Polarographic/ voltammetric analysis

Plato, J.B. Renaissance in polarographic and voltammetric analysis. Anal. Chem. 1972, 44, 75a-85a. 

Electrochemistry is the relationship between electrical properties and chemical substances in reactions. In its application to analytical chemistry, this generally involves the measurement of some electrical property under conditions which, directly or indirectly, allow an association between the magnitude of the property measured and the concentration of some particular chemical species. Such measurements are nearly always made in solution environments. The electrical properties that are most commonly measured are potential or voltage, current, resistance or conductance, or combinations of these. In some instances the electrical property may be a function of time, whereupon time may also be a variable to be measured. Capacitance is a property which, although not usually measured, has influence in polarographic or voltammetric analysis and requires consideration. 

The apparatus for voltammetric analysis consists of a suitable cell, electrodes, a potentiostat or polarograph, and a system for removing oxygen from the solution. 

Voltammetric analysis at solid electrodes usually involves slower scan rates, typically 5-10 minutes per volt. In addition the solution is often stirred. Both of these factors lessen the depletion effect and the peak in the.current potential curve is much less pronounced and the signal is more wave like (Fig. 2.7c). The precise shape depends on the scan and stirring rates. With a fast enough stirring rate the conventional dc polarographic wave is attained. 

Stripping voltammetry is an important, but limited technique, which uses a pre-concentration step to enhance the sensitivity of the voltammetric analysis step. This pre-concentration step is electrochemical using the same instrumentation as the subsequent voltammetric analysis. The simplest polarographic equipment can be used to obtain the highest sensitivity which depends on the length of the pre-concentration step as well as on the sensitivity of the voltammetric stripping step. Since the pre-concentration step requires the production of an insoluble product which can be reproducibly stripped from the electrode surface in the determination step, the use of stripping voltammetry is limited to a few analytes, eg transition metal ions, halides and pseudo-halides. 

I. Polarographic, Voltammetric and Hybrid Techniques (HPLC-EC) Applied in Modern Environmental Analysis... 

Fojta M (2002) Electrochemical sensors for DNA interactions and damage. Electroanalysis 14 1449-1463. Palecek E (1983) Modern polarographic (voltammetric) techniques in biochemistry and molecular biology. II. Analysis of macromolecules. In Milazzo G (ed.) Topics in Bioelectrochemistry and Bioenergetics, vol. 5, pp. 65-151. Chichester WUey. 

Voltammetry and DD. It is evident that DD processes are analogous to voltammetric analysis, first of all to stripping voltammetry. Such similarity strongly facilitated the development of theory, methodology and instrumentation of the DD method. For example, construction of the stoichiograph resembles that of J. Heyrovsky polarograph. Nevertheless, voltammetry can determine only the substances that are capable of redox transformations and only in a relatively narrow range of the indicator electrode polarization, whereas the DD... 

Zuman P, Somer G (2000) Polarographic and voltammetric behavior of selenous acid and its use in analysis. Talanta 51 645-665... 

Many handbooks like the CRC Handbook of Chemistry and Physics provide, on behalf of electrochemistry investigation, values of standard reduction potentials, listed either in alphabetical order and/or in potential order. These must be considered as potentials of completely reversible redox systems. In current analytical practice one is interested in half-wave potentials of voltammetric, mostly polarographic analysis in various specific media, also in the case of irreversible systems. Apart from data such as those recently provided by Rach and Seiler (Spurenanalyse mit Polarographischen und Voltammetrischen Methoden, Hiithig, Heidelberg, 1984), these half-wave potentials are given in the following table (Application Note N-l, EG G Princeton Applied Research, Princeton, NJ, 1980). 

Other frequently used methods for determining fluoride include ion and gas chromatography [150,204,205] and aluminium monofluoride (AIF) molecular absorption spectrometry [206,207]. Less frequently employed methods include enzymatic [208], catalytic [209], polarographic [210] and voltammetric methods [211], helium microwave-induced [212] or inductively coupled plasma atomic emission spectrometry [213], electrothermal atomic absorption spectrometry [214], inductively coupled plasma-mass spectrometry [215], radioactivation [216], proton-induced gamma emission [217], near-infrared spectroscopy [218] and neutron activation analysis [219]. 

Differential pulse voltammetric and polarographic methods described in this section represent a significant enhancement of the available instrumental analysis capabilities for the quantitative speciation of sulfide, thiosulfate, sulfite and of heteroaromatic sulfur moieties in coal conversion process streams and products. 

However, their careful analysis also showed that most of the dianions were not stable in the polarographic or voltammetric time scale, and even less so after bulk electrolysis, and underwent follow-up reactions with water or other electrophilic impurities, details of which are discussed in Sec. III.B. 

For the determination of tin(ll) in kits an EG 8c G polarographic analyzer (model 384) with a static mercury drop electrode (model 303) and a cabinet reference electrode was used. Model 384 is a microprocessor-based polarographic analyzer with built-in floppy disk memory to store and recall analytical curves. By controlling each step of the analysis, the microprocessor automates polarographic and voltammetric measurements. All experimental parameters may be chosen by the operator. Concentrations are computed automatically aud recorded iu the rauge from 0.001 ppb to 9999 ppm. 

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