Determination of traces of metals by anodic stripping voltammetry at a rotating glassy carbon ring—disc electrode: Part 1. Method and instrumentation with evaluation of some parameters

The equipment and procedure are described for the determination without preconcentration of several heavy metals based on d.c. anodic stripping voltammetry at a rotating ring—disc glassy carbon electrode with in situ mercury plating. During stripping of the metals deposited on the disc, the current from the reduction of the ions collected at the ring is measured. Some parameters (scan rate, thickness of the mercury film, electrode rotation and deposition time) influencing the ring collection peak current are examined experimentally. The results are compared with the theoretical considerations given by de Vries and van Dalen for anodic stripping voltammetry on a stationary mercury film electrode and by Bakanov et al. for a rotating mercury film electrode.     

In situ electrodeposition for the determination of lead and cadmium in sea water

Electrodeposition techniques for the direct determination of lead and cadmium in sea water at the natural pH and in the presence of dissolved oxygen are examined. Anodic stripping voltammetry, at either the hanging mercury drop electrode or glassy carbon thin film electrode, is suitable for the determination of labile lead and cadmium. The presence of dissolved oxygen increases the height of the lead wave with a shift to more negative potentials. A more versatile technique is in situ deposition of labile metals on a mercury-coated graphite tube electrode. The mercury film, deposited in the laboratory, is stable on the dried tubes which are used later for field electrodeposition. The deposited metals are determined by electrothermal atomic absorption spectrometry.     

Stripping analysis of heavy metals in tap water using the bismuth film electrode

A commercially available screen-printed carbon electrode coated with an ex situ deposited bismuth film (BiSPCE) has been applied to the determination of Pb(II) and Zn(II) ions in tap water (Barcelona water distribution network) by means of stripping voltammetry (SV) and stripping chronopotentiometry (SCP). A good reproducibility of the measurements and a satisfactory agreement between SV and SCP data were observed for both heavy metal ions. Although, in principle, the procedure could be also suited to the determination of Cd(II), this species was not detected. The results were also consistent with the routine ICP-OES measurements of the water distribution company, thus confirming the potential usefulness of such BiSPCE disposable devices for the analysis of heavy metals in natural waters.      

Combinatorial electrochemistry using metal nanoparticles: from proof-of-concept to practical realisation for bromide detection

Principles and practical application of combinatorial electrochemistry in search for new electroactive materials in electroanalysis have been explored. Nanoparticles of three different metals: silver, gold and palladium have been independently synthesized on the glassy carbon spherical powder surface by electroless deposition process and characterized using both spectroscopic and electrochemical techniques. These three materials were then combined together onto basal plane pyrolytic graphite electrode surface and the application of the combinatorial approach to find the electrode material for bromide detection as model target analyte was demonstrated. The component electroactive for bromide detection was next identified and it was found that silver nanoparticles were the active ones. A composite electrode based on silver nanoparticle modified glassy carbon powder and epoxy resin was then fabricated and it was found to allow accurate determination of bromide. The electroactivity for the bromide determination of the composite electrode was compared with that of a bulk silver electrode and it was shown that the composite electrode is very efficient with a comparable electroactivity with only a portion of precious metals being used for its construction.     

Development of a versatile,easy and rapid atmospheric monitor for benzene,toluene, ethylbenzene and xylenes determination in air

A new procedure for the passive sampling in air of benzene, toluene, ethylbenzene and xylene isomers (BTEX) is proposed. A low-density polyethylene layflat tube filled with a mixture of solid phases provided a high versatility tool for the sampling of volatile compounds from air. Several solid phases were assayed in order to increase the BTEX absorption in the sampler and a mixture of florisil and activated carbon provided the best results. Direct head-space-gas chromatography–mass spectrometry (HS-GC–MS) measurement of the whole deployed sampler was employed for a fast determination of BTEX. Absorption isotherms were used to develop simple mathematical models for the estimation of BTEX time-weighted average concentrations in air. The proposed samplers were used to determine BTEX in indoor air environments and results were compared with those found using two reference methodologies: triolein-containing semipermeable membrane devices (SPMDs) and diffusive Radiello samplers. In short, the developed sampling system and analytical strategy provides a versatile, easy and rapid atmospheric monitor (VERAM).     

