Polarography dropping-mercury electrode

Drop time in polarography, 597, 608 Dropping mercury electrode 608, 628 Dry ashing 114 Dry box lOl Drying reagents 99 comparative efficiencies of, (T) 99 Drying of precipitates 119 Duboscq colorimeter 656 Duplication method 701... 

Vittori O (1980) Polarographie study of adsorbed tellurium at the hanging and dropping mercury electrodes in 1 M hydrochloric or perchloric acid solutions. Anal Chim Acta 121 315-319... 

In voltammetry as an analytical method based on measurement of the voltage-current curve we can distinguish between techniques with non-stationary and with stationary electrodes. Within the first group the technique at the dropping mercury electrode (dme), the so-called polarography, is by far the most important within the second group it is of particular significance to state whether and when the analyte is stirred. 

The gamma isomer of benzene hexachloride can also be determined by polarography (24, 0). The method is based on the fact that, under the conditions used, the gamma isomer is the only one of the five isomers that is reduced at the dropping mercury electrode. 

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). 

Lopez-Fonseca et al. [11] discussed the theory of reverse pulse polarography and the technique was applied in the determination of penicillamine electrochemically coated on a dropping-mercury electrode. Using long drop times and short pulses, the drug can be determined at levels as low as 50 nM in the presence of Cu(II), and the technique compares well with normal-pulse and differential-pulse polarography. 

Voltammetry is a part of the repertoire of dynamic electrochemical techniques for the study of redox (reduction-oxidation) reactions through current-voltage relationships. Experimentally, the current response (i, the signal) is obtained by the applied voltage (.E, the excitation) in a suitable electrochemical cell. Polarography is a special form of voltammetry where redox reactions are studied with a dropping mercury electrode (DME). Polarography was the first dynamic electrochemical technique developed by J. Heyrovsky in 1922. He was awarded the Nobel Prize in Chemistry for this discovery. 

Polarography is the measurement of the current flowing at a dropping mercury electrode as the potential applied to this electrode is changed. Voltammetry is the measurement of the current flowing at a stationary electrode as the potential applied to this electrode is changed. 

The electrode potential obtained with linear-sweep polarography, for example, at a dropping-mercury electrode (DME), is different again and is called the halfwave potential, 1/2, which is also discussed in Chapter 6. 

Figure 6.6 shows a schematic diagram of the apparatus required as a working electrode for polarography. Such a set-up is almost universally called a dropping mercury electrode (DME), with the mercury drop being immersed in a cell that is essentially the same as that shown in Figure 6.1. 

Figure 6.6 Schematic representation of a typical dropping-mercury electrode (DME) for polarography, where the DME acts as a working electrode in a cell such as that shown in Figure 6.1. The platinum electrode at the top right of the diagram is needed to give an electrical connection. The rate of mercury flow is altered by adjusting by changing the height h.

Dropping mercury electrode (DME) Historically, a popular choice of working electrode in polarography. 

Hanging mercury-drop electrode (HMDE) A commonly employed working electrode in polarography. The HMDE is often preferred to the experimentally simpler dropping mercury electrode (DME) because resultant polarograms do not have a sawtoothed appearance and because accumulation (for stripping purposes) is readily achieved at its static surface. 

Polarography The techniques and methodology of a form of voltammetry in which the working electrode is liquid, elemental mercury, usually employed within a dropping mercury electrode (DME) or a hanging mercury-drop electrode (HMDE). 

The existence of various oxidation states of technetium indicates the possibility of using polarography for its quantitative determination. Polarographic reduction of the pertechnetate ion at a dropping mercury electrode has been studied in different supporting electrolytes . 

For the rapid determination of Tc in a mixture of uranium fission products. Love and Greendale have used the method of amalgam polarography. It consists in a selective reduction of technetium at a dropping mercury electrode at a potential of —1.55 V vs. SCE in a medium of 1 M sodium citrate and 0.1 M NaOH. Under these conditions, technetium is reduced to an oxidation state which is soluble in mercury. The amalgam is removed from the solution of fission fragments and the amount of Tc determined in nitric acid solution of the amalgam by a y count. For Tc the measurement accuracy is within 1 %, and the decontamination factor from other fission products 10 . 

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