Voltammetric copper(II) determination with a montmorillonite-modified carbon paste electrode

The clay mineral montmorillonite has been tested as modifier for the carbon paste electrode with a novel electrode modification technique. The differential pulse voltammetric determination of copper(II) by means of this modified carbon paste electrode has been studied. A detection limit of 4x10(-8) mol/l has been achieved after 10 min preconcentration under open circuit conditions with subsequent anodic stripping voltammetry. The calibration curve for Cu(II) is linear in the range of 4x10(-8)-8x10(-7) mol/l. Pb interferes in a 10-fold molar and Cd and Hg in a 100-fold molar excess. The interference by humic ligands is significant.     

Voltammetric copper(II) determination with a montmorillonite-modified carbon paste electrode

The clay mineral montmorillonite has been tested as modifier for the carbon paste electrode with a novel electrode modification technique. The differential pulse voltammetric determination of copper(II) by means of this modified carbon paste electrode has been studied. A detection limit of 4×10^-8 mol/l has been achieved after 10 min preconcentration under open circuit conditions with subsequent anodic stripping voltammetry. The calibration curve for Cu(II) is linear in the range of 4×10^-8–8×10^-7 mol/l. Pb interferes in a 10-fold molar and Cd and Hg in a 100-fold molar excess. The interference by humic ligands is significant.     

Hg(II) immobilized MWCNT graphite electrode for the anodic stripping voltammetric determination of lead and cadmium

The preparation of Hg(II)-modified multi walled carbon nanotube (MWCNT) by reaction of oxidized MWCNT with aqueous HgCl₂ was carried out. The Hg(II)-modified multi walled carbon nanotube (Hg(II)/MWCNT) dispersed in Nafion solution was used to coat the polished graphite electrode surface. The Hg(II)/MWCNT modified graphite electrode was held at a cathodic potential (−1.0 V) to reduce the coordinated Hg(II) to Hg forming nanodroplets of Hg. The modified electrode was characterized by FESEM/EDAX which provided useful insights on the morphology of the electrode. The SEM images showed droplets of Hg in the size of around 260 nm uniformly distributed on the MWCNT. Differential pulse anodic stripping voltammetry (DPASV) and electrochemical impedance spectroscopy were used to study the Hg(II) binding with MWCNT. Differential pulse anodic stripping voltammetry of ppb levels of cadmium and lead using the modified electrode yielded well-defined peaks with low background current under a short deposition time. Detection limit of 0.94 and 1.8 ng L⁻¹ were obtained following a 3 min deposition for Pb(II) and Cd(II), respectively. Various experimental parameters were characterized and optimized. High reproducibility was observed from the RSD values for 20 repetitive measurements of Pb(II) and Cd(II) (1.7 and 1.9%, respectively). The determination of Pb(II) and Cd(II) in tap water and Pb(II) in human hair samples was carried out. The above method of fabrication of Hg(II)/MWCNT modified graphite electrode clearly suggests a safe route for preparing Hg immobilized electrode for stripping analysis.     

Trace Analysis of Heavy Metals (Cd,Pb, Hg) Using Native and Modified 3D Printed Graphene/Poly(Lactic Acid) Composite Electrodes

Here we investigate the use of 3D printed graphene/poly(lactic acid) (PLA) electrodes for quantifying trace amounts of Hg, Pb, and Cd. We prepared cylindrical electrodes by sealing a 600 μm diameter graphene/PLA filament in a pipette tip filled with epoxy. We characterized the electrodes using scanning electron microscopy, Raman spectroscopy, and cyclic voltammetry in ferrocene methanol. The physical characterization showed a significant amount of disorder in the carbon structure and the electrochemical characterization showed quasi‐reversible behavior without any electrode pretreatment. We then used unmodified graphene/PLA electrode to quantify Hg, and Pb and Cd in 0.01 M HCl and 0.1 M acetate buffer using square wave anodic stripping voltammetry. We were able to quantify Hg with a limit of detection (LOD) of 6.1 nM (1.2 ppb), but Pb and Cd did not present measurable peaks at concentrations below ～400 nM. We improved the LODs for Pb and Cd by depositing Bi microparticles on the graphene/PLA and, after optimization, achieved clear stripping peaks at the 20 nM level for both ions (4.1 and 2.2 ppb for Pb²⁺ and Cd²⁺, respectively). The results obtained for all three metals allowed quantification below the US Environmental Protection Agency action limits in drinking water.     