Determination of trace metals by anodic stripping voltammetry using a bismuth-modified carbon nanotube electrode

A bismuth-modified carbon nanotube electrode (Bi-CNT electrode) was employed for the determination of trace lead, cadmium and zinc. Bismuth film was prepared by in situ plating of bismuth onto the screen-printed CNT electrode. Operational parameters such as preconcentration potential, bismuth concentration, preconcentration time and rotation speed during preconcentration were optimized for the purpose of determining trace metals in 0.1M acetate buffer solution (pH 4.5). The simultaneous determination of lead, cadmium and zinc was performed by square wave anodic stripping voltammetry. The Bi-CNT electrode presented well-defined, reproducible and sharp stripping signals. The peak current response increased linearly with the metal concentration in a range of 2-100 microg/L. The limit of detection was 1.3 microg/L for lead, 0.7 microg/L for cadmium and 12 microg/L for zinc (S/N=3). The Bi-CNT electrode was successfully applicable to analysis of trace metals in real environments.     

Polymer-Mercury Coated Screen-Printed Sensors for Electrochemical Stripping Analysis of Heavy Metals

In the perspective of in-field stripping analysis of heavy metals, the use and disposal of toxic mercury solutions (necessary to plate a mercury film on a carbon electrode surface) presents a problem. The aim of this work was the development of mercury coated screen-printed electrodes previously prepared in the lab and ready to use in-field. Thus some commercially available polymers like Nafion®, Eastman Kodak AQ29®, and Methocel® were investigated as mercury entrapping systems for electrochemical stripping analysis of heavy metals. Screen-printed disposable cells with a silver pseudo-reference electrode, a graphite counter electrode, and a graphite working electrode were used. To modify the sensor, the polymer solution was cast onto the carbon working electrode surface. Detection limits of 0.8 and 1 μg/L were obtained for lead and cadmium respectively. Since Methocel® based electrodes showed the best performance, they were used for the analysis of real samples. The results were compared with those obtained using a classical thin mercury film electrode and ICP spectroscopy.

All the experiments reported here were performed in un-deareated solutions as required for in-field analysis.     

The carbon nanotubes-polyaniline composites and their effect on catalytic properties of deposited catalysts

Composites of functionalized single-wall carbon nanotubes and polyaniline are deposited onto electrodes by in situ electrochemical polymerization. Their electrochemical behavior and differential capacitance are studied by cyclic voltammetry, electrochemical impedance spectroscopy, and chronovoltamperometry. The differential capacitance of the composite electrode exceeds that of pure polyaniline film deposited onto electrode, which can be explained by the nanotubes’ loosening effect on the polyaniline structure. The composite-electrode capacitance is as large as 1000 F g⁻¹ or higher. Thus obtained composite films were used as a support for deposited platinum-ruthenium catalyst. The Pt-Ru structure and catalytic properties in the methanol oxidation reaction are studied. It is shown that the specific current of methanol oxidation at Pt-Ru is larger by a factor of 7–15 than those measured when pure polyaniline, pure carbon nanotubes, or standard Vulcan XC-72 carbon black are used as supports. It is found that the catalytic activity is the same for all studied supports, provided the current is reduced to the unit of Pt-Ru true surface area. Thus, the observed large catalytic effect is associated with the structure and high dispersivity of the electrodeposited metals incorporated to the single-wall carbon nanotubes-polyaniline composite.     

Carbon-supported palladium catalysts for fuel cells

Small controlled amounts of palladium were electrochemically deposited onto various carbon supports from solutions of glycinate-chloride complexes of palladium(II) in order to obtain palladium catalysts suitable for use in fuel cells. The catalytic activity of the resulting catalytic layers was studied in reactions of reduction of atmospheric oxygen and oxidation of methanol and ethanol in acid and alkaline media by measuring cyclic voltammetric curves on a rotating disk electrode.     

Highly Sensitive Differential Pulse Voltammetric Determination of Cd,Zn and Pb Ions in Water Samples Using Stable Carbon‐Based Mercury Thin‐Film Electrode

A new carbon‐based mercury thin‐film electrode consisting of screen‐printed carbon on a low temperature co‐fired ceramic substrate was made. Ex‐situ mercury deposition in a potassium thiocyanate solution was used. This approach an electrode with high long‐term stability (>500 measurement cycles) and reproducibility (≤2 %) for sensitive determination of ultra trace heavy metals, using differential pulse anodic stripping voltammetry. The detection limits were 0.25, 0.08 and 5.5 ng mL^?1 for Cd(II), Pb(II), and Zn(II), respectively. The method was applied to the determination of the analytes in water, wastewater, lake water, and certified reference material samples with satisfactory results.     

