Hailemichael Alemu

Amperometric Determination of Hydrogen Peroxide With a ManganeseDioxide-modified Carbon Paste Electrode Using Flow InjectionAnalysis

A carbon paste electrode bulk modified with MnO 2 was investigated as an amperometric detector for hydrogen peroxide in flow injection analysis (FIA). With an operating potential of +0.46 V versus Ag/AgCl, H 2 O 2 produces catalytic oxidation currents which can be exploited for quantitative determinations. Factors influencing the analytical performance of the electrode, such as paste composition and pH, were studied both for batch voltammetry and for FIA. For the flow system the influence of the injection volume and flow rate were examined. The amperometric signals are linearly proportional to H 2 O 2 concentrations in the range 0.5–350 mg l - 1 , showing a detection limit (three times the signal-to-noise ratio) of 45 µg l - 1 .

(Bio)sensors based on manganese dioxide-modified carbon substrates: retrospections, further improvements and applications

An overview is presented which summarizes our accomplishment in the development of sensors and biosensors based on heterogenous carbon electrodes modified with manganese dioxide. Brief account of each sensor and biosensor has been given and example of real sample applications provided where appropriate.

Differential Pulse Anodic Stripping Voltammetric Determination of Lead(II) with N-p-Chlorophenylcinnamo- hydroxamic Acid Modified Carbon Paste Electrode

A sensitive and selective method for the determination of lead(II) with N-p-chlorophenylcinnamohydroxamic acid modified carbon paste electrode has been developed. The lead(II) is accumulated on the electrode surface by the formation of the complex in an open circuit, and the resulting surface is characterized by medium exchange, electrochemical reduction, and differential pulse anodic stripping voltammetry. The electrochemical response was evaluated with respect to carbon paste composition, pH and concentration of accumulating and stripping solutions, preconcentration time, lead(II) concentration, and other variables. Two linear ranges were obtained in the concentration ranges 1.00610 ˇ6 ‐2.40610 ˇ5 M Pb(II) with 2 min preconcentration time and 2.00610 ˇ8 ‐1.00610 ˇ6 M Pb(II) with 6 min preconcentration time. The detection limit was found to be 1.00610 ˇ8 M with 6 min preconcentration time. For six preconcentration=determination=renewal cycles, the differential pulse voltammetric response was reproduced with 5.3 % and 4.9 % relative standard deviations at 4610 ˇ6 M and 8610 ˇ8 M Pb(II), respectively. Rapid and convenient renewal allows the use of a single modified electrode surface in multiple analytical determinations over several weeks. Many coexisting metal ions had little or no effect on the determination of lead(II). The developed method was applied to lead determination in potable water.

Standard Gibbs energies of transfer of ions across the water—acetophenone interface

Abstract The techniques of dc and ac cyclic voltammetry have been used to determine the standard Gibbs energies of transfer of some ions across the water—acetophenone interface. The results are compared with calculated values using the model of ionic solvation developed recently.

Ion transfer across the water-o-dichlorobenzene interface

Abstract The transfer of several ions across the water-o-dichlorobenzene interface has been investigated by d.c. and a.c. cyclic voltammetry. Standard Gibbs partition energies of the ions between water and o-dichlorobenzene were estimated from the half-wave potentials obtained experimentally.

Investigation of the ion transfer across the water-nitrobenzene interface by ac cyclic voltammetry

Abstract The technique of ac cyclic voltammetry has been applied to the study of ion transfer across the water-nitrobenzene interface. The reversibility of the ion transfer, as well as precise nw1/2 values, can easily be determined using this method, as demonstrated for the ions ClO4−, Cs+, and NO3−.

Differential Pulse Anodic Stripping Voltammetric Determination of Cobalt(II) with N‐p‐Chlorophenylcinnamohydroxamic Acid Modified Carbon Paste Electrode

A new preconcentration and voltammetric method was developed for the determination of Co(II) with N-p-chlorophenylcinnamohydroxamic acid (CPCHA) modified carbon paste electrode. The measurements were carried out using differential pulse anodic stripping voltammetry. The effects of several experimental parameters such as modifier composition in the carbon paste electrode, pH and concentration of supporting electrolyte, deposition potential, deposition time, and other instrumental parameters were studied for analytical application. A linear response was obtained in the concentration range 1 × 10−6– 4 × 10−5 M Co(II) with a detection limit of 3.3 × 10−7 M for a 5 min deposition time. A relative standard deviation of 3.1 % was obtained for eight successive determinations of 1 × 10−5 M Co(II). Many coexisting metal ions had little or no effect on the determination of cobalt(II). The method was applied for the determination of cobalt in vitamin B12. The new electrode offered many attractive properties such as high stability, self cleaning ability, the use of nondearated solutions and can be used repeatedly without regeneration.

Flow Injection Determination of Hydrogen Peroxide Using a Carbon Paste Electrode Modified with a Manganese Dioxide Film

Abstract A manganese dioxide film modified carbon paste electrode was developed for use as an amperometric sensor for the determination of hydrogen peroxide (H2O2) in ammoniacal aqueous solutions. The electrode showed a stable response towards H2O2 after electrochemical activation. Effects of flow rate, operating potential, concentration, injection volume and interferences were investigated. A linear response towards H2O2 from 5 μg.l−1 to 450 mg.l−1 and a detection limit (3 signal-to-noise ratio) of 4.7 μg.l−1 was found. The method was employed for the determination of H2O2 in rain water samples.

Voltammetry of drugs at the interface between two immiscible electrolyte solutions

In this review, the results of the electrochemical investigations made on the transfer of ionizable drugs at the interface between two immiscible electrolyte solutions (ITIES) in the last decade have been presented. In many of the studies, cyclic voltammetry has been used to investigate the transfer characteristics of the charged species and deduce their partition coefficients, which are very important parameters to infer the lipophilicity of drugs in biological systems. The electrochemical technique allows the precise determination of the distribution of ionic species between two phases in a wider pH range. Such studies point out the complexity of the distribution of ionizable compounds and offer a new approach to relate the structure of such compounds to their passive transport across biological membranes.

Synthesis and characterization of Y3+-doped TiO2 nanocomposites for photocatalytic applications

The TiO(2).[Y(2)O(3)](x) (x = 0.1-0.4) nanocomposites (NCs) with an average particle size of 74 nm were prepared by the method of chemical co-precipitation followed by hydrolysis (CPH). Their visible light photocatalytic activity was investigated for the degradation of congo red (CR) dye. All NCs showed improved degradation as compared to the polycrystalline samples of similar compositions prepared by the solid-state reaction (SSR) route (average particle size of a few micrometers), as well as to the pure TiO(2). The better photocatalytic activity of the NCs was attributed to their smaller particle size. Another comparison of the results with those obtained with Zn(2+)/Fe(3+) ions co-doped TiO(2) NCs, under similar experimental conditions, revealed that in the Y(3+)-doped NCs, particle size might not be the only factor responsible for the improved photocatalytic properties. It was concluded that the Y(3+) ion-mediated suppression of the unwanted e(-)/h(+) recombination could be the possible factor leading to additional enhancement.