Simultaneous detection of cadmium, copper, and lead using a carbon paste electrode modified with carbamoylphosphonic acid self-assembled monolayer on mesoporous silica (SAMMS)

A new sensor was developed for simultaneous detection of cadmium (Cd²⁺), copper (Cu²⁺), and lead (Pb²⁺), based on the voltammetric response at a carbon paste electrode modified with carbamoylphosphonic acid (acetamide phosphonic acid) self-assembled monolayer (SAM) on mesoporous silica (Ac-Phos SAMMS). The adsorptive stripping voltammetry (AdSV) technique involves preconcentration of the metal ions onto Ac-Phos SAMMS under an open circuit, then electrolysis of the preconcentrated species, followed by a square wave potential sweep towards positive values. Factors affecting the preconcentration process were investigated. The voltammetric responses increased linearly with the preconcentration time from 1 to 30 min or with metal ion concentrations ranging from 10 to 200 ppb. The responses also evolved in the same fashion as adsorption isotherm in the pH range of 2-6. The metal detection limits were 10 ppb after 2 min preconcentration and improved to 0.5 ppb after 20 min preconcentration.     

Stripping voltammetric determination of mercury(II) at antimony-coated carbon paste electrode

A new procedure was elaborated to determine mercury(II) using an anodic stripping square-wave voltammetry at the antimony film carbon paste electrode (SbF-CPE). In highly acidic medium of 1 M hydrochloric acid, voltammetric measurements can be realized in a wide potential window. Presence of cadmium(II) allows to separate peaks of Hg(II) and Sb(III) and apparently catalyses reoxidation of electrolytically accumulated mercury, thus allowing its determination at ppb levels. Calibration dependence was linear up to 100 ppb Hg with a detection limit of 1.3 ppb. Applicability of the method was tested on the real river water sample.     

Simultaneous trace-levels determination of Hg(II) and Pb(II) ions in various samples using a modified carbon paste electrode based on multi-walled carbon nanotubes and a new synthesized Schiff base

A modified carbon paste electrode based on multi-walled carbon nanotubes (MWCNTs) and 3-(4-methoxybenzylideneamino)-2-thioxothiazolodin-4-one as a new synthesized Schiff base was constructed for the simultaneous determination of trace amounts of Hg(II) and Pb(II) by square wave anodic stripping voltammetry. The modified electrode showed an excellent selectivity and stability for Hg(II) and Pb(II) determinations and for accelerated electron transfer between the electrode and the analytes. The electrochemical properties and applications of the modified electrode were studied. Operational parameters such as pH, deposition potential and deposition time were optimized for the purpose of determination of traces of metal ions at pH 3.0. Under optimal conditions the limits of detection, based on three times the background noise, were 9.0 × 10⁻⁴ and 6.0 × 10⁻⁴ μmol L⁻¹ for Hg(II) and Pb(II) with a 90 s preconcentration, respectively. In addition, the modified electrode displayed a good reproducibility and selectivity, making it suitable for the simultaneous determination of Hg(II) and Pb(II) in real samples such as sea water, waste water, tobacco, marine and human teeth samples.     

