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 arsenic in groundwater samples using Square Wave Anodic Stripping Voltammetry (SWASV), Differential Pulse Anodic Stripping Voltammetry (DPASV) and Normal Pulse Anodic Stripping Voltammetry (NPASV) are described. Good resolution of the species, arsenic (III) and arsenic (V) is achieved using SWASV. The reliability of the methods was checked by analyzing the total arsenic content of the samples by Hydride Generation Atomic Absorptioion Spectrophotometer and by analyzing prepared controlled laboratory standard solution. Since this technique is comparatively cheaper than other available techniques it could be a better analytical technique for arsenic speciation from water. In this study, the assessment of inorganic arsenic species in ground water of Kalkini (Madaripur) and Hajigonj (Chandpur) is reported. It shows that arsenic content in water in different locations is irregular. Most of the locations contain higher level of As(III) than As(V). The highest concentration of arsenic is found in Anayetnagor (554.46 ± 0.07 μg/L) of Kalkini and Raichar (562 ± 0.50 μg/L) of Hajigonj. However, the level of total arsenic and As(III) of most of the villages of the study areas are more than the WHO guideline value (50μg/L). Therefore a proper monitoring process should be evolved along with the development of methods to keep the water free from arsenic.

Construction of a reproducible, reliable and rugged iridium‐based microelectrode is described. Perfect electrical contact, Ir‐glass sealing and Ir disk morphology are the key points for obtaining reproducible voltammetric sensors. These points are discussed in detail and optimal fabrication conditions are given. Electron bombardment under vacuum yielded good soldering between Ir and Cu electrical cable. Reproducible polishing of the microelectrode to a mirror like Ir disk surface is obtained with silicon carbide pads and diamond paste using an automatic home made polisher. Cyclic voltammetry and optical microscopy have been used to characterize this microelectrode. Hgplated Ir‐based microelectrodes are prepared by electrodeposition of mercury on the iridium disk substrate. Reproducibility and reliability close to 100% have been obtained for Ir‐based microelectrode preparation, mercury layer deposition and trace metal measurements by differential pulse anodic stripping voltammetry (DPASV) and square wave anodic stripping voltammetry (SWASV) in synthetic solutions even at low ionic strength (10−3 M). Continuous measurements over long periods of time indicate that the Hg‐plated Ir‐based microelectrodes can be used for several days without renewal of the mercury layer. These microelectrodes were applied to lead and cadmium speciation studies directly in river waters by SWASV without any separation. The results show that free PbII and CdII concentrations as low as 0.5 nM and 0.1 nM respectively can be determined by direct measurements, without perturbing the medium. The lifetime of these microelectrodes in the present state of the art is more than 2 years.

Square wave anodic stripping voltammetry (SWASV) is an effective method for the detection of Cd(II), but the presence of Pb(II) usually has some potential and negative interference on the SWASV detection of Cd(II). In this paper, a novel method was proposed to predict the concentration of Cd(II) in the presence of Pb(II) based on the combination of chemically modified electrode (CME), machine learning algorithms (MLA) and SWASV. A Bi film/ionic liquid/screen- printed electrode (Bi/IL/SPE) was prepared and used for the sensitive detection of trace Cd(II). The parameters affecting the stripping currents were investigated and optimized. The morphologies and electrochemical properties of the modified electrode were characterized by scanning electron microscopy (SEM) and SWASV. The measured SWASV spectrograms obtained at different concentrations were used to build the mathematical models for the prediction of Cd(II), which taking the combined effect of Cd(II) and Pb(II) into consideration on the SWASV detection of Cd(II), and to establish a nonlinear relationship between the stripping currents of Pb(II) and Cd(II) and the concentration of Cd(II). The proposed mathematical models rely on an improved particle swarm optimization-support vector machine (PSO-SVM) to assess the concentration of Cd(II) in the presence of Pb(II) in a wide range of concentrations. The experimental results suggest that this method is suitable to fulfill the goal of Cd(II) detection in the presence of Pb(II) (correlation coefficient, mean absolute error and root mean square error were 0.998, 1.63 and 1.68, respectively). Finally, the proposed method was applied to predict the trace Cd(II) in soil samples with satisfactory results. Keywords: square wave anodic stripping voltammetry (SWASV), particle swarm, support vector machine, screen-printed electrode, heavy metals, Cd detection, soil pollution DOI: 10.25165/j.ijabe.20171005.2863 Citation: Zhao G, Wang H, Yin Y, Liu G. PSO-SVM applied to SWASV studies for accurate detection of Cd(II) based on disposable electrode. Int J Agric & Biol Eng, 2017; 10(5): 251–261.

Copper speciation in the presence of fulvic acids (FAs) was studied in chemically defined seawater by square wave anodic stripping voltammetry (SQWASV). A simple complexation model assuming a single type of ligand and a 1:1 reaction stoichiometry successfully explained the measured data. A conditional stability constant of 5.80 +/- 0.07 and a complexing capacity of 610 +/- 80 micromol Cu/g FAs were obtained. This conditional stability constant would correspond to 7.23 on a free copper ion basis. The complexation kinetics was easily followed by anodic stripping voltammetry (ASV) measurements, and complexation equilibria were not reached until approximately 12 h. Coupled to speciation studies, the toxicity of copper in the presence of FAs was studied with the sea urchin Paracentrotus lividus embryogenesis bioassay. A clear protective effect of FAs was observed on Cu toxicity, and this effect could be accurately explained by SQWASV Cu speciation measurements. Additional experiments in the presence of high Cu and FA concentrations were performed, and no extra toxicity of Cu-FA complexes was observed. These results are in agreement with metal bioavailability models and also underline the usefulness of ASV for determining copper bioavailability in the presence of natural organic matter.

