Polarographic techniques

Polarographic techniques have been used by Sturm and Hans to demonstrate that certain amino-thiadiazoles and -benzthiazoles exist in the amino form (cf. also references 62, 63). This method, which involves comparison of the polarographic rdeuction potentials of the potentially tautomeric substance with those of alkylated reference compounds, has not been applied often, but may well prove to be a means to obtain qualitative information quickly. There is a possibility that the method can be modified to yield quantitative data. ... 

The method, as so far developed, is limited by the condition that the hydration-dehydration reaction must proceed at a rate that is slow compared with the time needed to obtain a polarogram. In principle, the method is capable of much wider application to covalent-hydration studies if use is made of oscillographic polarographic techniques or of chronopotentiometry. These refinements are currently being investigated. 

The development and the very widespread use of the polarographic technique to record i-E curves and the more recent designing of electronic devices known as potentiostats which automatically control the potential of the working electrode at a pre-set value has led to many examples in the literature of organic electrode reactions whose products depend on the potential. Some examples are cited below ... 

Beyond specific polarographic techniques variations of these methods have been developed aiming at simplified and fast evaluation using modified measurement procedures and data processing. Oldham and... 

Parry have described procedures to determine the kinetic parameters of totally irreversible electrode processes using various polarographic techniques [6801d]. (Data obtained with these methods are collectively labelled POL.)... 

In the context of environmental chemistry, various polarographic techniques have been successfully used to measure elemental sulfur and sulfide (H2S and HS ) concentrations in a variety of media, down to nanomolar concentrations. 

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. 

Meites, L. Polarographic techniques. 2nd edit.,p. 96ff. New York J. Wiley Sons 1965. 

The reduction of zinc ions at d.m.e. has widely been studied and the reaction has been reported to be quasi-reversible.94 Van Der Pol and co-workers54 studied this reaction by the faradaic rectification polarographic technique using high-frequency modulated signals. The kinetic parameters have been evaluated by the... 

Polarographic studies of organic compounds are very complicated. Many of the compounds behave as surfactants, most of them exhibit multiple-electron charge transfer, and very few are soluble in water. The measurement of the capacitance of the double layer, the cell resistance, and the impedance at the electrode/solution interface presents many difficulties. To examine the versatility of the FR polarographic technique, a few simple water-soluble compounds have been chosen for the study. The results obtained are somewhat exciting because the FR polarographic studies not only help in the elucidation of the mechanism of the reaction in different stages but also enable the determination of kinetic parameters for each step of reduction. 

The reduction of vanillin has been studied by the FR polarographic technique.107 The FR summit peaks are conspicuous up to 200-250 Hz at all pH s. With an increase in pH, the FR summit peak potential tends to be more cathodic. The FR wave is invariably obtained on the negative side of the abscissa, indicating that a is less than 0.5. The FR polarograms at pH 10.5 are shown in Fig. 31. 

L. Meites and T. Meites, Polarographic Techniques, Interscience, New York, 1955, p. 303. 

This is a modification of the polarographic technique whereby extremely low levels of certain metals are first pre-concentrated at a stationary... 

The kinetics and mechanism of the ketone-bisulfite addition were studied by the use of the polarographic technique (Rao Salunke, Reaction Kinetics and Catalysis Letters 26 273, 1984).The specific rate was found to depend on pH. For an equimolar solution of bisulfite and acetone in a deaerated solution of potassium hydrogen phthalate buffer containing potassium iodide as the... 

The realization that current sampling on a step pulse can increase the detection sensitivity by increasing the faradaic/charging ratio is the basis for the development of various pulse voltammetric (or polarographic) techniques. Also, the pulses can be applied when it is necessary and can reduce the effect of diffusion on the analyte. Figure 18b. 11 shows the waveform and response for three commonly used pulse voltammetric techniques normal pulse voltammetry (NPY), differential pulse voltammetry (DPV), and square-wave voltammetry (SWV). 

Meites, L. Polarographic Techniques, 2nd Edition, Interscience Publishers, New York (1965). 

In classical polarographic techniques, a dropping mercury electrode is used. This is a complex device in which continuously produced small droplets of mercury are used as the active electrode in order to prevent poisoning of the electrode and to provide constant conditions throughout the analysis. For many applications, specifically designed electrodes are available which are simpler to use. 

The polarographic technique can be used to measure the rates of rapid reactions. Because an internal process is examined the problem of mixing is avoided, as it is in the relaxation and other non-flow methods. The rate of diffusion of a species (which can be oxidized or reduced) to an electrode surface competes with the rate of a chemical reaction of that species, for example... 

For example, (a) Kolthoff, I.M., Lin-gane, J. J. Polarography, 2nd edn., Interscience Publishers, New York, 1952 (b) Meites, L. Polarographic Techniques, 2nd ed., Interscience Publishers, New York, 1965 (c) Heyrovsky, J., Kuta, J. Principles of Polarography, Academic Press, New York, 1966 (d) Bond, A. M. Modem Polarographic Methods in Analytical Chemistry, Marcel Dekker, New York, 1980 ... 

Studies using a differential-pulse polarographic technique, which is recommended in place of classical direct current polarography, yielded the following results. For... 

Other structures which have been confirmed polarographically are those of 5-imino-[benzthiazolo-(2,3-6)]-l,2,4-thiadiazoline (357) and N-thiocyanato-5-imino-[benzthiazolo-(2,3- )]-l,2,4-thiadiazoline (358).180 A polarographic technique has been employed165 for demonstrating the absence of acidic hydrogen in 2,4-dimethyl-l,2,4-thiadiazolidine-3,5-dithione. 

Explain what is done in anodic stripping voltammetry. Why is stripping the most sensitive polarographic technique ... 

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