Reactions of superoxide anion radical with antioxidants and their use in voltammetry

Kinetic parameters were calculated for the electrochemical reduction of oxygen at a glassy-carbon electrode with the generation of superoxide radical anions in a 0.05 M solution of (C₂H₅)₄NI in dimethylformamide in the presence of fat-soluble antioxidants, retinol and -tocopherol. A procedure based on the protonation of the radical anion with antioxidant molecules is proposed for the voltammetric determination of antioxidants to determine milligram amounts of retinol and -tocopherol in model solutions (RSD = 1–2%). The calibration graphs for retinol and -tocopherol are linear in the concentration ranges 9.7 × 10^–5–2.3 × 10^–3 and 6.2 × 10^–4–3.1 × 10^–3 M, respectively. The detection limits for retinol and -tocopherol are 4.8 × 10^–5 and 4.1 × 10 ^–4 M, respectively. The procedure was applied to the determination of the active component (retinol and -tocopherol) in pharmaceuticals.Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 1, 2005, pp. 56–59.Original Russian Text Copyright © 2005 by Ziyatdinova, Gilmetdinova, Budnikov.     

Electrochemical Determination of Lipoic Acid

Procedures for determining lipoic acid by voltammetry and coulometric titration with electrogenerated halogens using the biamperometric indication of the titration end-point were developed. Possible mechanisms of lipoic acid oxidation with electrogenerated halogens are discussed. Microgram amounts of lipoic acid were determined in model solutions with an RSD of 1–2%. The analytical range of lipoic acid found by voltammetry at a glassy-carbon electrode lies between 1.15 × 10^–5 and 1.73 × 10^–4 M. The detection limit for lipoic acid is 5.75 × 10^–6 M.     

Galvanostatic coulometry in the analysis of natural polyphenols and its use in pharmacy

Stoichometric coefficients are found for the reactions of electrogenerated halogens and hexacyanoferrate(III) ions with natural polyphenols, namely, rutin, quercetin, and dihydroquercetin, and also with ascorbic acid. The number of electrons participating in the reactions with hexacyanoferrate(III) matches the number of hydroxyl groups in the analyte molecules, which is reflected by the respective reaction schemes. In the determination of the specified compounds in model solutions, the value of RSD was 0.4–6%. A procedure for the direct quantification of polyphenols in pharmaceuticals by the reaction with hexacyanoferrate is proposed; it is proved applicable for the quality control of medications; RSD does not exceed 7%. The variation of titrants, i.e., iodine and hexacyanoferrate, makes possible the determination of phenols in the presence of ascorbic acid.     

Biosensor with Protective Membrane for the Detection of DNA Damage and Antioxidant Properties of Fruit Juices

With the purpose to prepare a DNA biosensor protected with an outer‐sphere membrane against high molecular weight interferences, a carbon film electrode was layer‐by‐layer modified with dsDNA and chitosan. Using cyclic and square‐wave voltammetry and impedance spectroscopy, the oxidative damage of DNA by the hydroxyl and superoxide anion radicals was detected which consists of opening of the helix structure followed by deep DNA chain degradation. The biosensor has been applied to the detection of the antioxidant effect of apple and orange juices. The investigation of the novel biosensor with a protective membrane represents a significant contribution to the field of DNA biosensors utilization.     

High quality beam shaping by square soft-edge diaphragm combined with liquid crystal spatial light modulator

<正>The square soft-edge diaphragm with round angle is designed by Matlab,and is sent to a liquid crystal spatial light modulator by the computer.In order to obtain precompensation for the following laser system, local diaphragm transmission can be adjusted by feedback signals of surface-channel charge-coupled device (SCCD).This method can reduce the diffraction effect and realize no modulation,high stability,high homogeneity,and large scale laser beam.Several parameters of soft-edge diaphragms which affect the laser beam quality are studied systematically,and the optimized values are obtained.The method can avoid the serious modulation of hard edges and provide soft-edge diaphragms of different shapes in a fast and convenient way for the large scale laser beam system.     

Voltammetric Determination of Tartrazine on an Electrode Modified with Cerium Dioxide Nanoparticles and Cetyltriphenylphosphonium Bromide

Journal of Analytical Chemistry - We created glassy carbon electrodes (GCEs) modified with CeO2 nanoparticles and various surfactants and determined the voltammetric characteristics of tartrazine...     

Iron(III) salicylate complexes in surfactant solutions

Electron spectroscopy combined with the computer simulation of experimental data is employed to study the influence of different surfactants on the equilibria involved in the formation processes of bis- and tris(ligand) complexes of iron with salicylic acid (H₂L). It is established that the formation of tris(ligand) complexes FeL₃ is stimulated by both micelles and premicellar aggregates of cationic surfactants in the presence of excess ligand and only by premicellar aggregates at the deficiency of the ligand. The replacement of pyridinium head group by trimethylammonium group decreases the effect, while the application of cationic surfactants with hexadecyl radicals reduces the solubility of the complexes in water.     

The application of coulometry for total antioxidant capacity determination of human blood

New coulometric method for estimation of blood and plasma total antioxidant capacity (TAC) based on using electrogenerated bromine was proposed. TAC of blood from patients with chronic renal disease undergoing long-term hemodialysis was investigated. Statistical significant changes in TAC level of venous and arterial blood were found. Catalase activity and low density lipoproteins (LDL) concentrations were determined. Linear correlation between TAC and parameters mentioned was found. Contribution from some individual antioxidants was investigated. The developed method for TAC assay is expressive, simple, stable and reliable, and successfully could be used for TAC determination of some biological fluids. This method could be applied in clinic for estimation of blood TAC from patients.     

Chronoamperometric evaluation of the antioxidant capacity of tea on a polyquercetin-modified electrode

It was established that the components of tea are oxidized on a glassy carbon electrode modified with carbon nanotubes and electropolymerized quercetin in a phosphate buffer solution (pH 7.0) as a supporting electrolyte under conditions of differential pulse voltammetry. The oxidation potentials of the individual phenolic antioxidants of tea (gallic acid, rutin, quercetin, catechin, epigallocatechin gallate, and tannin) on the modified electrode were found. A method for the chronoamperometric determination of the antioxidant capacity (AOC) of tea was developed based on the oxidation of tea antioxidants at a potential of 0.20 V. The AOC of tea was evaluated using а difference between the oxidation currents of the analyte and a supporting electrolyte after 50 s of electrolysis in terms of gallic acid. The analytical range of gallic acid was 0.25?750 μM with a detection limit of 0.063 μM. Positive correlations of the AOC with antioxidant activity in a reaction with 2,2-diphenyl-1-picrylhydrazyl and the total phenolic content were found (r = 0.700 and 0.647 at r _crit = 0.396, respectively).