The present work is aimed at the development of highly sensitive electrochemical sensor based on immobilization of 1-phenyl-N-(thiophen-2-ylmethyl)ethanamine (PTE) on glassy carbon electrode (PTEGCE) for the detection of cupric ions (Cu2+), employing electrochemical impedance spectroscopy (EIS) differential pulse anodic stripping voltammetry (DPASV) and square wave anodic stripping voltammetry (SWASV). Several experimental parameters were optimized including concentration of the modifier, pH, and scan rate, number of cycles, accumulation time, deposition potential and supporting electrolytes. The designed sensor showed nice voltammetric response in media of different pH, demonstrated good percentage recoveries and exhibited remarkable electrocatalytic activity. The designed sensor was also not interfered much by the presence of other metal ions. A wide linear range with very low limit of detection as compared to the reported methods reveal the applicability of our designed sensor as a preferred analytical tool. The limit of detection as low as 0.11 nM was obtained using PTEGCE. We expect that these results will let the chemists to apply this sensor for various metallic, organic and organometallic toxins with slight modification.

Voltammetric procedures for trace metals analysis in polluted natural waters using homemade bare gold-disk microelectrodes of 25- and 125-microm diameters have been determined. In filtered seawater samples, square wave anodic stripping voltammetry (SWASV) with a frequency of 25 Hz is applied for analysis, whereas in unfiltered contaminated river samples, differential pulse anodic stripping voltammetry (DPASV) gave more reliable results. The peak potentials of the determined trace metals are shifted to more positive values compared to mercury drop or mercury-coated electrodes, with Zn always displaying 2 peaks, and Pb and Cd inversing their positions. For a deposition step of 120 s at -1.1 V, without stirring, the 25-microm gold-disk microelectrode has a linear response for Cd, Cu, Mn, Pb and Zn from 0.2 microg L(-1) (1 microg L(-1) for Mn) to 20 microg L(-1) (30 microg L(-1) for Zn, Pb and 80 microg L(-1) for Mn). Under the same analytical conditions, the 125-microm gold-disk microelectrode shows linear behaviour for Cd, Cu, Pb and Zn from 1 microg L(-1) (5 microg L(-1) for Cd) to 100 microg L(-1) (200 microg L(-1) for Pb). The sensitivity of the 25-microm electrode varied for different analytes from 0.23 (+/-0.5%, Mn) to 4.83 (+/-0.9%, Pb) nA L micromol(-1), and sensitivity of the 125-microm electrode varied from 1.48 (+/-0.7%, Zn) to 58.53 (+/-1.1%, Pb nA L micromol(-1). These microelectrodes have been validated for natural sample analysis by use in an on-site system to monitor Cu, Pb and Zn labile concentrations in the Deûle River (France), polluted by industrial activities. First results obtained on sediment core issued from the same location have shown the ability of this type of microelectrode for in situ measurements of Pb and Mn concentrations in anoxic sediments.

Release of free-state ions from fulvic acid-heavy metal complexes via VUV/H2O2 photolysis: Photodegradation of fulvic acids and recovery of Cd2+ and Pb2+ stripping voltammetry currents

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.

Copper (II) complexation in northern California rice field waters: an investigation using differential pulse anodic and cathodic stripping voltammetry

Square-wave anodic stripping voltammetry of lead and cadmium at cylindrical graphite fiber microelectrodes with in situ plated mercury films

Bare boron-doped diamond electrode (BDDE) was applied for investigation of deposition/stripping processes of silver ions in various supporting electrolytes. The highest signal was observed in 0.1 mol dm−3 HNO3. Detection of silver ions is also possible in 0.1 mol dm−3 Na2S2O3 where Ag+ is strongly complexed as [Ag(S2O3)2]3−. Though the sensitivity is 100 times lower, the potential of anodic dissolution of silver is significantly shifted towards the negative values. This shift might be useful for solving of some interferences which may occur in the detection process. After preliminary cyclic voltammetry, the analytical performance was studied by differential pulse anodic stripping voltammetry (DPASV) and square-wave anodic stripping voltammetry. Deposition potential of − 0.18 V vs. Ag/AgCl and deposition time of 240 s were selected as optimum DPASV parameters. The lowest detection limit of 2.0 × 10–10 mol dm−3 was achieved with DPASV in HNO3. Negligible effect of possible interferents on Ag response proved to be a good selectivity of method. The proposed method after validation was also applied to real samples analysis of some commercial products with complex matrix. The obtained results are statistically identical with data declared by manufacturer and gained by independent technique, making this method suitable for commercial product control.

The purpose of this study was to develop an inexpensive, simple, and highly selective cork-modified carbon paste electrode for the determination of Pb(II) by differential pulse anodic stripping voltammetry (DPASV) and square-wave anodic stripping voltammetry (SWASV). Among the cork–graphite electrodes investigated, the one containing 70% w/w carbon showed the highest sensitivity for the determination of Pb(II) in aqueous solutions. Under SWASV conditions, its linear range and relative standard deviation are equal to 1–25 µM and 1.4%, respectively; the limit of detection complies with the value recommended by the World Health Organization. To optimize the operating conditions, the selectivity and accuracy of the analysis were further investigated by SWASV in acidic media. Finally, the electrode was successfully applied for the determination of Pb(II) in natural water samples, proving to be a sensitive electrochemical sensor that meets the stringent environmental control requirements.

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

Rapid and simultaneous electrochemical method to measure copper and lead in canine liver biopsy

In-flow speciation of copper, zinc, lead and cadmium in fresh waters by square wave anodic stripping voltammetry Part II. Optimization of measurement step