Sensitive voltammetric determination of gallium in aluminium materials using renewable mercury film silver based electrode

Simple cyclic renewable silver amalgam film electrode (Hg(Ag)FE), applied for the determination of gallium(III) using differential pulse anodic stripping voltammetry (DP ASV), is presented. The effects of various factors such as: preconcentration potential and time, pulse height, step potential and supporting electrolyte composition are optimised. The calibration graph is linear from 5?nM (0.35?µg?L^?1) to 80?nM (5.6?µg?L^?1) for a preconcentration time of 60?s, with correlation coefficient of 0.995. For a Hg(Ag)FE with a surface area of 9.9?mm² the detection limit for a preconcentration time of 120?s is as low as 0.1?µg?L^?1. The repeatability of the method at a concentration level of the analyte as low as 3.5?µg?L^?1, expressed as RSD is 3.2% (n?=?5). The proposed method was successfully applied by studying the synthetic samples and simultaneously recovery of Ga(III) from spiked aluminium samples.     

Cyclic voltammetric studies of heat treated and oxidized carbon fibres in organic and aqueous solutions

Summary Cyclic voltammetry was used to compare the electrochemical behaviour ofPAN-based carbon fibre electrodes in aqueous (differentpH), acetonitrile and methanol solutions. The sets of fibres used were produced at three temperatures and were oxidized with conc. HNO₃ or left nonmodified. The electrode reaction meachanisms probably occurring on the carbon fibre surfaces were analyzed.

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Untersuchung thermisch behandelter und oxydierter Kohlefasern mittels zyklischer Voltammetrie in organische und wässrigen Lösungen

Zusammenfassung Es wurde das elektrochemische Verhalten von Kohlefaserelektroden in wassrigen (verschiedenerpH-werl), acetonitrilischen und methanolischen Lösungen verglichen. Die Kohlefasern aufPAN(Polyacrylnitril)-Basis, die sich voneinander in der Temperatur der termischen Behandlung unterscheiden und nicht oder mit konzentrierter Salpetersäure oxidiert wurden, wurden mittels zyklischer Voltammetrie untersucht. Der wahrscheinliche Verlauf der Elektrodeprozesse auf den Kohlefasernoberflächen wurde analysiert.

     

Square wave voltammetric determination of nitrofurantoin in pharmaceutical formulations on highly boron-doped diamond electrodes at different boron-doping contents

The influence of the boron-doping levels in boron-doped diamond film electrodes on the electrochemical response of nitrofurantoin (NFT) and the development of an electroanalytical procedure for NFT determination were investigated. The investigations were carried out using the techniques of cyclic voltammetry and square wave voltammetry on diamond film electrodes with different boron-doping levels (i.e., 5000, 10,000 and 20,000 mg L⁻¹). The level of boron-doping in the diamond film electrodes influenced the electrochemical reduction of NFT. The appropriate cyclic voltammetric response of NFT was obtained with Britton-Robinson buffer at pH 4 and for diamond films doped with 10,000 and 20,000 mg L⁻¹ of boron. These two films were selected for the development of the electroanalytical procedure. The use of square wave voltammetry with the optimized parameters demonstrated a good linear relationship between the peak current and the NFT concentration for a wide range of concentration. The lower limit of detection for the electrodes doped with 10,000 and 20,000 mg L⁻¹ of boron were 2.69 × 10⁻⁸ mol L⁻¹ (6.40 μg L⁻¹) and 8.15 × 10⁻⁹ mol L⁻¹ (1.94 μg L⁻¹), respectively, while the lower limits of quantification were 8.96 × 10⁻⁸ mol L⁻¹ (21.33 μg L⁻¹) and 2.72 × 10⁻⁸ mol L⁻¹ (6.47 μg L⁻¹), respectively. The applicability of the proposed procedure was tested using a commercial pharmaceutical formulation of NFT, and the results were compared with the procedure recommended by the British Pharmacopeia. The proposed procedure was sensitive, accurate and precise for analysis of NFT and did not require complex preparations or renovations of the electrode surface. This presents the advantage of eliminating mercury waste and minimizing the adsorptive problems related to the use of other electrodic solid surfaces.     

