Dragan A. Marković

Antioxidative capabilities of some organic acids and their co-pigments with malvin: Part II

Abstract Antioxidative properties of ferulic, sinapic, and tannic acids, and their co-pigment with an anthocyan molecule, malvin, were electrochemically observed by cyclic voltammetry. The values of oxidation potentials were used as a quantitative parameter in determining oxidation capabilities of the compounds. These values imply the following sequence of increasing antioxidative effect: ferulic acid

Assessment of Air Quality in an Urban Area of Belgrade, Serbia

Mirjana Tasi a, Slavica Rajsi a, Milica Tomasevi a, Zoran Miji a, Mira Ani i a, Velibor Novakovi a, Dragan M. Markovi a, Dragan A. Markovi b, Lazar Lazi c, Mirjana Radenkovi d and Jasminka Joksi d aInstitute of Physics, Belgrade, Serbia bFaculty of Applied Ecology, Singidunum University, Belgrade, Serbia cInstitute of Meteorology, Faculty of Physics, Belgrade, Serbia dInstitute of Nuclear Science Vin a, Belgrade, Serbia

Association Forms Of Heavy Metals In Fly Ash From Power Plants

During coal combustion, the organic component becomes oxidised, while inorganic components mostly remain in the ash. All natural elements were found in coal, except some very rare ones, like polonium, francium, astatine, etc. (Finkelman 1993). The variability of inorganic constituents is influenced by biological, hydrological and geochemical factors and their association forms govern their behaviour and their technological and environmental impact. Emission and deposition of coal ash represent major environmental problems, due to the large amount of ash obtained. The environmental impact of ash has at least two aspects: a) emission and deposition of enormous amounts of ash particles, polluting air, water and soil; b) leaching of microelements (including toxic metals), but also major cations and anions from ash by atmospheric and surface waters.

The polarographic behavior of metal ions in molten LiNO3−KNO3 eutectic in presence of complexon III

Summary The possibility of using complexon III as a complexing substance in the polarography of salt metls (LiNO 3 −KNO 3 eutectic) has been investigated. Complexon III was found to form complexes with Cd, Pb, Ni and Zn ions in the ratios 1:2 for Cd and Pb, 2:1 for Ni and 1:1 for Zn. Cadmium and lead complexes can be reduced at the DME with E 1/2 =−0.70 V for the cadmium complex and E 1/2 =−0.59 V for the lead complex ( vs. a calomel reference electrode). Diffusion coefficients D =1.5×10 −6 cm 2 s −1 and D =2.5×10 −6 cm 2 s −1 were found for non-complexed cadmium and lead ions, respectively. Complexes of cadmium and lead with complexon III gave values of D =3.0×10 −7 cm 2 s −1 and D =3.7×10 −7 cm 2 s −1 , respectively, at 170°C. The activation energy of the complexed and non-complexed Cd ion diffusion current Q =4.50 kcal mol −1 and the heterogenous electrode process rate constants k e 0 =2.5×10 −6 cm s −1 for the complexed ion have been determined.

Polarographic behaviour and determination of 1-(4'-bromophenyl)-3,3-dimethyltriazene

Abstract A study was made of the polarographic behaviour of the genotoxic substance 1-(4′-bromopheyl)-3,3-dimethlytriazene and optimum conditions were found for its determination by tast polarography and differential-pulse polarography at a static mercury drop electrode in the concentration range 1 × 10 −4 −1 × 10 −7 mol dm −3 . The results indicate that the method can be used at pH between 4.5 and6.0 for the identification and determination of the investigated substance, which is protonated without decomposition in this pH range. It was established that for the reduction of the NN group four electrons are required and the resulting products are 4-bromoaniline and dimethylhydrazine.

