Polarography anodic voltammetry

Various spectroscopic techniques such as flame photometry, emission spectroscopy, atomic absorption spectrometry, spectrophotometry, flu-orimetry, X-ray fluorescence spectrometry, neutron activation analysis and isotope dilution mass spectrometry have been used for marine analysis of elemental and inorganic components [2]. Polarography, anodic stripping voltammetry and other electrochemical techniques are also useful for the determination of Cd, Cu, Mn, Pb, Zn, etc. in seawater. Electrochemical techniques sometimes provide information on the chemical species in solution. 

Electrochemical methods are preferred for aqueous solutions, such as polarogra-phy, differential pulse polarography, pulse voltammetry, and pulse inverse voltammetry. The anodic (ASV) and cationic (CSV) stripping voltammetry are at present the most sensitive analytical methods for copper determination with a detection limit of 5 ng (Donat et al. 1994). 

Carbon paste electrodes have acquired greater importance in the field of electrochemistry due to their low residual current and noise and because they are very economic and easy to prepare and replace. These electrodes have a wide range of anodic and cathodic applications. Electrode surface modification is a field of great importance in the modem electrochemistry especially due to the various applications. Some electrochemical techniques, such as differential pulse polarography, stripping voltammetry, differential pulse voltammetry and square-wave voltammetry have been widely applied for the determination of pharmaceuticals. 

When either pulse polarography or anodic stripping voltammetry can be used, the selection is often based on the analyte s expected concentration and the desired... 

From the nature of the process described above it has been referred to as stripping polarography , but the term anodic stripping voltammetry is preferred. It is also possible to reverse the polarity of the two electrodes of the cell, thus leading to the technique of cathodic stripping voltammetry. 

Electrochemistry voltammetry, anodic stripping (ASV), cathodic stripping (CSV), polarography, differential pulse polarography (DPP), ion selective electrode (ISE)... 

Stolzberg [143] has reviewed the potential inaccuracies of anodic stripping voltammetry and differential pulse polarography in determining trace metal speciation, and thereby bio-availability and transport properties of trace metals in natural waters. In particular it is stressed that nonuniform distribution of metal-ligand species within the polarographic cell represents another limitation inherent in electrochemical measurement of speciation. Examples relate to the differential pulse polarographic behaviour of cadmium complexes of NTA and EDTA in seawater. 

In polarography, we obtained the half-wave potential E// by analysing the shapes of the polarographic wave. E1/2 is a useful characteristic of the analyte in the same way as E . In cyclic voltammetry, the position o/both peaks (both forward and back in Figure 6.13 cathodic and anodic, respectively, in this example) gives us thermodynamic information. Provided that the couple is fully reversible, in the thermodynamic sense defined in Table 6.3, the two peaks are positioned on either side of the formal electrode potential E of the analyte redox couple, as follows ... 

Stripping is the most sensitive form of voltammetry. In anodic stripping polarography, analyte is concentrated into a single drop of mercury by reduction at a fixed voltage for a fixed time. The potential is then made more positive, and current is measured as analyte is reoxidized. In cyclic voltammetry, a triangular waveform is applied, and cathodic and anodic processes are observed in succession. Microelectrodes fit into small places and their low current allows them to be used in resistive, nonaqueous media. Their low capacitance... 

Cyclic voltammetric methods, or other related techniques such as differential pulse polarography and AC voltammetry,3 provided a convenient method for the estimation of equilibrium constants for disproportionation or its converse, comproportionation. In this respect, the experimentally measured quantity of interest in a cyclic voltammetric experiment is E>A, the potential mid-way between the cathodic and anodic peak potentials. For a one-electron process, E,A is related to the thermodynamic standard potential Ea by equation (4).13 In practice, ,/2 = E° is usually a good approximation. 

Bilinski, H., Huston, R. and Stumm, W., 1976. Determination of the stability constants of some hydroxo and carbonate complexes of Pb(II), Cu(II), Cd(ll) and Zn(II) in dilute solutions by anodic stripping voltammetry and differential pulse polarography. Anal. Chim. Acta, 84 157-164. 

Electrochemical methods for arsenic determination were initially based on polarography with a dropping mercury electrode. More recent methods, based on anodic stripping voltammetry (ASV), anodic stripping chronopotentiometry (SC), and CSV, rely almost exclusively on the detection of As(III), since As(V) is detected with difficulty because of its perceived electro-inactivity. 

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). 

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