Linear Scan Anodic Stripping Voltammetry Research Articles

Development and characterization of a clay-HDTMABr composite for the removal of Cr(VI) from aqueous solutions with special emphasis on the electrochemical interface

This research aims to study the removal of chromium in its toxic form, Cr (VI), from wastewater, using clay and modified clay with Hexadecyltrimethyl ammonium bromide (HDTMABr)as adsorbents. The modified clay is obtained by impregnating a known quantity of HDTMABr into the clay. The two materials were characterized by different techniques, such as X-ray diffraction, which is used to determine the inorganic composition and the phyllite structures it contains. Thermal analysis TGA isused to understand the thermal behavior as function of the sintering temperature. Nitrogen adsorption/desorption is used to get the pores' size and surface area, using the Brunauer-Emmett-Teller (BET) theory. Scanning electron microscopy (SEM) coupled with Energy Dispersive X-ray Spectroscopy (SEM/EDAX) is used to study the surface morphology of the bare clay and the HDTMABr/clay. The operating conditions, such as contact times, pH, and adsorption temperatures, were studied, and optimized to improve the efficiency of the adsorption process. The adsorption is favored in acidic medium and room temperature, giving adsorption capacities for Cr(VI) of 12 mg/g and 250 mg/g for the clay and clay/HDTMABr, respectively. The reaction kinetics were studied and found to fit a pseudo-second-order model. The standard entropy (ΔS°), enthalpy (ΔH°), and Gibbs free energy (ΔG°) changes indicate that the chromium (VI) adsorption process is a physical, spontaneous, endothermic process. Cyclic voltammetry (CV) and the electrochemical impedance spectroscopy (EIS) are used for the electrochemical characterization of the raw clay and clay/HDTMABr in [Fe(CN)6]3-/4-/ 0.1 M KCl solution. The linear scan anodic stripping voltammetry (LSASV) is used for the reduction the Cr(VI) to Cr(III), indicating that Cr(VI) accumulates better at the surface of clay/HDTMABr compared to the bare graphite and the raw clay.

Electrochemical immunoassay of antibodies using freshly prepared and aged conjugates of silver nanoparticles

In this work, silver nanoparticles (AgNPs) were conjugated with immunoglobulins G using a simple passive adsorption method and the composition and properties of freshly prepared (Ab@AgNPs) and aged (Ab@AgNP/Ag2SNPs) conjugates were investigated for the first time by transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and voltammetry. It was found that the state of the AgNPs in the conjugates changed during storage. In the freshly prepared Ab@AgNPs conjugates, silver is present in the metallic state only, while the aged Ab@AgNP/Ag2SNPs conjugates are characterized by the presence of a metallic core of AgNPs coated with a “corona” of Ag2S. This affects the selection of voltammetric conditions for recording an analytical signal from the silver label in the conjugates. The Ab@AgNPs and Ab@AgNP/Ag2SNPs conjugates were successfully tested in the electrochemical immunoassay of dog immunoglobulins as a model. A solid-phase indirect non-competitive assay was performed using a 96-well ELISA plate. To record intense analytical signals from the silver conjugates by linear scan anodic stripping voltammetry (LSASV) on a carbon composite electrode (CCE), they were preliminarily dissolved in acidic solutions. In the case of the Ab@AgNPs conjugate, a nitric acid solution (1 mol L−1) was used to dissolve silver conjugates, while in the case of Ab@AgNP/Ag2SNPs, a 1:1 mixture of 1 mol L−1 CH3COOH and 1 mol L−1 HNO3 was used. The CH3COOH dissolved the Ag2S “corona”, and HNO3 dissolved the silver core of the Ab@AgNP/Ag2SNPs conjugate.This work opens up the possibility of the prolonged use of silver conjugates in electrochemical immunoassay, which can be used in commercial test systems for immunological studies as an alternative to conjugates labelled with enzyme labels.

An insight to the filtration mechanism of Pb(II) at the surface of a clay ceramic membrane through its preconcentration at the surface of a graphite/clay composite working electrode

