Electrochemical analysis polarography

Principles and Characteristics A substantial percentage of chemical analyses are based on electrochemistry, although this is less evident for polymer/additive analysis. In its application to analytical chemistry, electrochemistry involves the measurement of some electrical property in relation to the concentration of a particular chemical species. The electrical properties that are most commonly measured are potential or voltage, current, resistance or conductance charge or capacity, or combinations of these. Often, a material conversion is involved and therefore so are separation processes, which take place when electrons participate on the surface of electrodes, such as in polarography. Electrochemical analysis also comprises currentless methods, such as potentiometry, including the use of ion-selective electrodes. 

B. Breyer and H. H. Bauer, Alternating Current Polarography and Tensammetry, Interscience, New York, 1963 see also Z. Galus, Fundamentals of Electrochemical Analysis, Ellis Horwood, Chichester, 1976, p. 503-504, and H. Jehring, J. Electroanal. Chem., 20 (1969) 33 and 21 (1969) 77. 

Twenty years ago the main applications of electrochemistry were trace-metal analysis (polarography and anodic stripping voltammetry) and selective-ion assay (pH, pNa, pK via potentiometry). A secondary focus was the use of voltammetry to characterize transition-metal coordination complexes (metal-ligand stoichiometry, stability constants, and oxidation-reduction thermodynamics). With the commercial development of (1) low-cost, reliable poten-tiostats (2) pure, inert glassy-carbon electrodes and (3) ultrapure, dry aptotic solvents, molecular characterization via electrochemical methodologies has become accessible to nonspecialists (analogous to carbon-13 NMR and GC/MS). 

DC voltammetry — Voltammetry with an applied DC potential that varies, usually, linearly with time. That is, constant d V/dt without embellishments of the voltage perturbation as applies, for example, in AC voltammetry. See -> polarography, and subentry - DC polarography. Refs. [i] Bond AM (1980) Modern polarographic methods in analytical chemistry. Dekker, New York [ii] Galas Z (1994) Fundamentals of electrochemical analysis, 2nd edn. Ellis Horwood, New York, Polish Scientific Publisher PWN, Warsaw... 

Electrochemical analysis is composed of a vast range of techniques such as potentiometry, polarography, amperometry and coulometry. Selection of the technique best suited to the purpose and of the appropriate working conditions ensure a high degree of sensitivity and selectivity. 

Alternatively, air is passed through 1-pm PTFE membrane and 1% sodium bisulfite solution. The solution is treated with chromotropic and sulfuric acid mixture. The color development due to formaldehyde is measured by a visible spectrophotometer at 580-mn absorbance (NIOSH 1984, Method 3500). In polarography analysis, a Girard-T reagent is used. Formaldehyde forms a derivative that is analyzed by sampled direct current DC polarography (NIOSH 1984, Method 3501). Auel et al. (1987) reported a similar electrochemical analysis of industrial air using an iridium electrode backed by a gas-permeable fluorocarbon-based membrane. 

The analytical method described here is based on the results obtained with dc polaro-graphy and differential pulse polarography at dropping mercury electrode. The detection and determination of the drug metronidazole (I) continues to be of interest, particularly because of its status as a drug of abuse. The nitro group in metronidazole is useful in electrochemical analysis. 

Heyrovsky worked out the theory for the mercury electrode In polarography, an electrochemical analysis method which, after a few improvements, meant that ultra-traces could be analysed In heavy metals for instance. He was awarded the Nobel prize for his work In 1959. 

Mercury has been widely used in electrochemistry, especially as a working electrode due to its unique electrochemical properties. The employment of a mercury electrode as the working electrode is called polarography, which was invented by Professor Jaroslav Heyrovsky in 1922 [1], Prof. Heyrovsky was awarded Nobel Prize in 1959 for the significance polarography has estabhshed in electrochemical analysis. In this entiy, we will introduce different types of mercury drop electrodes, the associated techniques for utilizing mercury electrodes, and the applications of mercury electrodes for the determination of various species. 

Isomers of tocopherols in edible oils were quantified using electrochemical methods polarography (Smith et al., 1941), and differential pulse voltammetry (Galeano et al., 2004 Robledo et al., 2013). A couple of spectrophotometric assays were used to quantify tocopherols copper(II)-neocuproin system (Tiitem et al., 1997). GC-MS analysis reveals the instability at heating of y-tocopherol Ifom com oil. This isoform is converted to a-tocopherol and later degraded when temperature is increased (Sim et al., 2014). 

Pournaghi-Aznar MH, Shemirani F, Pourtork S (1995) Electrochemical behavior of some naturally occurring hydroxy derivatives of 9,10-anthraquinone in chloroform at mercury and glassy carbon electrodes application of AC polarography to the analysis of Rhubarb roots. Talanta 42 677-684. 

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