Ring electrodes oxidant concentration

Figure 3.14 Experimental collection efficiencies (Nexpti) at the rotated-ring electrode as a function of HOOH concentration for the product from the oxidation of HOOH at the rotated-disk electrode. Control conditions for GC ring-disk electrode rotation rate, 4900 ipm ED, +2.6 V versus SCE ER, +0.1 V versus SCE.

Pseudo-first-order rate constants, fci (normalized to unit substrate concentration IS]), were determined from current-collection-efficiency data (02 decay rates) with a glassy-carbon-glassy-carbon ring-disk electrode that was rotated at 900 rpm. (O2 was produced at the disk electrode from dissolved O2, which reacted with 2 mM substrate, and the unreacted O2 was determined by its oxidation at the ring electrode.)... 

The value of m is dependent upon the pH of the solution. If m 0, then redox reaction involves the incorporation and expulsion of protons during the redox reaction and this can be measured by a pH-sensitive bismuth oxide ring electrode [18,19]. In the special case when the ring electrode is a potentiometric sensor with a low exchange current density, such as the bismuth oxide sensor for pH [18,19], the ring electrode reaction does not significantly perturb the radial concentration profile of the disc product across the ring, and a different collection efficiency, termed the detection efficiency. 

The selectivity for monitoring DA in the presence of its metabolite DOPAC is increased following electrochemical oxidative pretreatment in pH 7.4 citrate-phosphate buffer. Structurally small carbon ring electrodes can be used to monitor the concentration of DA in the cytoplasm of single cells. Transport (uptake) of exogenous DA into the DA neuron of Planorbis corneus has been monitored intracellularly. Intracellular endogenous DA levels following extracellular application of ethanol have also been monitored. These experiments permit estimation of stored DA levels in the cell body of this neuron. 

This reorganisation also explains the decrease of the current of reduction peak IVC and the formation of the third oxidation peak (IVa). However, both peaks and also peak IIIC are too large to be explained by reduction or oxidation of adsorbed Co(II)TSPc only. It is assumed that this is the result of an electrocatalytic reaction, such as reaction with Co(II)TSPc in solution. This is confirmed by the fact that these peaks disappear when the Co(II)TSPc-modilied gold electrode is scanned in a pH 12 buffer in the absence of Co(II)TSPc in solution. In addition, the peak currents of peak IIIC in the first scan and peaks IIIC and IVC at the scan of maximum coverage vary linearly with Co(II)TSPc concentration (Fig. 7.5). Note that small peaks are observed at the same potentials where peaks IIIC and IVC occurred with solutions containing Co(II)TSPc. Electrochemical measurements of TSPc without Co show also a reduction wave at these potentials, explaining the ring reduction of CoTSPc in solution. This confirms the fact that Co(II)TSPc is adsorbed at the surface of the electrode and electro-catalyses the oxidation/reduction of Co(II)TSPc transported from solution towards the electrode surface. 

The success of the polymerization depends on the solvent used for the process. Most studies of electropolymerized MPc have concentrated on the electrochemical polymerization of MPc(NH2)4 complexes [89-93], The polymerization process of these complexes involves the oxidation of the amino group forming radicals which attack phenyl rings of neighboring molecules [93], The formation of the polymers of (OH)MnPc(NH2)4 and OTiPc(NH2)4 on glassy carbon electrode (GCE) was successfully achieved via electropolymerisation of these complexes in DMF by repetitive scanning at a constant scan rate of 0.1 Vs-1. Simple adsorption of the monomer onto carbon electrodes (using MnPc derivatives) has been reported [94],... 

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