Voltammetric analysis of Pb(II) in natural waters using a carbon paste electrode modified with 5-mercapto-1-methyltetrazol grafted on hexagonal mesoporous silica

A hexagonal mesoporous silica (HMS) functionalized with a 5-mercapto-1-methyltetrazole derivative was employed to prepare a chemically modified carbon paste electrode for Pb(II) detection in aqueous solution by square wave adsorptive stripping voltammetry. The optimal operating conditions were 5 min preconcentration time at pH 6.5, and 120 s electrolysis time in 0.2 mol L^?1 HCl. Under these conditions, the voltammetric signal increased linearly with the preconcentration time in the range 1 to 10 min and with the Pb(II) concentration in the range 1 to 100?µg L^?1. The electrode was reproducible and sensitive. Simultaneous determination of Pb, Cd and Cu was also carried out with the electrode. The accuracy of the method was validated by analysing Pb(II) in tap water and groundwater samples.     

Water hyacinth modified carbon paste electrode for simultaneous electrochemical stripping analysis of Cd (II) and Pb (II)

In this study, we demonstrated a highly sensitive electrochemical sensor for the simultaneous detection of Pb (II) and Cd (II) in aqueous solution using carbon paste electrode modified with Eichhornia crassipes powder by square wave anodic stripping voltammetry. The effect of modifier composition, pH, preconcentration time, reduction potential and time, and type of supporting electrolyte on the determination of metal ions were investigated. Pre-concentration on the modified surface was performed at open circuit. The modified electrode exhibited well-defined and separate stripping peaks for Pb (II) and Cd (II). Under optimum experimental conditions, a linear range for both metal ions was from 10 to 5000 μg L^?1 with the detection limits of 4.9 μg L^?1, 2.1 μg L^?1 for Cd(II) and Pb (II), respectively. The modified electrode was found to be sensitive and selective when applied to determine trace amounts of Cd (II) and Pb (II) in natural water samples.     

Stripping Voltammetry of Mercury(II) with a Chemically Modified Carbon Paste Electrode Containing Silica Gel Functionalized with 2,5‐Dimercapto‐1,3,4‐thiadiazole

The accumulation voltammetry of mercury(II) was investigated at a carbon paste electrode chemically modified with silica gel functionalized with 2,5‐dimercapto‐1,3,4‐thiadiazole (DTTPSG‐CPE). The repetitive cyclic voltammogram of mercury(II) solution in the potential range ?0.2 to +0.8 V (vs. Ag/AgCl), (0.02 mol L^?1 KNO₃ ; v=20 mV s^?1) show two peaks one at about 0.0 V and other at 0.31 V. However, the cathodic wave peak, around 0.0 V, is irregular and changes its form in each cycle. This peak at about 0.0 V is the reduction current for mercury(II) accumulated in the DTTPSG‐CPE. The anodic wave peak at 0.31 V is well‐defined and does not change during the cycles. The resultant material was characterized by cyclic and differential pulse anodic stripping voltammetry performed with the electrode in differents supporting electrolytes. The mercury response was evaluated with respect to pH, electrode composition, preconcentration time, mercury concentration, “cleaning” solution, possible interferences and other variables. The precision for six determinations (n=6) of 0.05 and 0.20 mg L^?1 Hg(II) was 2.8 and 2.2% (relative standard deviation), respectively. The method was satisfactory and used to determine the concentration of mercury(II) in natural waters contaminated by this metal.     

Synthesis and application of a natural-based nanocomposite with carbon nanotubes for sensitive voltammetric determination of lead (II) ions

ABSTRACT

A modified carbon paste electrode has been developed for the determination of Pb(ΙΙ) ions based on Fe₃O₄/eggshell magnetic nanocomposite. The structure and morphology of Fe₃O₄/eggshell were analysed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The prepared nanocomposite was also characterized by Fourier transform infrared spectroscopy (FT-IR) and vibrating sample magnetometer (VSM). The electrochemical procedure was based on the accumulation and determination of Pb(ΙΙ) ions at the surface of the modified carbon paste electrode with Fe₃O₄/eggshell nanocomposites and carbon nanotubes by differential pulse anodic stripping voltammetry (DPASV). Various experimental parameters involved in the preconcentration of Pb(ΙΙ) ions and voltammetric stripping step were studied. Under the optimum conditions, the voltammetric peak current of Pb(ΙΙ) occurs at a potential about ?0.5 V. Also, the voltammetric peak current increased linearly with Pb(ΙΙ) concentration in the range of 0.5–200 ng mL^?1 and a detection limit of 0.15 ng mL^?1 was obtained for Pb(ΙΙ). The selectivity of the proposed electrode for Pb(ΙΙ) ions in the presence of some cations was also examined. The practical application of the proposed modified electrode was evaluated by the determination of Pb(ΙΙ) ions in human hair and water samples. The results were satisfactory for the spiked samples.     

