Electroactive organic compounds

For the analysis of surface-active, electroactive organic compounds, the adsorptive stripping SWV was used. The method was applied to numerous analytes. Several of them are listed in Table 3.2. Some examples of metal complexes which were used for the quantitative analysis of metal ions by adsorptive... 

As discussed elsewhere (212), the one-electron oxidation or reduction of, e.g., unsaturated hydrocarbons or other electroactive organic compounds and ions [Eqs. (37a)-(37d)] creates radical cations, radical anions, or radicals with an energy content, which surmounts that of the original substrate... 

Figure 1 Effect of pH on 1/2 values of three pairs of closely related electroactive organic compounds.

Major areas of electrochemical measurements with CPEs (in order of appearance) (1) Electrode reaction pathways and mechanisms of electroactive organic compounds (see also Figure 11.3a-d) (II) Pharmaceutical and clinical analysis (III) Solid-phase voltammetry with electroactive CPEs (IV) Analysis of (i) inorganic ions and molecules, (ii) organic compounds -i- environmental pollutants, and (iii) analysis of biologically important compounds (BICs) (V) Voltammetry in vivo (also known as brain electrochemistry). 

Ion chromatography is used to perform separation and detection of inorganic anions and cations, organic acids, and electroactive organic compounds. This instrument may be configured with a variety of detectors such as conductivity, pulsed electrochemical, and UV-visible detectors. Applications include the determination of anions in electronic-grade materials, residual organic acid in polymers and copolymers, and blend formulations. 

North Sea water at the natural pH has a complexing capacity, probably due to the presence of dissolved organic compounds, in a concentration equivalent to 0.3 M copper. The complexing capacity is zero at pH 2.7. The method of standard addition for the determination of electroactive copper and lead concentrations may lead to erroneous results in samples where complexation of this type occurs. 

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. 

Since the invention of d.c. polarography [10, 11], numerous inorganic and organic compounds have been studied by means of this method in Heyrovsky s school and extensive knowledge gathered about the electrochemical properties of these compounds. Among them, many cases were discovered where the polarographic wave appeared to be influenced by the existence of chemical equilibria between the electroactive substance and other, in most cases electroinactive, species in the electrolyte solution, more particularly by the finite rate at which these equilibria relax after the electrochemical perturbation. In fact, the chemical reaction serves as either a source or a sink to deliver or to consume the electroactive reactants and products, in addition to diffusion. 

In this case, the duplex formation is commonly detected in connection with the use of appropriate electroactive hybridization indicators such as cationic metal complexes (Co(phen)33+, Co(bpy)33+, [Cu(phen)2]2+, Ru(bpy)32+ among others [18-22,32]), or organic compounds (anthracyclines, phenoth-iazine, etc. [15,24,25,28,29]). These compounds interact in different ways with ss- or dsDNA but preferentially with dsDNA undergoing reversible... 

Electrochemical biosensing of DNA sequences using direct electrochemical detection of DNA hybridization, adsorptive striping analysis, metal complex hybridization indicators, organic compound electroactive hybridization indicators and renewable DNA probes have been considered [65,67,72,73]. With metal complexes and organic compound electroactive hybridization indicators, non-specific adsorption can influence the results [68,94]. Chrono-potentiometric detection was used to monitor the hybridization onto screen-printed carbon electrodes by following the oxidation of the guanine peak, which decreases in the presence of the complementary strand [64,68,73]. 

Polarographic determination, by itself, is generally not specific for a particular organic compound. Usually the determination is, in practice, of a particular electroactive group and hence of a class of compounds. 

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