The use of cyclic voltammetry (CV) and linear scan anodic stripping voltammetry (LSASV) to predict the selectivity of microfiltration ceramic membranes made from a lump of local clay towards Pb(II) ions filtration is described. The membranes were characterized by different techniques followed by CV analysis of the Fe(CN)63-/Fe(CN)64- redox couple and Pb(II) on bare graphite, raw clay, and clay-modified carbon paste electrode (clay-modified CPE). The effect of clay loading in the range of 1–10 % (w/w) on the electrodes is studied, where an enhanced peak current is observed for 5 % w/w clay. Moreover,adecreaseinthepeak current can be seen for bare graphite electrodes, suggesting that the clay mineral had played asubstantial role in the sieving of heavy metal ions through theceramic membrane. The electroactive surface area of 5% w/w raw clay towards Fe(II) ions was found to be in the order of 3.07 × 10-2 cm2 and higher than 5% w/w clay sintered to 1000 °C and bare graphite. CV analysis shows that both, 5 % w/w raw clay and 5 % w/w clay sintered to 1000 °C exhibited high peak currents towards Pb(II) ions. The mobility of the Pb(II) ions is found to increase when 5% w/w clay sintered to 1000 °C is utilized as membrane/electrode, leading to an increase in the amount of reduced Pb(II) ions on the surfaces of the clay membranes/electrodes. The study suggests successful filtration of Pb(II) ions through the proposed membrane/electrode and a much better accumulation than Fe(II) at the surface of the membrane/electrode before being subjected to filtration.

Anodic stripping voltammetric determination of copper(II) using a functionalized carbon nanotubes paste electrode modified with crosslinked chitosan

The development and application of a functionalized carbon nanotubes paste electrode (CNPE) modified with crosslinked chitosan for determination of Cu(II) in industrial wastewater, natural water and human urine samples by linear scan anodic stripping voltammetry (LSASV) are described. Different electrodes were constructed using chitosan and chitosan crosslinked with glutaraldehyde (CTS-GA) and epichlorohydrin (CTS-ECH). The best voltammetric response for Cu(II) was obtained with a paste composition of 65% (m/m) of functionalized carbon nanotubes, 15% (m/m) of CTS-ECH, and 20% (m/m) of mineral oil using a solution of 0.05 mol L −1 KNO 3 with pH adjusted to 2.25 with HNO 3, an accumulation potential of −0.3 V vs. Ag/AgCl (3.0 mol L −1 KCl) for 300 s and a scan rate of 100 mV s −1. Under these optimal experimental conditions, the voltammetric response was linearly dependent on the Cu(II) concentration in the range from 7.90 × 10 −8 to 1.60 × 10 −5 mol L −1 with a detection limit of 1.00 × 10 −8 mol L −1. The samples analyses were evaluated using the proposed sensor and a good recovery of Cu(II) was obtained with results in the range from 98.0% to 104%. The analysis of industrial wastewater, natural water and human urine samples obtained using the proposed CNPE modified with CTS-ECH electrode and those obtained using a comparative method are in agreement at the 95% confidence level.

Factors Influencing Redox Magnetohydrodynamic-Induced Convection for Enhancement of Stripping Analysis

Factors affecting the use of redox magnetohydrodynamics (MHD) to enhance the stripping analysis response to heavy metals have been investigated. The analytes were Pb2+, Cd2+, Cu2+, and Tl+ at concentrations ranging from 5 nM to 2 microM. Co-deposition of analytes with Hg2+ (to form a thin Hg film electrode) occurs along with reduction of a high concentration of Fe3+. The Fe3+ provides the high cathodic current necessary to produce a significant Lorentz force, and therefore enhanced convection and larger stripping signals and sensitivities, when the analysis is performed in the presence of an external magnetic field. The effects of varying Fe3+ concentration (1-100 mM), working electrode size (10 microm-3 mm), and magnetic field strengths (0-1.77 T) generated with electromagnets and NdFeB permanent magnets were investigated. Using 100 mM Fe3+ as the MHD-generating redox species at a 3-mm working electrode and in a magnetic field of 1.77 T, peak areas from linear sweep voltammetry were increased by as much as 159 +/- 5%, compared to the signal obtained in the absence of a magnetic field. Experimental detection limits as low as 5 nM were achieved with only a 1-min preconcentration time. A field strength as low as 0.12 T offers some signal enhancement with 100 mM Fe3+. While linear scan anodic stripping voltammetry was used primarily to obtain the signals after the deposition step, potentiometric stripping analysis was also investigated. Redox MHD is an attractive alternative convection method for applications involving sample volumes too small for mechanical stirring or for in-field applications using portable devices that cannot be complicated by the instrumentation required for mechanical stirring.

Numerical simulations of linear scan anodic stripping voltammetry at a modified square array of hemispherical microelectrodes located in a thin-layer cell

The finite element method has been used to simulate LSASV measurement at a loosely packed square array of recessed microdiscs and of hemispherical mercury microelectrodes located in a thin-layer cell. The mercury volume (radius=7.5 μm), the protective gel (thickness=300 μm) and the solution medium (thickness=200 μm) have been meshed. The concentrations of the reduced and oxidised species were linked both by the Nernst equation and the equality of the fluxes at the mercury|gel interface. Both overlapping of adjacent diffusion layers and depletion occurring in this finite box decrease the amount of species being reduced during the deposition step. However, the peak width ( W 1/2=39 mV) and peak potential ( E p− E ′0=−34.6±1 mV) of the resulting stripping current are independent of the deposition time. During the stripping step, the metal concentration at the surface of the electrode is much higher than the initial concentration. The time to reach a uniform concentration in the gel again after the voltammetric reoxidation step has been determined, for both single microelectrode and a square array, as a function of the deposition time, thus giving the maximum frequency of successive measurements that should be used. Agreement between simulated and experimental results confirms that diffusion is the predominant transport process occurring in such thin-layer cell. In addition, comparison with analytical expressions has been done whenever possible.

