Analytical & Bioanalytical Electrochemistry
Volume:3 Issue: 6, Dec 2011

A stable modified carbon paste electrode based on the poly (tryptophan) film was prepared by electrochemical polymerization technique using cyclic voltammetry. The properties of the electrodeposited films, during preparation under different conditions and their stability were evaluated. It was found that the current response of DA and AA were greatly enhanced at this poly (tryptophan) modified carbon paste electrode. Moreover, the anodic over-potential of AA was significantly reduced for about 150 mV (vs. SCE) compared with that obtained at bare carbon paste electrode. The modified carbon paste electrode was applied to the study of electrocatalytic oxidation of DA and AA which resolved the overlapping of the anodic peaks of DA and AA in 0.1 mol L-1 acetate buffer solution at pH 6.5. The separation of the oxidation peak potentials for ascorbic acid–dopamine was about 0.277 V. Interference studies showed that the modified electrode exhibits excellent selectivity towards DA and AA.

The analysis of Cu(II) by anodic stripping voltammetry using a Nafion-modified glassy Carbon electrode incorporated with Cu-DPABA complex (DPABA is Methyl 3,5- bis{bis-[(pyridin-2-yl)methyl]amino}methyl)benzoate) (Cu-DPABA–NA/GCE) is described. Cu(II) was accumulated in Hac-NaAc buffer pH=4 at potential of -0.3 V (vs. Ag/AgCl ref. electrode) and then determined with SWASV. Under the optimum conditions the calibration curve was linear in the range 15×10-8–5.6×10-5 mol/L. The detection limit was 8.9 x10 8 mol/L. Different parameters and conditions, such as volume of Nafion and Cu-DPABA, accumulation time and pH value was optimized. A study of the interfering substances was also performed. A significant increase in current was achieved at the modified electrode compared to a bare glassy carbon electrode. For explanation of voltammetric behavior of modified electrode in copper solution, cyclic voltammograms were recorded. The electrode has been used in the direct determination of Cu(II) in water.

Surfactant modified zeolite Y nano cluster was used to characterize its ability as an anion carrier in a PVC membrane electrode. The electrode showed excellent response characteristics to perchlorate anion. The electrode exhibited Nernstian response to ClO4 − anion over a wide concentration range covering the range 1.2×10-6 to 1.5×10-1 M with low detection limit 5.7×10−7 M and a slope of 59.6±0.8 mV per decade of perchlorate concentration. The electrode possess fast response time, reasonable reproducibility, appropriate lifetime and, most importantly, good selectivity toward ClO4 − relative to a variety of other common anions. The electrode response to perchlorate remained constant in the temperature range of 20-45 oC and in the presence of 1.0×10-4–3.2×10-3 M NaNO3. The potentiometric response of the electrodes is independent of the pH of test solution in the pH range of 2.1–10.8. The proposed sensors were used in potentiometric determination of perchlorate ions in river and tap waters.

In the current study, the electrochemical behaviors of 4,4'-oxydianiline and 4,4'- oxydiphenylene bisdiazonium tetrafluoroborate salt on the surface of glassy carbon electrode using voltammetry technique. 1 mM 4,4'-oxydianiline in 100 mM tetrabutylammonium tetrafloroborate (in acetonitrile) has been modified to the electrode surface in 0.0 mV and +1800 mV potential range at 100 mV s-1 scanning rate with 50 cycles. The same solvent has been used for 4,4'-oxydiphenylene bisdiazonium tetrafluoroborate salt. 1 mM prepared, '- oxydiphenylene bisdiazonium tetrafluoroborate salt has been modified to the electrode surface in +100 mV and -1200 mV potential range using 100 mV s-1 scanning rate with 10 cycles. Following the modification and characterization process, the sensitivity of 4,4'-oxydiphenylene bisdiazonium tetrafluoroborate salt modified glassy carbon electrodehas been tested against flavones, 3-hydroxyflavone, quercetin, rutin and naringenin. Based on the sensitivity tests, 4,4'-oxydiphenylene bisdiazonium tetrafluoroborate salt modified glassy carbon electrode can be used in the determination of total antioxidant capacity. The further studies will progress through this way. Cyclic voltammetry technique has been utilized for the modification process. Electrochemical impedance spectroscopy and scanning electron microscopy have been used for the characterization process.

