Classical polarography

The major defects of classical polarography are as follows (1) it is not possible to increase the sensitivity drastically, owing to interference from DME charging currents ... 

Under optimum conditions LPS voltammetry is an order of magnitude more sensitive than polarography (i.e., the detection limit is about 10 M). As in classical polarography, somewhat higher sensitivity and selectivity can be attained when using a differential version (i.e., when recording, as a function of potential, not the current but its derivative with respect to potential). 

At one time, voltammetry (particularly classical polarography) was an important tool for the... 

Classical polarography is not optimised for analytical sensitivity. This inefficiency has been remedied in pulse polarography. Instead of applying a steadily increasing voltage on the mercury droplet, in pulse... 

In many respects, differential pulse voltammetry is more similar to classical polarography than to the normal pulse methods (see above). A linear potential ramp of dE/dt is applied to the working electrode (see Figure 6.24). However, in common with normal pulse voltammetry, a succession of pulses are also applied to the working electrode. (The WE is often a DME, and then we refer to differential pulse polarography .)... 

Several types of electroanalytical techniques may be used to gain knowledge concerning the reaction mechanism of an electrolytic reaction and to determine the optimal conditions for an electrosynthesis. The use of classical polarography was illustrated in part I.1 The different electroanalytical techniques have been treated comprehensively in a monograph,9 and the use of... 

This dependence may be useful in search of potential radiosensitizers. Determined with the help of pulse radiolysis, the thermodynamic potentials of one-electron reduction of 2-, 4-, and 5-nitroimidazoles (pH 7) have a higher negative values than those obtained by classical polarography (pH 7.4) [946], Probably, it is generated by the fact that the process of electrochemical reduction involves irreversible stages of the decomposition of nitroimidazole anion radicals. The correlation of E (and E1/2) of nitroimidazoles and their radiosensitizing properties is discussed. With E7 values the correlation is found to be better [946],... 

The electron affinity of 3-(iV-methylpiperazino)-5-nitroindazole, 3,5-dinitroindazole, and molecular complex of the last with water is discussed on the basis of their half-wave potentials and in connection with their eventual radiosensitizing properties [667], The mechanism of EC behavior of 2-substituted 5(6)-nitrobenzimidazoles in acetonitrile has been investigated by classical polarography, cyclic voltammetry, and platinum rotating disk electrode with a ring (RDER) [888,991], It is shown that... 

The electrochemical behavior itself 5(6)-nitrobenzimidazole is investigated depending on media pH by classical polarography [992-994], constantly current, and variable current [995, 996], The reduction 5(6)-nitro-2-arylbenzimidazoles is carried out in DMF and H20/DMF media [997], The polarography was utilized in a study of the influence of 5(6)-nitrobenzimidazole on corrosion-electrochemical behavior of chromos steel [998],... 

The methods of metal analysis described in this chapter can be employed with the highest sensitivity and accuracy of classical polarography (about 50 jag 2%, at higher concentrations 1%). 

For the estimation of traces of proteins in nucleic acid preparations, a pulse polarographic method is more suitable than classical polarography... 

Logarithmic analyses can be carried out on the neopolarogram in much the same way as with classical polarography (see Sec. V). Examples that illustrate the application of the convolution technique include reversible dimerization of radical cations [114], the study of dissociative electron transfer reactions [175,176], and investigations of the possible potential dependence of the transfer coefficient a [174,177]. 

The postulated intermediate, the imine, can in most cases not be isolated or detected by classic polarography. The reduction of 2,4-dihydroxybenzophenone oxime occurs [87], however, in two steps, and reduction at the potential of the first wave produced the imine, which in this case was sufficiently stable to permit its isolation. 

The detection limit for classical polarography is about I O - M. Routine determinations usually involve concentrations in the mM range. 

The detection limits for differential pulse polarography are two to three orders of magnitude lower than for classical polarography. 

One advantage of the derivative-type polarogram is that individual peak maxima can be observed for substances with half-wave potentials differing by as little as 0.04 to 0.05 V in contrast, classical polarography requires a potential difference of about 0.2 V for resolution of waves. 

The greater sensitivity of differential pulse polarography can be attributed to two sources an enhancement of the faradaic current or a decrease in the non-faradaic charging current. To account for the enhancement, consider the events that must occur in the surface layer around an electrode as the potential is suddenly increased by 50 mV. If a reactive species is present in this layer, there will be a surge of current that lowers the reactant concentration to that demanded by the new potential. As the equilibrium concentration for that potential is approached, however, the current decays to a level just sufficient to counteract diffusion (that is, to the diffusion-controlled current). In classical polarography, the initial surge of cur-... 

Chapters 18, 19, 20, and 21 on electrochemical cells and cell potentials have been extensively revised to clarify the discussion and introduce the free energy of cell processes. Chapter 23 has been altered to decrease the emphasis on classical polarography. It now includes a discussion of cyclic voltammetry. 

Feroci, Fini, Badiello, and Breccia [97FER/FIN] studied the complex formation between and SeO by classical polarography in 0.15 M NaN03. They found no evidence for an interaction, see Appendix A. The review estimates from an assumed accuracy of the polarographic measurement of 2 mV, the equilibrium constant of the reaction ... 

The interaction between the selenite or selenate ion with Cu and Pb was studied by classical polarography. The measurements were carried out in unbuffered solution with 0.15 M NaN03 added as supporting electrolyte. The temperature is not mentioned. The... 

At higher concentrations of the electroactive species, adsorption of components of the redox couple, coupled with the fluidity of the liquid-liquid interface, may lead to mechanical streaming of the solution at the interface, generating a polarographic maximum. Charging currents and polaro-graphic maxima typically limit classical polarography to concentrations of the electroactive species between 10 3 and 10 5 M. 

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