Voltammetry for Electroanalysis

The book gives clear introductions to the theories of electron transfer and of diffusion in its early chapters. These are developed to interpret voltammetric experiments at macroelectrodes before considering microelectrode behaviour. A subsequent chapter introduces convection and describes hydrodynamic electrodes. Later chapters describe the voltammetric measurement of homogeneous kinetics, the study of adsorption on electrodes and the use of voltammetry for electroanalysis. 

Zhang S, Meyer B, Moh GH, Scholz F (1995) Development of analytical procedures based on abrasive stripping coulometry and voltammetry for solid state phase microanalysis of natural and synthetic tin-, arsenic-, and antimony-bearing sulfosalts and sulfides of thalhum, tin, lead, and silver. Electroanalysis 7 319-328. 

Lam, M.T., Chakrabarti, C.L., Cheng, J. and Pavski, V. (1997) Rotating disk electrode voltammetry/anodic stripping voltammetry for chemical speciation of lead and cadmium in freshwaters containing dissolved organic matter. Electroanalysis, 9, 1018-1029. 

Town, R.M. (1997) Potentiometric stripping analysis and anodic stripping voltammetry for measurement of Cu(II) and Pb(II) complexation by fulvic acid a comparative study. Electroanalysis, 9, 407-415. 

Petrovic SC, King DF, and Dewald HD (1998) Electrochemical detection in thin-layer chromatography (TEC). A review on application of direct on-plate square-wave anodic stripping voltammetry for TEC. Electroanalysis 6 393-398. 

We mentioned that polarography is a form of voltammetry in which the electrode area does not remain constant during electrolysis. It is possible, however, to use electrode materials other than mercury for electroanalysis, provided that the potential window available is suitable for the analyte in question. Table 15.7 summarizes the accessible potential ranges for liquid mercury and for solid platinum electrodes. The precious metals and various forms of carbon are the most common electrodes in use, although a great many materials, both metallic and saniconducting, find use as analytical electrode substrates. Voltammetry is conducted using a microelectrode as the WE under conditions where polarization at the WE is enhanced. This is in sharp contrast to both poten-tiometry and coulometry where polarization is absent or minimized by experimental conditions. 

The majority of measurements for electroanalysis with microelectrodes are recorded under steady-state conditions by using either chronoamperometry (CA), linear sweep voltammetry (LSV) or cyclic voltammetry (CV) [1,2, 9,10]. Moreover, to solve problems related to the selectivity between species with similar redox potentials, pulsed techniques such as differential pulse voltammetry (DPV) [1, 7, 43 5] and square-wave voltammetry (SWV) [1, 45-49] have been employed. The use of the latter technique also minimizes the influence of oxygen in aerated natural samples [47]. In order to enhance sensitivity in these measurements, fast-scan voltammetry (FSV) [50] or the accumulation of analytes onto an electrode surface has also been performed, in conjunction with stripping analysis (SA) [51]. 

The properties and applications of microelectrodes, as well as the broad field of electroanalysis, have been the subject of a number of reviews. Unwin reviewed the use of dynamic electrochemical methods to probe interfacial processes for a wide variety of techniques and applications including various flow-channel methods and scanning electrochemical microscopy (SEM), including issues relating to mass transport (1). Williams and Macpherson reviewed hydrodynamic modulation methods and their mass transport issues (2). Eklund et al. reviewed cyclic voltammetry, hydrodynamic voltammetry, and sono-voltammetry for assessment of electrode reaction kinetics and mechanisms with discussion of mass transport modelling issues (3). Here, we focus on applications ranging from measnrements in small volumes to electroanalysis in electrolyte free media that exploit the uniqne properties of microelectrodes. 

In summary, the UME voltammetry that has been performed in RTILs has illustrated the crucial roles that the UME dimensions, the RTIL viscosity (and consequently the diffusion coefficient of the redox species) and the voltammetric scan rate play in such measurements. If one wants to record truly steady-state CVs in RTILs, it is important to consider each effect and, for electroanalysis in especially viscous RTILs, much smaller UMEs may be required to record steady-state currents. 

It is an advantage of electroanalysis and its apparatus that the financial investment is low in comparison, for instance, with the more instrumental spectrometric methods real disadvantages are the need to have the analyte in solution and to be familiar with the various techniques and their electrochemistry it is to be regretted that the knowledge of chemistry and the skill needed often deter workers from applying electroanalysis when this offers possibilies competitive with more instrumental methods (cf., stripping voltammetry versus atomic absorption spectrometry). 

In the laboratory, electroanalysis is used for two main purposes, either for direct measurement of a physico-chemical property that is informative with respect to the identity and/or amount of the analyte, or for detecting the course of conversion of the analyte or indicating the separate appearance of analyte components, which is informative with respect to their identity and amount. In the former instance we are dealing with conductometry, voltammetry and coulometry and in the latter with various titrations and mostly separational flow techniques such as chromatography and flow injection analysis. 

Fiber electrodes -> microelectrodes in a form of bare fibers as the conductive elements, protruding from the end of an insulator, usually made of carbon fibers of 7-8 pm diameter and sealed in glass capillaries often used for direct measurements (e.g., using fast cyclic voltammetry) of the in-vivo release of oxidiz-able neurotransmitters, such as dopamine, serotonin, norepinephrine, or epinephrine, from living cells. Also used to monitor electric activity of single nerve cells or for diagnostic purposes in electroanalysis. S ee also carbon fiber electrode. 

Potentiodynamictechniques— are all those techniques in which a time-dependent -> potential is applied to an - electrode and the current response is measured. They form the largest and most important group of techniques used for fundamental electrochemical studies (see -> electrochemistry), -> corrosion studies, and in -> electroanalysis, -+ battery research, etc. See also the following special potentiodynamic techniques - AC voltammetry, - DC voltammetry, -> cyclic voltammetry, - linear scan voltammetry, -> polarography, -> pulse voltammetry, - reverse pulse voltammetry, -> differential pulse voltammetry, -> potentiodynamic electrochemical impedance spectroscopy, Jaradaic rectification voltammetry, - square-wave voltammetry. 

In analytical investigations in nonaqueous media and aqueous solutions of optimal composition (high concentrations of bases and/or alkaline-earth cations), the electroanalysis provides sufficiently reproducible results, even for relatively unstable YBCO [34]. However, voltammetry in degradation-active media also gives valuable characteristics of the products of the oxide reactions with the medium. 

A study on operational parameters for advanced use of bismuth film electrode in anodic stripping voltammetry. Electroanalysis 14(24) 1707-1712. 

From 1953, much research has been done on the electrochemical behavior of CDs and their inclusion complexes. It is known that the effect of CDs on electrochemical properties of the guest molecules can be used in potentiometry, polarography and voltametry, cyclic voltammetry and amperometry. The ability of CDs to bond, orient and separate molecules and to form inclusion complexes in solution or on modified electrodes can be utilized for electrocatalysis, electrosynthesis and electroanalysis [78]. 

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