Pulse Voltammetric Method For Determination Research Articles

Oxidation Mechanism of Fluorescein at Glassy Carbon Electrode

AbstractThis study investigates redox properties of fluorescein (FLSC), a fluorescent tracer with many applications in several areas, markedly in biochemical research and health care diagnosis, on glassy carbon electrode (GCE) at a wide interval of pH by using voltammetric techniques. Three peaks were observed at different potentials. The investigation revealed that FLSC is irreversibly electroxidized under a diffusion‐controled and pH–dependent process. The oxidation process in acid and physiological media occurs in two consecutive steps with formation of a main electroactive oxidation product in acid medium. Both oxidation steps involve the transfer of one electron and one proton, corresponding to the oxidation of phenolic groups with formation of ortho‐quinone derivatives, which are reversibly reduced to form catechol derivatives, and/or polymeric products. One electron and one proton are removed from the phenolic group at the position C6’ at the first step and at position C3’ at the second step. The diffusion coefficient of FLSC was assessed in pH=7.0 phosphate buffer (9.77×10−5 cm2 s−1). A differential pulse voltammetric method for determination of FLSC in physiological medium was also proposed.

Voltammetric determination of penicillin V in pharmaceutical formulations and human urine using a boron-doped diamond electrode

Simple, sensitive and selective differential pulse voltammetric method for determination of penicillin V on a bare (unmodified) boron-doped diamond electrode has been developed. Penicillin V provided highly reproducible and well-defined irreversible oxidation peak at very positive potential of +1.6V (vs. Ag/AgCl). The optimum experimental conditions for oxidation of penicillin V were achieved in acetate buffer solution (pH 4.0). The modulation amplitude of 0.1V, modulation time of 0.05s and scan rate of 0.05Vs−1 were selected as optimum instrumental parameters for differential pulse voltammetry. Linear response of peak current on the concentration in the range from 0.5 to 40μM with coefficient of determination of 0.999, good repeatability (RSD of 1.5%) and detection limit of 0.25μM were observed without any chemical modifications and electrochemical surface pretreatment. The effect of possible interferents such as stearic acid, glucose, urea, uric acid and ascorbic acid appeared to be negligible which evidently proved the good selectivity of method. The practical analytical utility of proposed method was demonstrated by determination of penicillin V in pharmaceutical formulations (tablets) and human urine samples with satisfactory recoveries (from 98 to 101% for tablets and 97 to 103% for human urine).

Study of the voltammetric behaviour of maleic hydrazide and its determination at a hanging mercury drop electrode

Voltammetric behaviour of maleic hydrazide pesticide dissolved in a Britton–Robertson buffer was investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). It was found that the process at the Hg electrode was diffusion controlled; the reaction was irreversible and involved a change of one proton and a transfer of one electron. A quantitative differential pulse voltammetric method for determination of maleic hydrazide was developed on the basis of these studies involving the reduction of the compound at a hanging mercury drop electrode. A linear calibration was obtained in the range of 0.5–5.5mgl−1, and the developed DPV methodology was then applied for the determination of maleic hydrazide in spiked vegetable samples by the standard addition method. Satisfactory percentage R.S.D. (∼2%), percentage recovery values (∼85%) and LOD (0.215mgl−1) were obtained. These compared well with the results from the alternative spectrophotometric method.

Electrocatalytic effects of deoxyribonucleic acids, adenine and guanine on the reduction of Ni(II) at a mercury electrode

Adenine, guanine, and native and denatured DNA lower the overpotential for the reduction of Ni(II) at a mercury electrode in a sodium acetate medium. A mechanism for the electrode reaction underlying the electrocatalytic effects observed is proposed. The similarity of the electrocatalytic effects of native and thermally denatured DNA adsorbed on the electrode at full coverage reveals that Ni(II) species interact with basic residues within the double-helical structure, thus reflecting the high diffusivity of these species throughout the native DNA molecule. A simple differential pulse voltammetric method for the simultaneous determination of adenine and guanine in mixtures based on the peak for the reduction of protonated adenine and the single prepeak produced by the reduction of Ni(II) catalysed by unprotonated adenine and guanine was developed. Finally, a sensitive adsorptive stripping differential pulse voltammetric method for the determination of native and denatured DNA is proposed.

Application of Cold Vapor Differential Pulse Voltammetric Method for Determination of Mercury in Urine Samples

Differential pulse stripping voltammetry was applied in the determination of mercury in urine samples. The mercury in the samples was oxidized to Hg(II) using bromine and KMnO4. Hg(II) was reduced by NaBH4to the metallic state and volatilized using nitrogen as the carrier gas. The gas containing mercury vapor was dried and accumulated on a gold plated impregnated graphite electrode. The stripping process was performed from 0.1MHClO4+ 3 × 10−3MHCl solution. The calibration graph was linear from 1 to 10 μg L−1of mercury in urine sample. The relative standard deviation for 8 μg L−1of mercury was 6.6%. The detection limit was 0.4 μg L−1of mercury.