A new method for the voltammetric determination of molybdenum(VI) using carbon paste electrodes modified in situ with cetyltrimethylammonium bromide

Molybdenum(VI) is determined by anodic stripping voltammetry using a carbon paste electrode modified in situ with cetyltrimethylammonium bromide (CTAB). The preconcentration of molybdenum is performed by adsorption and reduction of ion-pairs of cetyltrimethylammonium and molybdenum(VI) oxalate at a potential of −0.4 V vs. the saturated calomel electrode (SCE). The supporting electrolyte contains 0.01 M oxalic acid and 0.075 mM CTAB. Differential pulse anodic stripping voltammetry exploiting the reoxidation signal is used for the determination of trace levels of molybdenum(VI). Linearity between current and concentration exists for a range of 0.5–500 μg 1⁻¹ Mo with proper preconcentration times; the limit of detection (calculated as 3σ) is 0.04 μg 1⁻¹ with an accumulation period of 10 min.     

Polyviologen Modified Glassy Carbon Electrode Employed for Anodic Stripping Voltammetric Determination of Mercury(II)

In this study, a polyviologen modified glassy carbon electrode (PVGCE) was used to detect Hg(II) in aqueous solutions containing significant amounts of chloride anions in order to demonstrate the electroanalytical application of the electropolymerized polyviologen. The polyviologen thin film was formed on the electrode surface by applying a constant potential of ?1.0 V in the pH 4.2 Britton–Robinson (BR) buffer solution that contains 0.1 wt% of viologen oligomers. The PVGCE was found capability to improve the detection limit of Hg(II) in the solutions with high concentration of chloride because Hg(II) forms negative complex ions HgCl that can be accumulated to PVGCE by the anion‐exchange characteristic of polyviologen. With 5 minutes accumulation at ?0.2 V, the adsorbed HgCl anions were reduced to Hg and deposited on the electrode surface, and were determined with the following anodic stripping differential pulse voltammetry (ASDPV). The dependence of anodic stripping current versus concentration was linear from 1 ppb (5 nM) to 100 ppb (0.5 μM) with a regression coefficient of 0.9959.     

Anodic stripping voltammetric determination of bismuth(III) using a Tosflex-coated mercury film electrode

A Tosflex-mercury film electrode (TMFE) was prepared by spin-coating a solution of the perfluorinated anion exchange polymer Tosflex onto a glassy carbon electrode surface followed by electrodeposition of mercury film on this electrode. This electrode was used for the determination of trace bismuth(III) which was preconcentrated onto the TMFE as anionic bismuth(III) complexes with chloride in a chloride medium. The preconcentration was carried out at a potential of-0.2 V, and the preconcentration of the bismuth(III) was enhanced significantly by the anion-exchange feature of Tosflex. The accumulated bismuth(III) was then determined by anodic square-wave stripping voltammetry (SWSV). Various parameters influencing the determination of bismuth(III) were examined in detail. With 2 min accumulation, the analytical signal versus concentration dependence was linear up to 50 ppb, and the detection limit was 0.58 ppb. This modified electrode showed good resistance to the interferences from surface-active compounds and common ions.     