A study on the electroanalytical performance of a bismuth film-coated and Nafion-coated glassy carbon electrode in alkaline solutions

Bismuth film electrodes are widely used for determination of heavy metal ions in acidic solutions, while alkaline solutions are rarely employed. We have compared the deposition of Bi(III) and Pb(II) on a Nafion-coated glassy carbon electrode in alkaline and acidic solutions. The results indicate that both Bi(III) and Pb(II) can be deposited in either alkaline or acidic solution, but the quantity of Pb(II) deposited in alkaline solution is less than that in acidic solution. The modified electrode was used to determine heavy metal ions in both alkaline and acidic solutions, and the results of the method agree well with those of atomic absorption spectroscopy.     

Determination of traces of copper by anodic stripping voltammetry at a rotating carbon paste disk electrode modified with poly(1,8-diaminonaphtalene)

In the present work, carbon paste electrodes (CPE) modified with conducting polymers 1,8-diaminonaphtalene (DAN) was developed for the voltammetric determination of Cu(II). The modified electrode exhibited a significantly increased sensitivity and selectivity for Cu²⁺ compared with a bare carbon paste electrode. Copper(II) was preconcentrated at open circuit on the modified electrode. The measurements were carried out using a rotating disk electrode (RDE) as working electrode. The experimental parameters for the determination of Cu(II) were optimized. The Cu(II) ions were chemically deposited onto the surface of poly DAN-CPE in an acidic medium. Under the optimum conditions, a linear calibration graph was obtained in the concentration range of 0.1 to 250 ppb with a correlation coefficient of 0.9998. The relative standard deviation for 6 successive determinations was 4.7%. A study of interfering substances was also performed, and the method was applied to the direct determination of copper in real samples like tap water and orange juice samples. The article is published in the original.     

Disposable Anodic Stripping Voltammetric Sensor for Heavy Metal Analysis in Environmental Samples

A disposable sensor was developed for anodic stripping voltammetric analysis of heavy metals utilizing the HgO-modified composite electrode technique. It was prepared by integrating a HgO-modified electrode, Ag/AgCl reference electrode and carbon counter electrode on a polycarbonate strip by screen printing technique.     

Biotinylated polypyrrole films: an easy electrochemical approach for the reagentless immobilization of bacteria on electrode surfaces

Biotinylated bacteria were immobilized onto biotin/avidin modified electrode surfaces. Firstly, an electrospotting deposition method, followed by fluorescence microscopy, showed that bacteria were specifically grafted onto a gold surface. Fluorescence intensity versus the quantity of bacteria deposited on the surface was correlated, allowing determination of the microbial saturation point. Secondly, biotinylated bacteria were immobilized onto a glassy carbon macro-electrode in order to assess immobilized bacterial denitrification activity. During a 7-day trial, the modified electrode completely denitrified 5 mM nitrate, with a rate of 1.66 mM/day over the first 3 days. When the same electrode was placed in fresh nitrate solution, the denitrification rate dropped to 0.80 mM/day. Crucially, the immobilized bacteria did not become detached from the electrode during the study.     

Nanostructured catalysts for cathodes of oxygen-hydrogen fuel cells

Bimetallic catalysts platinum-cobalt, platinum-chromium, and platinum-tungsten, deposited onto highly dispersed carbon black from complex cluster-type compounds of corresponding metals with a 1: 1 atomic ratio of metals are developed. The catalysts are characterized by methods of x-ray diffraction analysis and energy dispersive analysis of x-rays. The procedure involving use of a thin-film rotating disk electrode is employed to probe kinetic parameters of the oxygen reduction reaction on the catalysts developed. The investigated binary catalysts exhibit specific electrochemical characteristics that are not inferior and, in some cases, are superior to the characteristics intrinsic to the commercial platinum catalyst E-TEK, when tested in the composition of a gas-diffusion electrode under conditions that are close to real conditions in which cathodes of oxygen-hydrogen fuel cells operate.     

