Normal pulse voltammetry adsorption

Normal pulse voltammetry is very sensitive to adsorption of both the substrate and the product at the electrode surface. If the substrate is adsorbed, a peak-shaped voltammogram is obtained. The stronger the adsorption or the lower the concentration of the substrate or the shorter the pulse time, the better defined is the peak. This is illustrated in Fig. II.2.6 by the normal pulse voltammograms of imida-zoacridinone. This compound, at -0.4 V, is strongly adsorbed at the mercury surface, therefore the two consecutive reduction steps result in the formation of two peaks instead of two waves. 

Differential normal pulse voltammetry. As presently used, in this waveform each pulse corresponding to NPV (see Fig. 5a) is divided into two equal parts with a small increase in potential in the second half of the pulse. The difference between the currents sampled halfway through and at the end of the main pulse is displayed as a function of the potential of the first half of the pulse. Advantages relative to DPV are that less time is spent at potentials in which adsorption and so on can occur. 

The adsorption of nucleic acids at the electrodes used in electroanalyti-cal chemistry has been mostly investigated with the aid of a.c. polarog-raphy, linear sweep, differential or normal pulse voltammetry, ellipsometry and surface-enhanced Raman scattering spectroscopy. The results of these studies so far obtained have, however, rather qualitative character. Up to recently the samples of nucleic acids which would contain only identical and well defined molecules have not been available in the quantities sufficient for adsorption studies. The use of oligonucleotides or plasmid DNAs appears to be a way to interpret the adsorption analysis of nucleic acids more accurately. 

The quasi-reversihle electroreduction processes of Zn(II) in the absence and in the presence of Ai,Ai -dimethylthiourea (DMTU) were quantitatively compared by Sanecld [91], It has been shown that in the presence of DMTU enhanced response of cyclic voltammetry and normal pulse polarography was complex and could be resolved into its regular reduction part and a part caused by the catalytic influence of adsorption of organic substance. 

Distinguish between (a) voltammetry and amperometry, (b) linear-scan voltammetry and pulse voltammetry, (c) differential-pulse voltammetry and square-wave voltammetry, (d) an RDE and a ring-disk electrode, (e) faradaic impedance and double-layer capacitance, (f) a limiting current and a diffusion current, (g) laminar flow and turbulent flow, (h) the standard electrode potential and the half-wave potential for a reversible reaction at a working electrode, (i) normal stripping methods and adsorptive stripping methods. 

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