Fullerene-based anodic stripping voltammetry for simultaneous determination of Hg(II), Cu(II), Pb(II) and Cd(II) in foodstuff

Various carbon nanomaterials for use in anodic stripping voltammetric analysis of Hg(II), Cu(II), Pb(II) and Cd(II) are screened. Graphene, carbon nanotubes, carbon nanofibers and fullerene (C₆₀), dispersed in chitosan (Chit) aqueous solution, are used to modify a glassy carbon electrode (GCE). The fullerene-chitosan modified GCE (C₆₀-Chit/GCE) displays superior performance in terms of simultaneous determination of the above ions. The electrodes and materials are characterized by electrochemical impedance spectroscopy, cyclic voltammetry, scanning electron microscopy, Raman spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The excellent performance of C₆₀-Chit/GCE is attributed to the good electrical conductivity, large surface area, strong adsorption affinity and unique crystalline structure of C₆₀. Using differential pulse anodic stripping voltammetry, the assay has the following features for Hg(II), Cu(II), Pb(II) and Cd(II), respectively: (a) Peak voltages of +0.14, ?0.11, ?0.58 and???0.82 V (vs SCE); (b) linear ranges extending from 0.01–6.0 μM, 0.05–6.0 μM, 0.005–6.0 μM and 0.5–9.0 μM; and (c), detection limits (3σ method) of 3 nM (0.6 ppb), 14 nM (0.9 ppb), 1 nM (0.2 ppb) and 21 nM (2.4 ppb). Moreover, the modified GCE is well reproducible and suitable for long-term usage. The method was successfully applied to the simultaneous determination of these ions in spiked foodstuff.

Open image in new window

Graphical abstract Compared with graphene, carbon nanotubes and carbon nanofibers, an electrode modified with fullerene in chitosan electrode displays superior performance for the simultaneous anodic stripping voltammetric detection of Hg(II), Cu(II), Pb(II) and Cd(II).

     

Differential pulse anodic stripping voltammetric determination of lead(II) with a 1,4-bis(prop-2'-enyloxy)-9,10-anthraquinone modified carbon paste electrode

A sensitive and selective method for the determination of lead(II) with a 1,4-bis(prop-2'-enyloxy)-9,10-anthraquinone (AQ) modified carbon paste electrode has been developed. The method is based on non-electrolytic preconcentration via complex formation with modifier, followed by an accumulation period with a negative potential (-1.5 V), and then by a proper anodic stripping. The analytical performance was evaluated with respect to the quantity of modifier in the paste, concentration of electrolyte solution, preconcentration time, lead(II) concentration, and other variables. A linear calibration graph was obtained in the concentration range 2.00x10(-9)-1.06x10(-5) M Pb(II) (n=21, r=0.9999) with 30 s preconcentration time. The detection limit was found to be 1x10(-9) M. For eight preconcentration/determination cycles, the differential pulse voltammetric response was reproduced with 5.0 and 3.7% relative standard deviations at 2.00x10(-8) and 2.00x10(-6) M Pb(II), respectively. Rapid and convenient renewal of electrode surface allows the use of a single modified electrode surface in multiple analytical determinations over several weeks. Many coexisting metal ions had little or no effect on the determination of lead(II). The developed method was applied to lead determination in waste waters.     

Preconcentration and determination of mercury(II) at a chemically modified electrode containing 3-(2-thioimidazolyl)propyl silica gel.

A mercury-sensitive chemically modified graphite paste electrode was constructed by incorporating modified silica gel into a conventional graphite paste electrode. The functional group attached to the (3-chloropropyl) silica gel surface was 2-mercaptoimidazole, giving a new product denoted by 3-(2-thioimidazolyl)propyl silica gel, which is able to complex mercury ions. Mercury was chemically adsorbed on the modified graphite paste electrode containing 3-(2-thioimidazolyl)propyl silica (TIPSG GPE) by immersion in a Hg(II) solution, and the resultant surface was characterized by cyclic and differential pulse anodic stripping voltammetry. One cathodic peak at 0.1 V and other anodic peak at 0.34 V were observed on scanning the potential from -0.1 to 0.8 V (0.01 M KNO3; v = 2.0 mV s(-1) vs. Ag/AgCl). The anodic peak at 0.34 V show an excellent sensitivity for Hg(II) ions in the presence of several foreign ions. A calibration graph covering the concentration range from 0.02 to 2 mg L(-1) was obtained. The detection limit was estimated to be 5 microg L(-1). The precision for six determinations of 0.05 and 0.26 mg L(-1) Hg(II) was 3.0 and 2.5% (relative standard deviation), respectively. The method can be used to determine the concentration of mercury(II) in natural waters contaminated by this metal.     

