Voltametric analysis

Cyclic voltametric analysis has been utilized to determine material properties of this class of heterocyclic compounds. All the DTPs 23 <2003JOC2921 > exhibited a well-defined irreversible oxidation presumably corresponding to the formation of the radical cation. When scanned to higher positive potentials, it resulted in two consecutive broad oxidations for most of the DTPs. The second oxidation is quite weak, followed by a more intense and well-defined third oxidation. Coupling of thiophene radical cation is usually rapid (r <10-5 s) <1995SM(75)95>. These additional broad waves most likely correspond to the oxidation of coupled products rather than further DTP oxidations. The electrochemical data of the DTP S 23 are given in the Table 10. 

The determination of hydroperoxide number is significant because of the adverse effect of hydroperoxides on certain elastomers in the fuel systems. This method (ASTM D-6447) measures the same peroxide species,primarily the hydroperoxides in aviation fuels. This test method does not use the ozone-depleting substance l,l,2-trichloro-l,2,2-trifluoroethane (ASTM D-3703) and is applicable to any water-insoluble, organic fluid, particularly diesel fuels, gasoline, and kerosene. In this method, a quantity of sample is contacted with aqueous potassium iodide (KI) solution in the presence of acid.The hydroperoxides present are reduced by potassium iodide,liberating an equivalent amount of iodine, which is quantified by voltametric analysis. 

These carbon fiber electrodes can also be used for voltametric analysis of transmitters in vivo, but the electrodes must not be spark-etched as they become electrically noisy, instead they can be plated with silver [52]. 

Thomas, F.G., Henze, G., 2001. Introduction to Voltametric Analysis Theory and Practice. Cisco... 

The approved variations [14] in the Karl Fischer method include volumetric titration methods to either a visual (excess iodine or addition of an indicator) or volta-metric endpoint detection method. The visual or voltametric endpoint methods usually require 30-40 mg of sample for analysis for freeze-dried biological products containing from 1.0% to 3.0% residual moisture. Coulometric Karl Fischer instruments generate the iodine from potassium iodide for water titration at the electrodes. Only 10-20 mg of freeze-dried sample is required for accurate analysis. 

Diaz-Cruz, M S., Mendieta, J., Tauler, R., Esteban, M., 1997. Cadmium-binding properties of glutathione a chemometrical analysis of voltametric data. J. Inorg. Biochem. 66, 1997. 

Voltametric techniques are based on the relation between current and voltage in an electrochemical process. Among them, anodic stripping voltampe-rometry permits metallic species determination with detection limits of parts per billion or lower. The equipment used with these techniques is much more inexpensive than that used with spectroscopic techniques that are also used in trace analysis. 

In food analysis, the most common electrochemical methods are potentiometric and voltametric. 

Electrochemical detection is very sensitive for the compounds that can be oxidized or reduced at low-voltage potentials. Therefore, it could also be applied in the HPLC analysis of phenolic acids that are present in natural samples at very low concentrations. With the recent advances in electrochemical detection, multi-electrode array detection is becoming a powerful tool for detecting phenolic acids and flavonoids in a wide range of samples. The multi-channel coulometric detection system may serve as a highly sensitive way for the overall characterization of antioxidants the coulometric efficiency of each element of the array allows a complete voltametric resolution of analytes as a function of their reaction (redox) potential. Some peaks may be resolved by the detector, even if they are unresolved when they leave the HPLC column. "... 

A single ashing procedure is often insufficient for the complete decomposition of a complex matrix, leading some authors to recommend a combination of two or more techniques. One example will suffice to illustrate the principle pressure ashing followed by UV photolysis. Thus, it has been shown that analysis of olive leaves for heavy metals by voltametric methods leads to distorted results after pressure digestion alone. Reliable data can be obtained only by supple-menting the digestion with UV irradiation to ensure adequate decomposition of the matrix [41]. 

In a paper by Wasterlain et al. (2011) a new instrument developed in-lab is proposed to satisfy the requirements of electrochemical impedance studies to be led on large fuel cell plants made of numerous individual cells. Moreover, new voltammetry protocols dedicated to PEMFC stack analysis are described. They enable, for example, the study of membrane permeability and loss of platinum activity inside complete PEMFC assemblies. In the first part, a new electrochemical impedance spectrometer that makes testing large FC stacks possible has been presented. To validate this acquisition system and to demonstrate some of its capabilities, some experiments were conducted on a 20-cell PEMFC stack. In the second part, voltanunetry experiments were conducted on short FC stacks with a commercial potentiostat. The fuel crossover phenomenon in a three-cell PEMFC stack was analyzed using the linear sweep voltametric (LSV) method. The crossover rates were determined for each individual cell inside the complete assembly and for the entire stack as well. 

Bruland KW, Coale KH, Mart L (1985) Analysis of seawater for dissolved cadmium, copper, and lead An intercomparison of voltametric and atomic absorption methods. Mar Chem 17 285-3(X). 

A molecularly imprinted polymer of bis(2,2 -bithienyl)methanes has recently been reported for the selective differential pulse voltametric (DPV), piezoelectric micro-gravimetric (PM) and capacitive impedometric (Cl) determination of adrenaline. To this end, protonated adrenaline was used as the template in the preparation of a thin film of an MIP, which was coating the electrode. The device was later used for the analysis of the template, with detection limits of 2 nM, 0.5 pM and 1.5 pM for the DPV, PM, and Cl respectively [357]. 

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