A study of Nafion-coated and uncoated thin mercury film-rotating disk electrodes for cadmium and lead speciation in model solutions of fulvic acid

The speciation of lead and cadmium in model solutions of a well characterized fulvic acid (FA), Laurentian FA, was investigated by anodic stripping voltammetry (ASV) using a thin mercury film-rotating disk electrode (TMF-RDE) and a Nafion-coated TMF-RDE. Pseudopolarograms were fitted to a model that accounted for differences in the diffusion coefficients between the free metal ion, M, and the metal complexes, ML, and the heterogeneity of naturally-occurring organic complexants, L, such as fulvic acid. The pseudopolarograms were used for each metal system to determine the differential equilibrium function which is independent of the experimental conditions and allows the stability constants for other metal loading conditions to be predicted. The experiments were done using linear-scan anodic stripping voltammetry (LSASV), differential pulse anodic stripping voltammetry (DPASV), and square wave anodic stripping voltammetry (SWASV) with an uncoated TMF-RDE and a Nafion-coated thin mercury film-rotating disk electrode (NCTMF-RDE). The NCTMF-RDE was investigated to determine its usefulness in preventing adsorption of surface-active organic complexants such as fulvic acid on the mercury electrode surface. LSASV was found to be the least susceptible to adsorption. DPASV was affected by adsorption in the lead-FA model solutions, and SWASV was strongly affected by adsorption in both the lead-FA model solutions and the cadmium-FA model solutions. The Nafion-coated TMF-RDE did not prevent adsorption when DPASV or SWASV was used. However, the results suggest that the Nafion-coated TMF-RDE may be useful in preventing adsorption when LSASV is used.

Electrochemical characterization of a microfabricated thick-film carbon sensor for trace determination of lead

An electrochemical sensor was fabricated by screen printing techniques. This sensor, coupled with stripping voltammetry, could provide a means for a relatively inexpensive on site detector for trace levels of heavy metals. The sensor consists of an electrode pair of graphite/carbon black working electrode and Ag/AgCl reference electrode printed onto a polycarbonate surface. Microscope observation of the working electrode shows considerable surface roughness. Cyclic voltammograms of ferricyanide and lead nitrate indicated that the electrochemical nature of the carbon working electrode and the reference electrode on the sensor were comparable to the performance of conventional glassy carbon and Ag/AgCl reference electrodes. Lead in the 10−6–10−9 M concentration range using linear scan anodic stripping voltammetry with identical deposition times resulted in a linear relationship between peak current and analyte concentration. Square-wave anodic stripping voltammetry is compared with alternative electroanalytical techniques and is shown to offer the advantage of rapid determination of lead in O2-containing solutions.

Linear-Scan Anodic Stripping Voltammetry with Thin-Film Electrodes: Theory of the Stripping Stage and Experimental Tests

The principles of thin-layer anodic stripping voltammetry, are discussed and a model for the stripping stage is developed for anodization by a linear potential ramp. The model assumes uniformity of the amalgam concentration, reversible electrode behavior, and planar diffusion of the stripped ions away from the anode. The entire shape of the stripping peak is then predicted from the model. Several stringent tests are developed to assess how well the model accords with experimental reality. One of these tests is analogous to the “log plot” of classical polarography. Another relates the peak current of the stripping voltammogram to its area. Experiments were carried out on amalgams of cadmium and lead formed by cathodic codeposition with the mercury onto an array of carbon microdisks in an unstirred solution, and the results have been used to test the model exhaustively. The results for lead amalgam agree well with the model, but agreement is less satisfactory for cadmium amalgam. A comparison is made of three rival methods of assaying the metal content of the amalgam.

