Polarization Polarography

From the nature of the process described above it has been referred to as stripping polarography , but the term anodic stripping voltammetry is preferred. It is also possible to reverse the polarity of the two electrodes of the cell, thus leading to the technique of cathodic stripping voltammetry. 

The first version of a polarographic technique was put forward in 1922 by the Czech scientist Jaroslav Heyrovsky. Classsical polarography is the measurement of quasisteady-state polarization curves with linear potential scans applied to the DME sufficiently slowly (v between 1 and 20mV/s), so that within the lifetime, of an individual drop, the potential would not change by more than 3 to 5 mV. With special instruments (polarographs), one can record the resulting 7 vs. E curves (polaro-grams) automatically. 

P. Zuman, Chem. Eng. News, 46 (March 18, 1968) 94 Substituent Effects in Organic Polar-ography, Plenum Press, New York, 1967 Topics in Organic Polarography, Plenum Press, New York, 1970. 

The Model 384B (see Fig. 5.10) offers nine voltammetric techniques square-wave voltammetry, differential-pulse polarography (DPP), normal-pulse polar-ography (NPP), sampled DC polarography, square-wave stripping voltammetry, differential pulse stripping, DC stripping, linear sweep voltammetry (LSV) and cyclic staircase voltammetry. 

A modification of faradaic impedance measurement is a.c. polarography, where a small a.c. voltage is superimposed on the voltage polarizing the dropping mercury electrode (Fig. 5.181). 

The electrochemical behavior of niclosamide was described on the basis of d.c. polarography, cyclic voltammetry, a.c. polarography, and differential pulse polar-ography, in the supported electrolytes of pH ranging from 2.0 to 12.0 [32], A tentative mechanism for the reduction of niclosamide is proposed that involves the transfer of 4 e . Parameters such as diffusion coefficients and heterogeneous forward rate constant values were evaluated. 

We now introduce voltammetry and the subset technique of polarography. The word root voltam- tells us straightaway that we are looking at both potential ( volt- ) and current ( am- ). We will see that during any voltammetry experiment, the potential of an electrode is varied while we simultaneously monitor the current that is induced. This occurs as a result of the electrode being polarized, that is, its potential is forced away from its equilibrium value. 

The concept of polarization is so important that many aspects of this chapter will be discussed in terms of it. Indeed, the root polar- of polarography implies polarization. As a working definition, we say that polarization represents... 

Polarization of light and adsorption, 803 Polarized light. 800. 801. 1147 Polarography, 1237, 1424 activation potential in, 1244 assumptions in, 1244 charge transfer equilibrium, 1240 condition, 1238... 

A perfect prototype of an ideally cation-permselective interface is a cathode upon which the cations of a dissolved salt are reduced. Experimental polarization curves measured on metal electrodes fit the theory very closely. Since in dimensional units the limiting current is proportional to the bulk concentration, the polarization measurements on electrodes may serve for determining the former. This is the essence of the electrochemical analytical method named polarography. (For the theory of polarographical methods see [28]—[30].)... 

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. 

The determination of diazepam in plasma with detection limits of 0.03-0.2 fjLg/mh by cathode ray [189] and pulse polarography [174,190] has been described. The first reported pulse assay [174] differs from the other polarographic assays [189,190] in that a more polar solvent is employed to ensure quantitative extraction, followed by TLC separation and determination of diazepam and its major blood metabolite, N-desmethyldiazepam, to ensure specificity. 

Delahay, JACS 75, 555-59 (1953) (Oscillographic polarography with controlled potential) 3)C.A.Streuli W.D.Cooke, AnalChem 26, 963 70 (1953) (Chronoamperometry with linearly varied potential using polarized Hg pool cathode) 4)P.Delahay, "New Instrumental Methods in Electrochemistry ,Inter science,... 

Polarography has been an extremely valuable electroanalytical method, although its importance has declined in recent years. The life and work of Jaroslav Heyrovsky, the inventor of the technique, was reviewed in the Toronto symposium,94 and also on the occasion of the centenary of his birth.95,96 The 75th anniversary of the discovery of polarography occurred in 1997. On that occasion the son of the inventor gave an account of the studies on the dropping mercury electrode and on the polarization... 

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