Electrocatalytic oxidation of hydrazine at a glassy carbon electrode modified with nickel ferrite and multi-walled carbon nanotubes

A hydrothermal technique was used to synthesize nickel ferrite nanoparticles (NF-NPs) deposited on multi-walled carbon nanotubes (MWCNTs). The material was characterized by scanning electron microscopy, energy dispersive spectrometry, and X-ray powder diffraction which showed that the NF-NPs are located on the surface of the carboxylated MWCNTs. The material was used to modify a glassy carbon electrode which then was characterized via cyclic voltammetry, electrochemical impedance spectroscopy, and amperometry. The electrode displays strong electrochemical response to hydrazine. A potential hydrazine sensing scheme is suggested.

Anodic stripping voltammetry of antimony at unmodified carbon electrodes

Antimony is an element of significant environmental concern, yet has been neglected relative to other heavy metals in electroanalysis. As such very little research has been reported on the electroanalytical determination of antimony at unmodified carbon electrodes. In this paper we report the electrochemical determination of Sb(III) in HCl solutions using unmodified carbon substrates, with focus on non-classical carbon materials namely edge plane pyrolytic graphite (EPPG), boron doped diamond (BDD) and screen-printed electrodes (SPE). Using differential pulse anodic stripping voltammetry, EPPG was found to give a considerably greater response towards antimony than other unmodified carbon electrodes, allowing highly linear ranges in nanomolar concentrations and a detection limit of 3.9?nM in 0.25?M HCl. Furthermore, the sensitivity of the response from EPPG was 100 times greater than for glassy carbon (GC). Unmodified GC gave a comparable response to previous results using the bare substrate, and BDD gave an improved, yet still very high limit of detection of 320?nM compared to previous analysis using an iridium oxide modified BDD electrode. SPEs gave a very poor response to antimony, even at high concentrations, observing no linearity from standard additions, as well as a major interference from the ink intrinsic to the working electrode carbon material. Owing to its superior performance relative to other carbon electrodes, the EPPG electrode was subjected to further analytical testing with antimony. The response of the electrode for a 40?nM concentration of Sb(III) was reproducible with a mean peak current of 1.07?µA and variation of 8.4% (n?=?8). The effect of metals copper, bismuth and arsenic were investigated at the electrode, as they are common interferences for stripping analysis of antimony.     

An electrochemical stripping method for the selective determination of traces of silver

A method has been developed for the determination of traces of silver in the presence of large concentrations of interfering metals, particularly copper, involving reduction of the silver on a glassy-carbon electrode modified by an adsorbed layer of previously deposited hydrogen.     

Stripping Voltammetric Determination of Pb(II) and Cd(II) Based on the Multiwalled Carbon Nanotubes-Nafion-Bismuth Modified Glassy Carbon Electrodes

Abstract

In this work, a new method for the simultaneous determination of Pb(II) and Cd(II) on the multiwalled carbon nanotubes (MWNT)-Nafion-bismuth modified glassy carbon electrode (GCE) using square-wave anodic stripping voltammetry has been studied. Scanning electron microscopy was used to investigate the characteristics of the MWNT-Nafion-bismuth modified GCE. Well-defined sharp stripping peaks were observed in the determination of Pb(II) and Cd(II) simultaneously on this electrode. Under optimized conditions, the lowest detectable concentrations were 50 ng/l for Pb(II) and 80 ng/l for Cd(II) under a 10 min preconcentration. The attractive performances of MWNT-Nafion-bismuth modified GCE demonstrated its application for a simple, rapid, and harmless determination of trace heavy metals.     

Determination of Trace Amounts of Copper in Tap Water Samples with a Calix[4]arene Modified Carbon Paste Electrode by Differential Pulse Anodic Stripping Voltammetry

A calix[4]arene modified carbon paste electrode was used for trace determination of copper. The study of the preconcentration of copper as well as the other heavy metal ions at the modified electrode, with subsequent measurement by differential pulse anodic stripping voltammetry (DPASV), indicates the efficient open‐circuit accumulation of the analytes onto the electrode. Many parameters such as the composition of the paste, pH, preconcentration time and stirring rate influence the response of the measurement. The procedure was optimized for copper determination. For a 10‐minute preconcentration time at pH 6.5–7.5, the detection limit (LOD) was 1.1 μg L^?1. The optimized method was successfully applied to the determination of copper in tap water sample by means of standard addition procedure. The copper content of the sample was comparable with the result obtained with AAS method.