Electroanalytical chemistry

In practice, electrochemistry not only provides a means of elemental and molecular analysis, but also can be used to acquire information about equilibria, kinetics, and reaction mechanisms from research using polarography, amperometry, conductometric analysis, and potentiometry. The analytical calculation is usually based on the determination of current or voltage or on the resistance developed in a cell under conditions such that these are dependent on the concentration of the species under study. Electrochemical measurements are easy to automate because they are electrical signals. The equipment is often far less expensive than spectroscopy instrumentation. Electrochemical techniques are also commonly used as detectors for LC, as discussed in Chapter 13. 

Coauthor R.J. Gale, Department of Chemistry, Louisiana State University, Baton Rouge, LA 

Steady-state and pseudo-steady state techniques (d.c. polarography, pulse and differential pulse polarography, a.c. polarography) are especially suitable for analytical purposes, i.e. the determination of the composition of a sample and of concentrations of single species in such a sample. It is less commonly recognized that these techniques are also indispensable for the determination of less interesting properties of the components 

Of growing interest is the application of these methods in the field named speciation , that is the study of the kinds of species in which, for example, a metal is present in an environment containing several complexing ligands. This field concerns not only the determination of stability constants of equilibria, but also of the rates of establishment of these equilibria. This means that the simple theories in Sect. 2 have to be extended by accounting for chemical conversions between electroactive (i.e. reducible or oxidizable) and electro-inactive species, occurring in the diffusion layer region. This subject will be treated in more detail in Sect. 7. 

Generally, sensitivity in the analytical sense is greater if the technique employed is faster, i.e. the electrolysis time is shorter, or the frequency of a periodic electrolysis is higher. Resolution of half-wave potentials, and thus accuracy of standard potentials and stability constants, is better if a derivative technique such as differential pulse polarography, a.c. polar-ography, and, preferably, the second derivative technique second-harmonic a.c. polarography, is employed. 

Similar reasoning may hold if the electroactive species to be determined or studied otherwise can be adsorbed at the electrode surface. Also, in this case, the current—potential relationship is mathematically more complex and shapes and magnitudes (peak heights, limiting currents) of polarograms are more severely affected if the technique is faster (see also Sect. 6). As a consequence, calibration curves may become non-linear and even horizontal (i.e. the quantity monitored is independent of 

It will be almost superfluous to mention that such involved procedures are possible nowadays due to the availability of computerized systems [54, 86—90] which organize the measurements as well as the on-line data analysis. On the other hand, many analytical problems may still be attacked by means of the classical d.c. polarogram and, moreover, many other technical or fundamental improvements of polarographic methods have been introduced during the last decade, as can be inferred from recent textbooks [21, 51). In fact, it is lack of knowledge about theoretical backgrounds of (particular) electrode reactions that hampers the reliable application of electroanalytical techniques, especially in more involved practical systems. 

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J. F. Rusling, in Electrochemistry in Micelles, Microemulsions and Related Microheterogeneous Fluids, Electroanalytical Chemistry, A Series of Advances, Marcel Dekker, New York, 1994. 

Osteryoung J and O Dea J J 1986 Square wave voltammetry Electroanalytical Chemistry ed A J Bard (New York Dekker)... 

Vassos, B. H. Ewing, G. W. Electroanalytical Chemistry. Wiley-Interscience New York, 1983. 

Curran, D. J. Constant-Current Coulometry. Chapter 20 in Kissinger, P. T. Heineman, W. R., eds. Eaboratory Techniques in Electroanalytical Chemistry. Marcel Dekker, Inc. New York, 1984, pp.539—568. 

Laboratory Techniques in Electroanalytical Chemistry. Marcel Dekker, Inc. New York, 1984, pp. 569-607. 

Electroanalytical chemistry is one of the areas where advantage of the unique properties of SAMs is clear, and where excellent advanced analytical strategies can be utilized, especially when coupled with more complex SAM architectures. There are a number of examples where redox reactions are used to detect biomaterials (357,358), and where guest—host chemistry has been used to exploit specific interactions (356,359). Ion-selective electrodes are an apphcation where SAMs may provide new technologies. Selectivity to divalent cations such as Cu " but not to trivalent ions such as Fe " has been demonstrated (360). 

The reference electrode contributes heavily to the economics of electroanalytical chemistry. Companies that sell and service electroanalytical instmmentation are few in number and small in size, or they are parts of much larger companies. One suppHer of electroanalytical instmmentation is Princeton AppHed Research Corp. (PARC) of Princeton, Newjersey. PARC is a subsidiary of EG G Instmments, Inc. Among the many suppHers of ion-selective electrodes are Orion (Boston, Massachusetts), Corning (Corning, New York), and Ingold (Wilmington, Massachusetts). Brinkmann Instmments, Inc. (Westbury, New York) is a useful suppHer of titration equipment. 

Awad, S. A. and Kamel, K. M. Behaviour of Tin as Metal-metal Phosphate Electrode and Mechanism of Promotion and Inhibition of its Corrosion by Phosphate Ions , Journal of Electroanalytical Chemistry, 24, 217-25 (1969)... 

J J Lingane, Electroanalytical Chemistry, 2nd edn, Interscience, New York, 1958 3.1 M Kolthoff and P J Elving, Treatise on Analytical Chemistry, Part I, Vol 4, Wiley,... 

B H Vassos and G W Ewing Electroanalytical Chemistry, John Wiley and Sons, New York, 1983... 

Several international journals bring together papers and reviews covering innovations and trends in the field of electroanalytical chemistry ... 

Many textbooks and reference works dealing with various aspects of electroanalytical chemistry have been published in recent decades. Some of these are given below as suggestions for additional reading, in alphabetic order ... 

W Heineman, F. Hawkridge and H. Blount, Spectroelectrochemistry at Optically Transparent Electrodes in A.J. Bard, Ed., Electroanalytical Chemistry, Vol. 13, Marcel Dekker, New York, 1986. 

Plambeck JA (1982) Electroanalytical chemistry, John Wiley, New York... 

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