Time-derivative cyclic voltabsorptometry for voltammetric characterization of catechin film on a carbon-paste electrode: one voltammogram becomes four

Using (+)-catechin electrodeposited on a carbon-paste electrode as a model system, we have demonstrated the usefulness of the time-derivative cyclic voltabsorptometry for voltammetric characterization of the deposited films, in the case when not only the deposited species but also the same ones in free solution participated in redox processes. A long-optical-path thin-layer cell was used for the voltabsorptometric measurements. The potential-dependent absorption signals were monitored for catechin at 252 and 279 nm in B-R buffer electrolytes with pH = 1.8. The combination of voltabsorptometry with voltammetry enabled one measured cyclic voltammogram to become four, which were attributed to catechin and its oxidized state, in free solution or in deposited state, respectively. The surface coverage of the electrode was evaluated from the cyclic voltammograms obtained for the deposited catechin, which decreased with the increasing scan rate. Also, the deposited species was found to make a major contribution to the total voltammetric current, especially at higher scan rates.     

Differential pulse anodic stripping voltammetry detection of metallothionein at bismuth film electrodes

As a representation of metalloproteins, metallothionein (MT), which plays important biological and environmental roles such as in the metabolism and detoxification of some metals, was detected at bismuth film electrode (BiFE) by differential pulse anodic stripping voltammetry (DPASV). In pH 2–5.5, two well-defined anodic peaks were produced and attributed to the Zn²⁺ and Cd²⁺ inherent to MT. The calibration plot of DPASV peak currents for Cd²⁺ inherent to MT versus MT concentrations showed a good linearity with a detection limit of 3.86 × 10⁻⁸ mol/L for MT. As a non-toxic excellent electrode material, BiFE shows good performance for detecting MT, and is expected to find further applications in the studies of many other metalloproteins.     

Catalytic adsorptive stripping voltammetric measurements of trace vanadium at bismuth film electrodes

Bismuth-coated glassy carbon electrodes have been successfully applied for catalytic adsorptive stripping voltammetric measurements of low levels of vanadium(V) in the presence of chloranilic acid (CAA) and bromate ion. The new protocol is based on the accumulation of the vanadium-chloranilic acid complex from an acetate buffer (pH 5.5) solution at a preplated bismuth film electrode held at −0.35 V (versus Ag/AgCl), followed by a square-wave voltammetric scan. Factors influencing the adsorptive stripping performance, including the CAA and bromate concentrations, solution pH, and accumulation potential or time have been optimized. The response compares favorably with that observed at mercury film electrodes. A linear response is observed over the 5-25 μg/L concentration range (2 min accumulation), along with a detection limit of 0.20 μg/L vanadium (10 min accumulation). High stability is indicated from the reproducible response of a 50 μg/L vanadium solution (n = 25; R.S.D. = 3.1%). Applicability to a groundwater sample is illustrated.     

Cyclic voltammetric studies of the antipsychotic chlorpromazine using an alkylthiol/phospholipid-modified gold electrode

Self-assembled monolayers of alkanethiols on gold have been reported to be highly stable for voltammetry experiments in aqueous electrolyte. In this work a gold electrode has been modified by first depositing one layer of an alkylthiol (S-C₁₈) and then coating by phospholipid multilayers. Voltammetric oxidation of the antipsychotic chlorpromazine at this two-step modified electrode was followed by means of cyclic voltammetry measurements. The results give important information concerning the behaviour of the pharmacological agent at the lipid-water interface. Measurements made using the pre-concentration method allow good sensitivity improvement after 5 min accumulation time. The ability of chlorpromazine to penetrate inside the phospholipid multilayers has also been investigated under different conditions such as the nature of the phospholipid and the pH of the medium. The accumulation process seems to be closely related to the charge carried by the phospholipid and by the molecule, while the incorporation process seems to be independent of the charge carried by the phospholipid and dependent of the degree of fluidity of their hydrocarbon chains. We found through this work that the acid-base equilibrium of chlorpromazine together with its amphiphilic properties (as compared with the results of similar studies on phenothiazine) could be responsible for governing the principal aspects of the drug's behaviour toward biological membranes. Received: 6 January 1997 / Accepted: 27 February 1997     

