Constant-potential coulometry

Chloramphenicol, a broad-spectrum antibiotic, has probably received more attention in the polarographic literature than any other pharmaceutical. The aromatic nitro group is quite easily reduced. Studies [76] employing polarog-raphy, cyclic voltammetry, and constant-potential coulometry have suggested that... 

Constant-potential coulometry is related to industrial electroplating ... 

E630 Jacobs, J.C. and Alexander, N.M. (1990). Colorimetry and constant-potential coulometry determinations of transferrin-bound iron, total iron-binding capacity, and total iron in serum containing iron-dextran, with use of sodium di-thionite and alumina columns. Clin. Chem. 36, 1803-1807. 

Reactions of hydrazine (N2Hs ), phenylhydrazine (N2H4Ph ) at pH 2.8 and azide (Nj-) at pH 5.3 with [Ru (HL)(H20)] and [Ru "L(H20)] (where L = ethylenediamminetetraacetate) were studied by voltammetry and spectrophotometry at 25 °C. The resultant complexes were electrolyzed in the presence of nitrogenous ligands in excess by constant potential coulometry at Hg-pool electrode. The turnover rates for the formation of ammonia and/or amine and the catalytic efficiency of these nitrogenous compounds were reported. An appropriate mechanism for the catalytic reduction of hydrazines and azide were proposed. 

Constant potential coulometry allows better control as electrode reactions are always governed by the electrode potential. Interfering reactions can be avoided as long as their redox potentials are sufficiently distinct. It may also be possible to... 

Figure 2 Current decay on a logarithmic scale during constant potential coulometry.

Constant potential coulometry requires the presence of a reference electrode in solution, besides working and counter-electrodes, and the use of a potentiostat in order to accurately set the applied potential (see Figure 4). 

Constant-potential coulometry [37,49] is presently employed to some extent for determining serum iron. Current generated at two electrodes with potentials of 460 and 325 mV is measured. Copper is reduced at both of them, while iron reduction occurs at one electrode (325 mV), so that copper can be blanked out. Iron-dextran (Imferon), sulfasalazine, and pyrazinamide interfere in this assay [37,49]. Iron-dextran is not detected in the dry-film Kodak assay for iron [49,55]. 

In this section the theory and methodology of electro-analytical chemistry are explored. Chapter 22 provides a (general foundation for the study of subsequent chapters in this section. Terminology- and conventions of electrochemistry as well as theoretical and practical aspects of the measurement of electrochemical potentials and current s are. presented. Chapter 23 comprises the many methods and applications of potentiometry. and constant-potential coulometry and constant-current coulornetrv are discussed in Chapter 2 4. The many facets of the important and widely used technique of voltammetry are presented in ( hapter 2.5. which concludes the section. 

In the preceding section, we mostly considered cases wherein only a thin segment of the electroactive region (whether the solution or the film phase) was electro-chemically altered. This situation must be contrasted with those in which exhaustive electrolysis is involved. An example is constant-potential coulometry (Fig. 20.4) wherein the entire solution contained within the cell is electrolyzed. As mentioned earlier, this is ensured by the use of a large A/V ratio and efficient solution agitation. The underlying coulometric equation derives from Faraday s law of electrolysis and can be expressed as... 

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