Adsorptive stripping voltammetric determination of 1-(4′-bromophenyl)-3,3-dimethyltriazene

The optimum conditions were established for the determination of the genotoxic substance 1-(4′-bromophenyl)-3,3-dimethyltriazene by differential-pulse voltammetry at a hanging mercury drop electrode in the concentration range 1 × 10−4 to 1 × 10−7 mol dm−3. The sensitivity of the determination can be improved through adsorptive accumulation of the investigated substance on the surface of the hanging mercury drop electrode: differential pulse adsorptive stripping voltammetry can be used in the concentration range 1 × 10−7 to 2 × 10−10 mol dm−3. The relative standard deviation (for ten determinations at 2 × 10−10 mol dm−3) was 7.5%.

Electrochemical behaviour of rosmanol 9-ethyl ether, a diterpene lactone antioxidant isolated from sage

The electrochemical behaviour and mechanism of the redox process of the natural antioxidant rosmanol 9-ethyl ether, isolated fromSaliva officinalis L., were studied. The cyclic voltammograms of rosmanol 9-ethyl ether (R9EE), at characteristic pH values, and the electrochemical parameters for all investigated pH values were measured. Three characteristic pH regions, each with different behaviour of R9EE, were identified. In regions of pH < 4 and pH > 5 only one anodic peak appeared, whereas in the solutions of pH 4–5 two anodic peaks could be noted. The overall oxidation mechanism at pH < 4 is an e.H.e.H. oxidation mechanism, which as a final product gives a quinonic molecule. The influence of pH on the second oxidation peak potential tends towards zero in accordance with the preceding dissociation of the one of phenolic groups, thus suggesting an e.e.H. mechanism at pH > 5. This means that at the pH values expected in plant cells, R9EE has an unexpected structure, making this substance a potent antioxidant. Electrochemical and spectrophotometric measurements enabled us to establish an extremely low pKa value (4.35) for R9EE.

Metal complexes with chloramphenicol: Part I. Polarographic investigation of copper-chloramphenicol complexes

Abstract Polarographic investigations of copper-chloramphenicol (Hf) complex were performed in 1 M NaCl which was used as the supporting electrolyte, at pH values from 11 to 13. Amperometric titration method was used to determine the composition of the complex compound. The molar ratio Cu to Hf varies with pH value of solution but not with relative KOH to Hf ratio. At pH values 12–12.5 amperometric curves indicate formation of complex compound with Cu to Hf molar ratio equal 1:2. It was found that a two-electron irreversible process takes place on the DME. The value of diffusion coefficient of the reducible species D=9.25×10−7 cm2 s−2 was found.

The influence of chemical oxidation and polishing on the surface and characteristics of a glassy carbon electrode

Abstract The effects of chemical oxidation and polishing on the condition of a glassy carbon surface have been investigated. The electrochemical characteristics of the laboratory-made glassy carbon electrode were examined and found to be satisfactory. Chemical oxidation with chromic acid led to a considerable decrease in the difference between the anodic and cathodic current-potential peaks (ΔEp), indicating increased reversibility of the electrode processes. Glassy carbon samples were treated in the same manner as the electrode by polishing and/or chemical oxidation with chromic acid, and the topography of the treated surfaces was examined by SEM. It was found that mechanical damage caused by abrasives plays a significant role in surface destruction by chromic acid.

The role and importance of ozone for atmospheric chemistry and methods for measuring its concentration

Depending on where ozone resides, it can protect or harm life on Earth. The thin layer of ozone that surrounds Earth acts as a shield protecting the planet from irradiation by UV light. When it is close to the planets surface, ozone is a powerful photochemical oxidant that damage, icons frescos, museum exhibits, rubber, plastic and all plant and animal life. Besides the basic properties of some methods for determining the ozone concentration in working and living conditions, this paper presents a detailed description of the electrochemical method. The basic properties of the electrochemical method are used in the construction of mobile equipment for determining the sum of oxidants in the atmosphere. The equipment was used for testing the determination of the ozone concentration in working rooms, where the concentration was at a high level and caused by UV radiation or electrostatic discharge. According to the obtained results, it can be concluded that this equipment for determining the ozone concentration in the atmosphere is very powerful and reproducible in measurements.