Voltammetry stripping voltammetric methods

Brugmann et al. [680] compared three methods for the determination of copper, cadmium, lead, nickel, and zinc in North Sea and northeast Atlantic waters. Two methods consisted of atomic absorption spectroscopy but with preconcentration using either freon or methyl isobutyl ketone, and anodic stripping voltammetry was used for cadmium, copper, and lead only. Inexplicable discrepancies were found in almost all cases. The exceptions were the cadmium results by the two atomic absorption spectrometric methods, and the lead results from the freon with atomic absorption spectrometry and anodic scanning voltammetric methods. 

Anodic (or cathodic) stripping voltammetric (SV) techniques can be used to measure traces of metal in the environment. These methods are very sensitive and their precision is in the order of l to 2%. Stripping voltammetry is carried out in two stages. 

Stripping voltammetry has also been applied to the quantitation of the drug in formulations. A sensitive and precise method using square-wave adsorptive stripping voltammetry has been developed for the determination of sulpha-quinoxaline in veterinary formulations [157]. The differential pulse adsorptive stripping voltammetric determination of midazolam in injectable formulations as a method for quality control has been demonstrated [158]. 

Part IV is devoted to electrochemical methods. After an introduction to electrochemistry in Chapter 18, Chapter 19 describes the many uses of electrode potentials. Oxidation/reduction titrations are the subject of Chapter 20, while Chapter 21 presents the use of potentiometric methods to obtain concentrations of molecular and ionic species. Chapter 22 considers the bulk electrolytic methods of electrogravimetry and coulometry, while Chapter 23 discusses voltammetric methods including linear sweep and cyclic voltammetry, anodic stripping voltammetry, and polarography. 

The example given on Figure 20.12 corresponds to anodic voltammetric analysis. When combined with the technique of DPP (Section 20.5.2), stripping voltammetry constitutes the most universally applied voltammetric method. Current instruments for which control of all the parameters is established, allow reproducible conditions and offer an alternative to spectroscopic methods such as atomic emission. 

Pertcchnetatc and Tc(lV) could be more sensitively analyzed in acidic media in the presence of thiocyanate by adsorption stripping voltammetry at the hanging mercury drop electrode using the differential pulse mode. Determinations down to 5-fO " g Te per ml were feasible. An intense eurrent signal at -1.32 V vs SCE was observed if only technetium and thiocyanate were present in the solution. Larger quantities of salts, e.g. chlorides and sulphates, decreased the sensitivity of the method considerably. This, however, could easily be avoided if, after electrodeposition was completed, the primary electrolyte was replaced by a pure solution of dilute acid for the stripping voltammetric step [100]. 

In one sentence state why stripping voltammetry is the most sensitive of all voltammetric methods ... 

Once solid microparticles of a compound have been immobilized on the surface of a suitable electrode, the electrochemical behavior can be studied. When a voltammetric method is used, the starting potential should be carefully set to a value where no reaction is expected. Alternatively, one may start at the open circuit potential, which either has been predetermined or which is measured by the instrument before commencing the scan. In principle, one can record the oxidation and the reduction response of the compound. In many cases it is useful to perform a pre-electrolysis of the compound, either a reduction or oxidation, followed by recording the response of the reverse processes. Thus metal sulfide or metal oxide particles can be converted to metal particles, which are oxidized in a follow-up scan to yield metal-specific signals, very much like in stripping voltammetry of solutions. Practically, there is no limitation with respect to electrochemical measurements that can be carried out with immobilized particles. 

Voltammetric methods are also used to monitor concentrations of heavy metals in effluents of metal plants. This is done by anodic stripping voltammetry where the ions of the heavy metals are reduced and plated simultaneously with mercury ions, added to the sample, on a working electrode. The metals will form amalgam in the thin layer of mercury that is formed on the surface of the working electrode. This sampling step is performed at a potential where all... 

What are the advantages of mercury electrodes for electrochemical measurements What are the advantages of the DME versus a Pt microelectrode for polarography What are the disadvantages of the DME Describe the method of anodic stripping voltammetry. What analytes can it be used to determine Why is stripping voltammetry more sensitive than other voltammetric methods ... 

Aleksandrova and Kletenik [49] proposed voltammetric method for the determination of chloride concentration in different water samples. They use renewable silver working electrode. Both direct anodic voltammetry and cathodic stripping voltammerty could be successfully used in 1 M sulfuric acid. In the case of cathodic stripping method, 3 min per electrolysis step was employed at —0.07 V to obtain silver chloride film at the electrode surface. 

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