Copolymer resin (8-HQ5-SAOF-IV) synthesized by the condensation of 8-hydroxyquinoline5-sulphonic acid and oxamide with formaldehyde in the presence of acid catalyst, was proved to be selective chelating ion-exchange copolymer for certain metals. The chelating ion-exchange properties of this copolymer were studied for Fe (III), Cu (II), Ni (II), Co (II), Zn (II), Cd (II) and Pb (II) ions in the form of their metal nitrate solutions. A batch equilibrium method was employed in the study of the selectivity of metal ion uptake involved in the measurements of the distribution of a given metal ion between the copolymer sample and a solution containing the metal ion. The study was carried out over a wide pH range, shaking time and in media of various ionic strengths of different electrolytes. The copolymer showed a higher selectivity for Fe (III), Cu (II), and Ni (II) ions than for Co (II), Zn (II), Cd (II) and Pb (II) ions. Distribution ratios (D) of metal ions were found to be increased by increasing pH of the solutions; hence the resin can be used to recover certain metal ions from waste solutions and used for the purpose of purification of waste water and removal of iron from boiler water. The ion-exchange capacity of metal ions has also been determined experimentally and compare with other commercial resins. The morphology of the copolymer was studied by scanning electron microscopy (SEM); showing amorphous nature of the resin therefore can be used as a selective ion-exchanger for certain metal ions.

The polyaniline-ferric oxide (Fe2O3) composites have been prepared for different weight percentage such as 5%, 10%, 15% and 20% of Fe2O3. The polymerization was carried out by in-situ chemical oxidation technique with ammonium persulphate (APS) as an oxidizing agent in aqueous sulphuric acid as dopent under constant stirring at 0-4 oC. The characterization of polymer composites has been carried out by FT-IR, UV-Vis so as to conform polymerization, XRD for elucidating the structure of composites. The morphology of composites was studied by SEM. Temperature dependent D.C. electrical conductivity measurement has been carried by four probe technique in the range of 303-373 K. It has been observed that conductivity of all composites is found to be increasing by increasing temperature. The composites of 5%(PF-1) and 10%(PF-2) has been found to be more while composites 15%(PF-3) and 20%(PF-4) has found to be lower than that of pure PANI over entire temperature range. The enhancement in conductivity of PF-1 and PF-2 composites may be due to uncoiling of polymeric chain due to strong interaction of PANI with Fe2O3 crystallites as suggested by FT-IR and XRD studies. Lowering in conductivity of PF-3 and PF-4 may be due to increasing the content in composition which gradually weakened interaction between PANI and Fe2O3; leads to free PANI Chain coexist in the composites and may be due to the particle blockage in conductive path by additive embedded in PANI matrix.

Free cyanide and its related compounds are the most known contaminants which are released from industrial effluents to the environment; the objective of this study was to evaluate the efficiency electrocoagulation reactor with iron plate in order to find optimum operational conditions for cyanide removal from cyanide-containing effluents. The reactor was tested under different operational conditions of voltage (20, 30, and 40 V), detention time (20, 30, 40, 60, and 90 min), and influent concentration (20, 30 40, and 50 mg/l). Since ferrous ion capability to react with free cyanide and its related compounds are (97%) well established, iron plate was used as electrode in the present study. Additionally, to prevent creating ferric ion and ferric hydroxide precipitates in the reactor which decrease the removal efficiency, bisulfite was applied to hold ferrous ion in the reactor. The optimum operational conditions were obtained after running the reactor for several times. Based on the results, the optimum removal efficiency was obtained at voltage of 40 V, detention time of 90 min, and influent concentration of 50 mg/l. Therefore, this process may be considered as an alternative method for the removal of cyanide from cyanide- containing wastewaters.

A novel composite superionic system, [Cu2HgI4:0.2 AgI]:0.xKBr, (x=0.2, 0.4, 0.6 mol. wt. %), was prepared and [Cu2HgI4:0.2 AgI] composite system used as the host. Electrical conductivity was measured to study the transition behavior at frequencies 100 Hz, 120 Hz, 1 kHz, and 10 kHz in the temperature range 90–170 °C using a GENRAD 1659 RLC Digibridge. Conductivity increased sharply during the β - α phase transition. Upon increasing the dopant-to-host ratio, the conductivity of the superionic system exhibited Arrhenius (thermally activated)-type behavior. X-ray powder diffraction, DSC and DTA were performed to confirm the doping effect and transition in the host. The phase transition temperature decreased with an increase in the dopant concentration. Activation energies in eV for pre- and post-transition phase behavior are also reported. Due to an interaction between [Cu2HgI4:0.2 AgI] and KBr, the addition of the dopant KBr shifted the phase transition of the host, [Cu2HgI4:0.2 AgI].