I) complex precludes an anodic wave upon reversal of the sweep direction there is nothing to reduce. If the catalytic process were slow enough it would be possible to recover the anodic wave by increasing the sweep rate to a value so fast that the reduced species (the nickel(I) complex) would be reoxidized before it could react with the hexyne. A quantitative treatment of the data, collected at several sweep rates, could then be used to calculate the rate constant for the catalytic reaction at the electrode surface. Such rate constants may be substantially different from those measured in the bulk of the solution. The chemical and electrochemical reactions involved are... 

This conclusion was supported by coulometry measurements that showed that the charge passed during the growth was typically c. 9 or 10 times that under the anodic wave of the voltammogram up to the potential corresponding to the maximum doping level (cf. Schemes 3.9 and 3.10). 

The equilibrium between mercaptans and a,fl-unsaturated ketones (9) can be followed by measuring the cathodic waves of the unsaturated ketones, or of the p-mercaptoketones formed, or by measuring the anodic waves of the mercaptans (73). 

Taking account of the charge associated with peak IIIa, this implies that about 1 pC of the 5 pC of peak Ic measured in scan 20 is still due to gold oxide reduction, corresponding to 95% CoTSPc coverage. Therefore, it can be concluded that peaks Ic and IIIa in scan 20 are related to the same reversibly behaved redox system. Reversibility can be proven by the fact that the half-wave potentials for both waves are the same, and that the peak potential for the anodic wave (IIIa) does not shift with scan number. 

In addition to observations on the ketone and adduct it is possible to measure the anodic waves of mercaptans. 

All potentials are given in volts vs SCE and all measurements were carried out in acetonitrile solutions -0.3N in NEt BF. The number in parentheses indicates the difference in potential for the peak current for the cathodic and anodic waves. See Legend of Symbols at end of paper for ligand abbreviations. 

A measurement of host-guest interaction has been made with an anodic wave polarography in the same manner as those previously applied to the complexation of polycarboxylate [15] and catechols with [18]aneN6 [16]. The final results along with the Ki values used for calculation are summarized in Table II. 

If the shape of the wave shows a reversible process, when the limiting current is diffusion controlled, but the half-wave potentials differ from those measured at the equilibrium conditions and are dependent on the drop-time ( x/2 = const. 2-303RTInFlogiff, then the product of the reversible electrode reaction is inactivated by a fast chemical reaction, e.g. in the case of the anodic waves for ascorbic acid.< > > It was supposed that the inactivation reaction is the hydration of dehydroascorbic acid, but the polarographic behaviour of dehydroascorbic acid does not agree with this simple explanation. 

If the sample is a complicated mixture, it depends on the nature and ratio of the single constituents whether or not a polarographic method is preferable. It is a simple problem in polarography to determine a trace constituent that is reduced at more positive potentials (A) than an excess of a reducible compound (B) (Fig. 22, curve 1). Similarly a small anodic wave at more negative potentials (C ) can be measured exactly in the presence of excess of a substance (D ) which gives a large anodic wave at more positive potentials (Fig. 22, curve 4). 

Then inspect the resulting curves to discover whether there is a cathodic or an anodic wave and in what pH-region. When a reduction wave is obtained make sure that it does not change with time, measured at 10 and 20 min intervals. Then study the dependence of the concentration of the depolarizer, as well as the effect of the mercury pressure, to obtain information concerning the character (the type) of the electrode process involved. Such measurements are even more important for systems, where two or more waves are observed simultaneously on a polarographic curve at different potentials. Follow also the changes in the ratio of the two waves with the parameters mentioned above. 

Carbon disulphide gives a reduction wave, but owing to its volatility and low solubility in aqueous solutions, the oxygen is not easily removed from its solutions. Thus an indirect method was used, ) based on the introduction of the sample containing carbon disulphide into an ethanolic solution of diethylamine. The anodic wave of the diethyl dithiocarbamate formed is measured. The procedure for the analysis of gaseous samples is as follows ... 

Procedure. Dilute 1-2 ml. of gasoline 20 to 50 times with ethanol. Add sulphuric acid so as to make the final concentration 0-025 N, and add 0-05 ml. of a 3 per cent solution of cadmium nitrate (to remove the sulphide ions present). Then dilute the solution to a certain volume with water and ethanol so as to make the final concentration of ethanol 85-90 per cent. Finally, measure the anodic wave at —0-02 V. 

The cyclic voltammetry of a film formed on a Pt electrode reveals a highly reversible redox system. The cyclic voltammogram is highly symetric (IpJIpc 1-18) and the separation between the cathodic and anodic peaks is low ( pa — pc 60 mV) (Figure 14.32). The doping level, y, deduced from coulometric measurements has a value very close to that obtained for poly(3-heptylthiophene), respectively y = 0.15 and y = 0.16. At low scans, the anodic wave shows two components at 0.62 V and 0.8 V The fact that these potentials are slightly less anodic than those of poly(3-heptylthio-... 

---