Voltammetry alternating current

Alternating current impedance measurements enjoy appreciable application in the study of a diverse range of electrochemical processes including 

Reversible, quasi-reversible and irreversible electrode processes have been studied at the RDE [266] as have coupled homogeneous reactions without [267] and with the effect of electrode kinetics [268], The theoretical results are very similar to those of a.c. polarography, being very phase-angle sensitive to coupled chemical reactions in the rotation speed range where convection can be neglected, the polarographic results may be directly applied [269]. 

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As already stated, other electrochemical techniques have been used to derive thermodynamic data, some of them considered to yield more reliable (reversible) redox potentials than cyclic voltammetry. This is the case, for instance, of second harmonic alternating current voltammetry (SHACV) [219,333], Saveant and co-workers [339], however, concluded that systems that appear irreversible in slow-scan CV are also irreversible in SHACV experiments. We do not dwell on these matters, important as they are. Instead, we concentrate on a different methodology to obtain redox potentials, which was developed by Wayner and colleagues [350-352]. 

M. R. Wasielewski, R. Breslow. Thermodynamic Measurements on Unsubstituted Cyclopropenyl Radical and Anion, and Derivatives, by Second Harmonic Alternating Current Voltammetry of Cyclopropenyl Cations. J. Am. Chem. Soc. 1976, 98, 4222—4229. 

C. P. Andrieux, P. Hapiot, J. Pinson, J.-M. Saveant. Determination of Formal Potentials of Chemically Unstable Redox Couples by Second-Harmonic Alternating Current Voltammetry and Cyclic Voltammetry. Application to the Oxidation of Thiophenoxide Ions. J.Am. Chem. Soc. 1993,115, 7783-7788. 

Equation (7.116) indicates that the charge-potential curves for reversible processes are only dependent on the square wave amplitude Sw and are independent of the frequency / = 1 jh and the staircase amplitude AEs. As a consequence, they are superimposable on those obtained at any differential electrochemical technique, such as DSCVC, provided that the differences between the successive potential pulses coincide (AE = 2 sw)- Moreover, when this difference is much less than RT/F (i.e., less than 25 mV at T = 198 K), the responses obtained in Cyclic Voltammetry (CV), Alternating Current Voltammetry, Potentiometric Stripping Analysis (PSA) and also in any Reciprocal Derivative Chronopotentiometry (RDCP) fulfill [5, 74, 75] ... 

Chapter 9) or potential pulses (Chapter 10) alternating current voltammetry (Chapter 11) and so on. Additionally, kinetic and mechanistic information can sometimes be obtained from the same set of experiments. 

I.2.4.3 Differential Pulse Voltammetry (DPV), Alternating Current Voltammetry (ACV), and Square-Wave Voltammetry (SWV)... 

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... 

SWV is a very sensitive technique partly because of its ability to discriminate against charging current [70-74]. However, a specific adsorption of reactant may significantly enhance SWV peak currents [75, 76]. Unlike alternating current voltammetry, SWV effectively separates a capacitive current from a so-called pseudocapacitance [77]. This is the basis for an electroanalytical application of SWV in combination with an adsorptive accumulation of analytes [78-81],... 

Despite the dependence of ip on charge-transfer kinetics (eqns [5] and [6]), the sensitivity of LSV is almost independent of the reversibility degree (only a decrease of 25% is found on passing from a Nernstian to a totally irreversible process with a = 0.5). This fact makes LSV the most sensitive voltammetric technique for analytes involved in irreversible processes because pulsed voltammetric methods or alternating current voltammetry provide for these processes very low signals. 

Note HRP Horseradish peroxidase TMB Tetramethylbenzidine ACV Alternating-current voltammetry amole le-18 moles DPV DifTerential pulse voltammetry E Detection limit for unconjugated enzyme E Detection limit for conjugated (Ab/Ag) enzyme FIA-EC Flow-injection analysis with electrochemical detection CC Classy carbon LC-EC Liquid chromatography with electrochemical detection P Detection limit for final enzymatic product P Detection limit for standards of P RDE Rotating disk electrode SPE Screen-printed electrode SQV Square-wave voltammetry zmole le-21 moles. 

For SAMs with attached redox molecules, k (units of s ) can be measured by cychc voltammetry, chronoamperome-try (CA), alternating current impedance spectroscopy (ACIS), alternating current voltammetry (AGV), AG electroreflectance spectroscopy, and an indirect laser-induced temperature (ILIT) jump method. 

A large number of potential-relaxation and current-relaxation techniques have been developed in 1950s-1980s for fast kinetic measurements (8). The later advances in UMEs resulted in a less frequent use of relaxation techniques in kinetic experiments. Because of the space limitations, only one large-perturbation method (sampled-current voltammetry) and one small-perturbation technique (alternating current voltammetry) will be considered. 

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