Functioning of antimony film electrode in acid media under cyclic and anodic stripping voltammetry conditions

New insights into the functioning, i.e. electrochemical behaviour and analytical performance, of in situ prepared antimony film electrodes (SbFEs) under square-wave anodic stripping (SW-ASV) and cyclic (CV) voltammetry conditions are presented by studying several key operational parameters using Pb(II), Cd(II) and Zn(II) as model analyte ions. Five different carbon- and metal-based substrate transducer electrodes revealed a clear advantage of the former ones while the concentration of the precursor Sb(III) ion exhibited a distinct influence on the ASV functioning of the SbFE. Among six acids examined as potential supporting electrolytes the HNO₃ was demonstrated to yield nearly identical results in conducting ASV experiments with SbFE as so far almost exclusively used HCl. This is extremely important as HNO₃ is commonly employed acidifying agent in trace metal analysis, especially in elemental mass spectrometry measurements. By carrying out a systematic CV and ASV investigation using a medium exchange protocol, we confirmed the formation of poorly soluble oxidized Sb species at the substrate electrode surface at the end of each stripping step, i.e. at the potentials beyond the anodic dissolution of the antimony film. Hence, the significance of the cleaning and initializing the surface of a substrate electrode after accomplishing a stripping step was thoroughly studied in order to find conditions for a complete removal of the adhered Sb-oxides and thus to assure a memory-free functioning of the in situ prepared SbFE. Finally, the practical analytical application of the proposed ASV method was successfully tested and evaluated by measuring the three metal analytes in ground (tap) and surface (river) water samples acidified with HNO₃. Our results approved the appropriateness of the SbFE and the proposed method for measuring low μg L⁻¹ levels of some toxic metals, particularly taking into account the possibility of on-field testing and the use of low cost instrumentation.     

Square-wave voltammetric stripping analysis of thallium(III) at a poly(4-vinylpyridine)/mercury film electrode

A poly(4-vinylpyridine)/mercury film electrode (PVP/MFE) was used for the determination of trace thallium(III) by square-wave anodic stripping voltammetry (SWASV). Thallium(III) is preconcentrated onto the PVP/MFE as the anionic forms in chloride medium by the ion-exchange effect of the PVP. The high solubility of thallium in mercury further facilitates the accumulation effect. Various factors influencing the determination of thallium(III) were thoroughly investigated. This modified electrode displayed good resistance to interferences from surface-active compounds and common ions and increased sensitivity when used in conjunction with SWASV. In addition, detection can be achieved without deoxygenation and the electrode can be easily renewed. Applicability to various water samples is illustrated.     

Electrodeposition of mercury film on electrodes modified with clay minerals

A new type of carbon paste electrode modified with clay mineral and covered with a mercury film is presented in this work. Electrodeposition of the mercury film was performed on the carbon paste electrode modified with montmorillonite. The mercury film was deposited by both electrodeposition in situ and a preliminary electrodeposition. The pre-deposited film of mercury showed to be suitable for anodic stripping voltammetry. An open-circuit sorption of Cd, Pb, and Cu with subsequent anodic stripping voltammetry exhibited higher current responses of metals. Besides the enhanced sensitivity superior separation of the current responses during a simultaneous stripping of metals is expected to be achieved by means of the newly prepared electrode. Presented at the 57th Congress of Chemical Societies, Tatranské Matliare, 4–8 September 2005.     