Dynamics and Performance of Fast Linear Scan Anodic Stripping Voltammetry of Cd, Pb, and Cu Using In Situ-Generated Ultrathin Mercury Films

The dynamics of fast linear scan (LS) ASV for the simultaneous detection of Cd, Pb, and Cu was investigated at various scan rates (0.5-10 V/s) and at different metal ion concentrations (50-800 nM) utilizing ultrathin mercury films (9 nm) at a conventional size (d(0) = 1 mm) electrode. Results of the investigation show that when the thin films were utilized, diffusion of metals through the mercury film was not the rate-limiting step of the stripping process at moderate to fast scan rates (0.5-10 V/s). A fairly linear relationship between the peak height and scan rate was observed at scan rates (0.5-10 V/s) beyond the upper limit of the theoretical model for the behavior of LS-ASV. In addition, peak width at half-height (b(1/2)) as low as 33 mV was achieved at 0.5 V/s. The behavior of LS-ASV in terms of peak width at these scan rates is thus different from what the theoretical model of LS-ASV would have predicted. For the ultrathin mercury films, at least two additional factors, kinetics and concentration, have significant effects on practical LS-ASV. Experimental results show that the stripping process of Cu was primarily kinetic-controlled for fast scans, while those for Cd and Pb were dependent on both scan rates and concentrations. The ultrathin mercury film resulted in a significant enhancement of the ratio of signal-to-baseline slope (i(p)/Δi(b), a ratio used to measure the effectiveness of discrimination of the peak signal against the steep sloping baseline in LS-ASV) for Cd and Pb stripping peaks, but only a slight enhancement for Cu stripping peaks. The optimal performance of LS-ASV in terms of sensitivity, peak width, and enhancement of the i(p)/Δi(b) ratio for the three metals was achieved at 2 V/s. Because of the high reproducibility of the background currents of the stable in situ MTFs, background subtraction was carried out at 2 V/s with little hysteresis. This feature, combined with the enhancement of the i(p)/Δi(b) ratio at the fast scan rate of 2 V/s, allowed for the detection of sub-ppb levels of Cd, Pb, and Cu at a deposition time of 2 min.

Square wave and linear scan anodic stripping voltammetry at iridium-based mercury film electrodes

Discussion de la reponse voltammetrie lors de la dissolution anodique du plomb a une electrode en titane modifiee par une couche de mercure

Differential pulse anodic stripping voltammetry of cadmium(II) with a rotating membrane-covered mercury film electrode

A rotating membrane-covered mercury film electrode (MCMFE) was constructed by placing a dialysis membrane over a glassy carbon rotating disk electrode and plating a thin mercury film onto the electrode surface through the membrane. Differential pulse anodic stripping voltammetry of cadmium was used to evaluate the effects of pH, rotation rate, deposition time, and concentration on the MCMFE. The response was linear from 4.0 X 10/sup -9/ MCd/sup 2 +/ to 1.07 X 10/sup -5/ M Cd/sup 2 +/ with a standard deviation of +/- 9.30 X 10/sup -10/ M Cd/sup 2 +/ for a 1.78 X 10/sup -8/ M Cd/sup 2 +/ solution (RSD +/- 11.1%) and a standard deviation of +/- 6.44 X 10/sup -9/ M Cd/sup 2 +/ for a 1.78 X 10/sup -/' M Cd/sup 2 +/ solution (RSD +/- 3.64%). The limit of detection was estimated to be 8.6 X 10/sup -10/ M. These results compared favorably to the bare mercury film electrode (MFE) for linear scan anodic stripping voltammetry. 29 references, 5 figures.

Determination of arsenic in polluted waters by differential pulse anodic-stripping voltammetry

Experimental parameters affecting the analytical response of arsenic in differential pulse anodic-stripping voltammetry (DPASV) have been examined. DPASV offers higher sensitivity than linear-scan anodic-stripping voltammetry for similar analysis times. Both techniques have been applied to the NBS Standard Reference Water (SRM 1643) and some polluted water samples. The results on polluted waters compared favourably with those obtained by graphite-furnace atomic-absorption spectroscopy.

Convolution voltammetry of metal complexes

The application of convolution potential voltammetry to questions of metal complexation is described. Theoretical relations are derived to show that the stability constants may be directly related to the shift in the peak potential of the semiderivative wave, provided the complexes are labile. Equations are also given for inert and quasilabile complexes. Stability constants for the PbCl x and CdCl x systems are reported, illustrating the use of convolution techniques with linear scan voltammetry and with linear scan anodic stripping voltammetry. Advantages of convolution techniques are discussed.

Anodic Stripping Voltammetry with Superimposed A.C. Potential

AbstractThe combination of a. c. polarography with linear scan anodic stripping voltammetry has been investigated, employing a self‐constructed, phase discriminating a. c. attachment. The resolution and sensitivity of the method was compared with those obtainable, under similar experimental conditions, by plain anodic stripping voltammetry. Changes in the concentration of the supporting electrolyte and the presence of dissolved oxygen frequently affect the sensitivity and must be carefully controlled. The practical application of the method is illustrated by applying it to the determination of zinc in solutions and in a standard silicate sample.