Harmonic alternating current

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. 

Smith, D.E., and W. H. Reinmuth Second Harmonic Alternating Current... 

By using phase selective measurement of a higher-harmonic alternating current (e.g., 2nd harmonic with a frequency 2j) increased sensitivity (lO mol/L) is obtained because of the marked reduction in the capacitive current component of the higher harmonic (AC2 or second harmonic wave polarography). 

Bond AM, O Halloran RJ, RuziC I, Smith DE (1976) Fundamental and second harmonic alternating current cyclic voltammetric theory and experimental results for simple electrode reactions involving solution-soluble redox couples. Anal Chem 48 872. 

Large amplitude Fourier transformed high harmonic alternating current cyclic voltammetry kinetic discrimination of interfering faradaic processes at glassy carbon and at boron doped diamond electrodes, J. Zhang, S.-X. Guo, and A. M. Bond, Anal. Chem., 2004, 76, 3619. 

Many electrical problems, or problems associated with the quality of the incoming power and internal to the motor, can be isolated by monitoring the line frequency. Line frequency refers to the frequency of the alternating current being supplied to the motor. In the case of 60-cycle power, monitoring of the fundamental or first harmonic (60 Hertz), second harmonic (120 Hz), and third harmonic (180 Hz) should be performed. 

Faradaic rectification — When the electrode potential of the working - electrode is modulated with a sinusoidal -> alternating current the mean potential is shifted from the DC value by a small increment in many cases when the AC modulation is sufficiently large. This effect has been named faradaic rectification, it is caused by the nonlinearity of the electrode response, in particular the variation of current with electrode potential [i]. A theoretical treatment for an electrode in contact with a solution containing a redox system has been provided [ii]. It was extended to reactions where one reactant is present in its element form dissolved in the liquid metallic phase (e.g., Cd2+ + 2e -> Cd(Hg)) [iii]. An improved evaluation technique has been proposed [iv], and some inherent problems have been reviewed [v]. A variant of this method applied to -> polarography has been described [vi]. Second and higher harmonics in - AC voltammetry (polarography) [vii] also arise from this nonlinearity, and hence these techniques also have some characteristics that resemble those found in - faradaic rectification voltammetry. 

Second harmonic — Any nonlinear oscillating system produces higher harmonic oscillations. The second harmonic is the response having twice the frequency of the basic oscillation. The - current response of a faradaic electrode reaction (- faradaic reaction) to perturbations of the - electrode - potential is generally nonlinear, and thus higher harmonic oscillations of the - alternating current (AC) are produced in - AC voltammetry. Since the -> capacitive current is a much more linear function of the electrode potential, the capacitive contribution to higher harmonic currents are rather small which allows a desirable discrimination of theses currents in electro-analytical applications. 

A. Current Variability and Harmonics. The function of a rectifier system is to convert a power supply received as alternating current into the direct current required by the cells. There may be a reduction in voltage through transformers prior to the rectifiers, but this is outside the scope of the present discussion. Within the rectifier system, there will be some reduction in voltage to match the varying demands of the... 

Mashkina, E. and Bond, A.M. (2011) Implementation of a statistically supported heuristic approach to alternating current voltammetric harmonic component analysis re-evaluation of the macrodisk glassy carbon electrode kinetics for oxidation of ferrocene in acetonitrile. Analytical Chemistry, 83,1791-1799. 

If the signal is an alternating current sine wave, being at either of the nonlinear ends of the characteristic curve will cause "distortion" of the waveform shape. This causes the formation of "harmonics" of the original frequency, so the linearizing effect of a bias is quite important in such low-distortion applications as audio amplifiers. 

The abilities of alternating current polarography, including secmid harmonic polarography, etc., have been widely utilized in our laboratory to achieve very low detection limits (10 and 10 mol L ) based on their adsorption/desorption behavior. 

The protection current produced by the usual full-wave rectifier has a 100-Hz alternating component of 48%. There are receivers with selective transmission filters for 100 Hz, which corresponds to the first harmonic of the cathodic protection currents [45]. With such a low-frequency test current, an inductive coupling with neighboring pipelines and cables is avoided, which leads to more exact defect location. 

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