Cyclic voltammetric and computational study of a 4-bromophenyl monolayer on a glassy carbon electrode

A glassy carbon (GC) surface modified with monolayer of 4-bromophenyl was examined as voltammetric electrode for some redox systems. The modified electrode exhibited very slow electron transfer in comparison to the unmodified surface by factors which varied with the redox systems. However, after scanning the modified electrode in 0.1 M tetrabutylammonium tetrafluoroborate (TBABF₄) in acetonitrile from 0.4 to −1.1 V vs. Ag/AgCl for 20–25 cycles, the modified electrode showed much faster electron transfer kinetics, e.g., the results for Fe(CN)₆ ^3−/4− were approaching those observed with unmodified surfaces. The effect is attributed to an apparently irreversible structural change in the 4-bromophenyl monolayer, which increases the rate of electron tunneling. The transition to the conducting state is associated with electron injection into the monolayer and causes a significant decrease in the calculated HOMO-LUMO gap for the monolayer molecule. Once the monolayer is switched to the conducting state, it supports rapid electron exchange with the redox system, but not with dopamine, which requires adsorption to the electrode surface. A conductive surface modified electrode may have useful properties for electroanalytical applications and possibly in electrocatalysis. Correspondence: Abbas A. Rostami, Department of Chemistry, Faculty Basic of Science, University of Mazandaran, Babolsar, Iran.     

The effect of the electrolyte concentration in the solution on the voltammetric response of insertion electrodes

A solid-state redox reaction involving an insertion of ions is analyzed with respect to the influence of the concentration of inserting ions in the solution phase. The voltammetric response is independent of the mass transfer in the solution provided that z = (D _ss/D _aq)^1/2 ρ/[C⁺]* is smaller than 0.1 (D _ss: diffusion coefficient of the cation C⁺ in the crystal; D _aq: diffusion coefficient of the cation C⁺ in the solution; ρ: density of the solid compound; [C⁺]*: concentration of cations in the bulk of the solution). In real cases this condition will be satisfied at solution concentrations above 1 mol/l. Received: 15 December 1997 / Accepted: 5 March 1998     

Adsorptive stripping voltammetric determination of trace concentrations of molybdenum at an in situ plated lead film electrode

An in situ plated lead film electrode has been applied for adsorptive stripping voltammetric determination of trace concentrations of molybdenum in the presence of Alizarin S. The procedure is based on the preconcentration of the molybdenum-Alizarin S complex at an in situ plated lead film electrode held at −0.6 V (versus Ag/AgCl), followed by a negatively sweeping square wave voltammetric scan. The peak current is proportional to the concentration of molybdenum over the range 2 × 10⁻⁹ to 5 × 10⁻⁸ mol L⁻¹, with a 3σ detection limit of 9 × 10⁻¹⁰ mol L⁻¹ with an accumulation time of 60 s. The measurements were carried out from underaerated solutions. The proposed procedure was validated in the course of Mo(VI) determination in water certified reference materials.     

Determination of Hg Traces in Gallium By Anodic Stripping Voltammetry on Glassy Carbon

Abstract

An A.S.V. method for determination of mercury in ultrapure gallium has been developed. The procedure is very simple and allows a sensitivity high enough to verify the highest purity level of Ga as concerns Hg traces (i.e. 1×10^?5 % Hg in Ga by weight).

The above method was applied to some samples of gallium used in this laboratory.     

Simultaneous determination of copper and lead in seawater using optimised thin-mercury film electrodes in situ plated in thiocyanate media

In the present work the anodic stripping voltammetric (ASV) methodology using a thin mercury film electrode in situ plated in thiocyanate media was re-assessed in order to allow the simultaneous determination of copper and lead in seawater. Under previously suggested conditions [6], i.e. using a concentration of thiocyanate of 5 mM, the ASV peaks of copper and lead overlapped due to the formation of a stable copper(I)-thiocyanate species, limiting the analytical determinations. Therefore, the best value for the thiocyanate concentration was re-evaluated: for 0.05 mM a trade-off between good resolution of the copper and lead peaks and high reproducibility of the mercury film formation/removing processes was achieved. In this media, the ASV peaks for Pb and Cu occurred, separated by 140 mV. Also, the in situ thin mercury film electrode was produced and removed with good repeatability, which was confirmed by the relative standard deviation values for the ASV determinations: 0.5% for Pb and 2.0% for Cu (10 replicate determinations in a solution with metal concentrations 1.5×10⁻⁸ M for lead and 2.2×10⁻⁸ M for copper). The optimised methodology was successfully applied to the determination of copper in the presence of lead, in certified seawater (NASS-5).     