Preparation of a clay-modified carbon paste electrode based on 2-thiazoline-2-thiol-hexadecylammonium sorption for the sensitive determination of mercury.

A montmorillonite from Wyoming-USA was used to prepare an organo-clay complex, named 2-thiazoline-2-thiol-hexadecyltrimethylammonium-clay (TZT-HDTA-clay), for the purpose of the selective adsorption of the heavy metals ions and possible use as a chemically modified carbon paste electrode (CMCPE). Adsorption isotherms of Hg2+, Pb2+, Cd2+, Cu2+, and Zn2+ from aqueous solutions as a function of the pH were studied at 298 K. Conditions for quantitative retention and elution were established for each metal by batch and column methods. The organo-clay complex was very selective to Hg(II) in aqueous solution in which other metals and ions were also present. The accumulation voltammetry of Hg(II) was studied at a carbon paste electrode chemically modified with this material. The mercury response was evaluated with respect to the pH, electrode composition, preconcentration time, mercury concentration, "cleaning" solution, possible interferences and other variables. A carbon paste electrode modified by TZT-HDTA-clay showed two peaks: one cathodic peak at about 0.0 V and an anodic peak at 0.25 V, scanning the potential from -0.2 to 0.8 V (0.05 M KNO3 vs. Ag/AgCl). The anodic peak at 0.25 V presents excellent selectivity for Hg(II) ions in the presence of foreign ions. The detection limit was estimated as 0.1 microg L(-1). The precision of determination was satisfactory for the respective concentration level.     

Coal as a New Carbon Paste Electrode Modifier with Sorption Properties

A new type of carbon paste electrode modified with subbituminous and bituminous coal is presented. The operability of the coal carbon paste electrode with respect to the working potential window attainable was tested in various electrolytes. Cyclic voltammetry of the reference redox system [Fe(CN)₆]^3?/4? was performed to evaluate electron transfer kinetics. Open‐circuit sorption of Cd(II), Pb(II), and Cu(II) with subsequent anodic stripping voltammetry was used to pilot coal sorption ability. The coal modified carbon paste electrode was also examined as a support for mercury film deposition and anodic stripping voltammetry of metals.     

Application of Novel Zn‐Ferrite Modified Glassy Carbon Paste Electrode as a Sensor for Determination of Cd(II) in Waste Water

This paper describes the preparation of a new sensor based on Zn‐ferrite modified glassy carbon paste electrode and its electrochemical application for the determination of trace Cd(II) ions in waste waters using differential pulse anodic stripping voltammetry (DPASV). Different Zn/Ni ferrite nanoparticles were synthesized and characterized using scanning electron microscopy (SEM) and X‐ray powder diffraction (XRPD). The prepared ferrite nanoparticles were used for the preparation of Zn‐ferrite‐modified glassy carbon paste electrode (ZnMGCPE) for determination of Cd(II) at nanomolar levels in waste water at pH 5. The different parameters such as conditions of preparation, Zn²⁺/Ni²⁺/Fe²⁺ ratio and electrochemical parameters, percentage of modifier, accumulation time, pH and accumulation potential were investigated. Besides, interference measurements were also evaluated under optimized parameters. The best voltammetric response was observed for ZnFe₂O₄ modifier, when the percentage of modifier was 3 %, accumulation time 9 min, pH of supporting electrolyte 5 and accumulation potential ?1.05 V. Thus prepared electrode displays excellent response to Cd(II) with a detection limit of 0.38 ppb, and selective detection toward Cd(II) was achieved.