Applications of Square-Wave Voltammetry

Finally, SWV was used for the detection of heavy metals in thin-layer chromatography [118] and various organic substances in high-performance liquid chromatography [119]. 

If reaction (II.3.1) is kinetically controlled, the Butler-Volmer equation applies  

The current is determined by Eq. (II.3.45), with the initial and boundary conditions  

The maximum chronoamperometric response is defined by the first derivative of 

This derivation shows that, for any electrode potential E, there is a certain dimensionless kinetic parameter Xmax which gives the highest response (Eq. II.3.76). The maximum of Xmax (Eq. II.3.79) is a parabolic function of the transfer coefficient 0.5 Xmax.max 1, for 0 Qf l.Ifo = 0.5, then Xmax.max = 0.5 and 

SWV has been applied in numerous electrochemical and electroanalytical measurements [2,6,7]. Apart from the investigation of charge transfer kinetics of dissolved zinc ions [40,42] and adsorbed organic species mentioned above 

The convolution integrals in Eqs. (IL3.A10) and (IL3.A14) can be solved by the method of numerical integration proposed by Nicholson and Olmstead [38, 121]  

For numerical integration, Eqs. (II.3.A36)-(II.3.A38) are transformed into a system of recursive formulae [93]  

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Krause MS, Ramaley L (1969) Analytical application of square wave voltammetry. Anal Chem 41 1365-1369. 

Fung, Y. S. and S. Y. Mo. 1992. Application of square-wave voltammetry for the determination of ascorbic acid in soft drinks and fruit juices using a flow-injection system. Anal. Chim. Acta 261 375-380. 

The use of pulse techniques for electroanalytical determinations has been much publicized, and is applicable to both solid electrodes and the HMDE/SMDE. The development in recent years of square wave voltammetry (SWV)39 widens the possibilities beause of its rapidity (Section 10.9) it is especially useful because the time necessary to do an experiment is only 2 s, which means that a SMDE drop in the dropping mode can also be used for micromolar determinations. Progress obtained with pulse techniques40,41 has meant that applications of a.c. voltammetry have been few, but there is no theoretical reason for this. The very low detection limits achieved in stripping voltammetry result not only from the pre-concentration step but also from the use of pulse waveforms in the determination step. 

Application of adsorptive stripping analysis to the determination of nucleic acids at mercury electrodes has also been reported [195]. Tomschik etal. [196] have studied reduction and oxidation of peptide nucleic acid and DNA at mercury and carbon electrodes. The authors have utilized cyclic and square-wave voltammetries to study reduction and oxidation signals of single-stranded peptide nucleic acid and DNA decamers and pentadecamers. 

Gulaboski R, Mirceski V, Komorsky-Loviic S, Lovric M (2004) Square-wave voltammetry of cathodic stripping reactions, diagnostic criteria, redox kinetic measurements, and analytical applications. Electroanalysis 16 832-842. 

The detection limit for TLV has been improved substantially by using differential pulse and square-wave voltammetry (Chap. 5). For example, detection limits in the 10 8 M range and below have been demonstrated in thin-layer cells requiring less than 100 /xL of sample [61,62]. One practical application of twin-electrode thin-layer cells is in the automatic electrochromic rearview mirror for automobiles. A cell with optically transparent electrodes is placed in front of a mirrored surface. At night, electrolysis in the cell to generate colored material can rapidly reduce glare from following vehicles. 

This chapter analyzes the subtractive techniques Differential Multipulse Voltammetry (DMPV), Differential Staircase Voltammetry (DSCVC), and Square Wave Voltammetry (SWV). Of these, the most employed SWV will be analyzed in more detail. Interesting alternatives to DSCVC and SWV are Differential Staircase Voltcoulometry (DSCVC) and Square Wave Voltcoulometry (SWVC), which are based on the analysis of the difference of converted faradaic charge signals obtained between two successive potential pulses when a staircase potential or a square wave potential is applied [4, 5], which is very useful for the study of surface-confined redox species. There exists, however, a book in this series devoted entirely to the theory and application of SWV [6], so in some of the reaction mechanisms analyzed, the reader will be directed to this title for a more thorough treatment of the SWV response. 

Fig. 10.11. Square wave voltammetry, (a) Scheme of application of potentials sum of a staircase and a square wave (b) Typical response st 2mV Tmjn = 2 ms. Note the similarity to DPV.

Applications of pulse techniques in electrochemistry have been predominantly in the area of analysis, relying on the linear dependence of peak height on potential, although recently their use in mechanistic studies, particularly square-wave voltammetry, has begun to be exploited. The reason for their use in analysis is intimately linked with the low detection limits that are attainable, particularly in combination with pre-concentration techniques, as will be seen in Chapter 14. Finally, since nowadays the pulse sequences are generally controlled and responses analysed using microprocessors, the development of new waveforms for particular situations is now a much easier task than it was even a decade ago. 

Masarik M, Kizek R, Kramer K), et al. Application of avidin-biotin technology and adsorptive transfer stripping square-wave voltammetry for detection of DNA hybridization and avidin in transgenic avidin maize. Anal. Chem., 2003 75(11) 2663-2669. 

We will consider five subtopics tast polarography and staircase voltammetry, normal pulse voltammetry, reverse pulse voltammetry, differential pulse voltammetry, and square wave voltammetry. Tast polarography, normal pulse voltammetry, and differential pulse voltammetry form a sequence of development rooted historically in polarography at the DME. To illustrate the motivating concepts, we will introduce each of these methods within the polarographic context, but in a general way, applicable to both the DME and SMDE. Then we will turn to the broader uses of pulse methods at other electrodes. Reverse pulse voltammetry and square wave voltammetry were later innovations and will be discussed principally outside the polarographic context. 

If the concentrations of the redox compounds in the solution or at the electrode surface are low, and better sensitivities are needed than those optimal for LSV and SCV, differential pulse (DPV), normal pulse (NPV) and Osteryoung square-wave voltammetries (OSWV) are more suitable [9a, 9b]. They allow better elimination of the capacitive/background currents and, therefore, the measurement of smaller faradic signals becomes easier. This is achieved either by sampling the current at the end of each pulse (OSWV, NPV) (Fig. 10.5.IE and F) or twice at the end and before pulse application (DPV) (Fig. 10.5.ID). 

For reversible systems there is no special reason to use these techniques, unless the concentration of the electrochemical active species is too low to allow application of DCP or cyclic voltammetry. For a reversible electrochemical system, the peak potentials in alternating current voltammetry (superimposed sinusoidal voltage perturbation) and in square-wave voltammetry (superimposed square-wave voltage... 

Several coulometric and pulse techniques are used in electroanalytical chemistry. Rather low detection limits can be achieved, and kinetic and transport parameters can be deduced with the help of these fast and reliable techniques. Since nowadays the pulse sequences are controlled and the data are collected and analyzed using computers, different pulse programs can easily be realized. Details of a wide variety of coulometric and pulse techniques, instrumentation and applications can be found in the following literature controlled current coulometry [6], techniques, apparatus and analytical applications of controlled potential coulometry [7], coulostatic pulse techniques [8], normal pulse voltammetry [9], differential pulse voltammetry [9], and square-wave voltammetry [10]. 

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