Determination of ultratrace lead with bismuth film electrodes based on magneto-voltammetry

A novel method for the determination of Pb²⁺ with bismuth film electrodes (BFEs) based on magneto-voltammetry was investigated. In the presence of a 0.6?T external magnetic field, square wave voltammetry of Pb²⁺ was performed with BFEs. A high concentration of Fe³⁺ was added to the analytes to generate a large cathodic current during the preconcentration step. A Lorentz force from the flux of net current through the magnetic field resulted in convection. Then, more Pb²⁺ deposited onto the electrode and larger stripping peak currents were observed. BFEs that were prepared by simultaneously depositing the bismuth and Pb²⁺ on an electrode offered a mercury-free environment for this determination. This method exhibits a high sensitivity of 4.61?µA?µM^?1 for Pb²⁺ over the 1?×?10^?8 to 1?×?10^?6?M range. A detection limit as low as 8.5?×?10^?10?M was obtained with only 1-min preconcentration. The method was successfully applied to determine Pb²⁺ in real water samples.     

A study of bismuth-film electrodes for the detection of trace metals by anodic stripping voltammetry and their application to the determination of Pb and Zn in tapwater and human hair

This work reports the simultaneous determination of Cd(II), Pb(II) and Zn(II) at the low μg l⁻¹ concentration levels by square wave anodic stripping voltammetry (SWASV) on a bismuth-film electrode (BFE) plated in situ. The metal ions and bismuth were simultaneously deposited by reduction at −1.4 V on a rotating glassy carbon disk electrode. Then, the preconcentrated metals were oxidised by scanning the potential of the electrode from −1.4 to 0 V using a square-wave waveform. The stripping current arising from the oxidation of each metal was related to the concentration of each metal in the sample. The parameters for the simultaneous determination of the three metals were investigated with the view to apply this type of voltammetric sensor to real samples containing low concentrations of metals. Using the selected conditions, the limits of detection were 0.2 μg l⁻¹ for Cd and for Pb and 0.7 μg l⁻¹ for Zn at a preconcentration time of 10 min. Finally, BFE's were successfully applied to the determination of Pb and Zn in tapwater and human hair and the results were in satisfactory statistical agreement with atomic absorption spectroscopy (AAS).     

Activation of titanium electrodes for voltammetric detection of oxygen and hydrogen peroxide in alkaline media

Bright, freshly-polished Ti electrodes give minimal cathodic response for O₂ and H₂O₂ in 1.0 M NaOH. However, the response is increased gradually by repeated application of a triangular waveform within the approximate potential limits of O₂ response (ca. −1.5 to −0.7 V vs. SCE). This same voltammetric pretreatment applied for excessive periods results in formation of golden films on the Ti surfaces that are active for reduction of O₂ and H₂O₂. Levich plots of cathodic current for O₂ and H₂O₂ at rotated golden-Ti disk electrodes in 1.0 M NaOH (−1.35 V) are linear over a large range of rotational velocity (42 to 513 rad s⁻¹), a behavior considered to be indicative of fast heterogeneous kinetics. Ring-disk data demonstrate that a small amount of H₂O₂ is produced throughout the potential region for O₂ reduction and H₂O₂ is concluded to be an intermediate product in the O₂-reduction mechanism. These observations are consistent with those reported previously for single-crystal TiO₂ electrodes.     

Effect of model organic compounds on square-wave voltammetric stripping analysis at the Nafion/chelating agent mercury film electrodes

The effect of various organic compounds on the Nafion/chelating agent mercury film electrodes (NCAMFEs) in square-wave anodic-stripping voltammetry (SWASV) is explored. Two chelating agents used to prepare the NCAMFEs are dimethylglyoxime and 2,2'-bipyridyl. Triton X-100, sodium dodecyl sulfate, albumin, gelatin, starch, camphor, and humic acid are used as model organic compounds, while cadmium, lead, and copper are used as test metal ions. The NCAMFEs are considerably more resistant to organic interferences than the Nafion-coated mercury film electrode. The implications of these interferences for the reliability and feasibility of stripping measurements using the NCAMFEs in real samples are discussed. Results presented for untreated urine and natural water samples demonstrate the analytical utility of the NCAMFEs in SWASV.