Simultaneous and Sensitive Detection of Cd(II) and Pb(II) Using a Novel Bismuth Film/Ordered Mesoporous Carbon‐molecular Wire Modified Graphite Carbon Paste Electrode

An electrochemical sensor for the simultaneous and sensitive detection of Cd(II) and Pb(II) is proposed on the basis of square‐wave anodic stripping voltammetry (SWASV) experiments using a novel bismuth film/ordered mesoporous carbon‐molecular wire modified graphite carbon paste electrode (Bi/OMC‐MW/GCPE). Ordered mesoporous carbon (OMC) and molecular wire (MW) (diphenylacetylene) were used as the modifier and binder, respectively. The Bi/OMC‐MW/GCPE was prepared with the addition of graphite powder, OMC and DPA at the ratio of 2 : 1 : 1. The electrochemical properties and morphology of the electrode were characterized by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), SWASV and scanning electron microscopy (SEM). The parameters affecting the stripping current response were investigated and optimized. The experimental results show that the prepared electrode exhibited excellent electrochemical performance, good electrical conductivity and a high stripping voltammetric response. Under optimized conditions, a linear range was achieved over a concentration range from 1.0 to 70.0 μg/L for both Cd(II) and Pb(II) metal ions, with detection limits of 0.07 μg/L for Cd(II) and 0.08 μg/L for Pb(II) (S/N=3) with the deposition time 150 s. Moreover, the sensor exhibited improved sensitivity and reproducibility compared to traditional CPEs. The fabricated electrode was then successfully used to satisfactorily detect Cd(II) and Pb(II) in real soil samples.     

Disposable screen-printed bismuth electrode modified with multi-walled carbon nanotubes for electrochemical stripping measurements

Integrating the advantages of screen printing technology with the encouraging electroanalytical characteristic of metallic bismuth, we developed an ultrasensitive and disposable screen-printed bismuth electrode (SPBE) modified with multi-walled carbon nanotubes (MWCNTs) for electrochemical stripping measurements. Metallic bismuth powders and MWCNTs were homogeneously mixed with graphite-carbon ink to mass-prepare screen-printed bismuth electrode doped with multi-walled carbon nanotubes (SPBE/MWCNT). The electroanalytical performance of the prepared SPBE/MWCNT was intensively evaluated by measuring trace Hg(II) with square-wave anodic stripping voltammetry (SWASV). The results indicated that the SPBE modified with 2 wt% MWCNTs could offer a more sensitive response to trace Hg(II) than the bare SPBE. The stripping current obtained at SPBE/MWCNT was linear with Hg(II) concentration in the range from 0.2 to 40 μg/L (R(2) = 0.9976), with a detection limit of 0.09 μg/L (S/N = 3) under 180 s accumulation. The proposed "mercury-free" electrode, with extremely simple preparation and ultrahigh sensitivity, holds wide application prospects in both environmental and industrial monitoring.     

Disposable Screen-Printed Electrodes (Spe) Mercury-Free for Lead Detection

ABSTRACT

Strategies to modify screen-printed electrodes (SPE) for lead determination are reported. Dithizone was mixed with graphite ink to obtain a modified screen-printed strip to detect ppb levels of lead(II) (detection limit 12 μg/l) using square wave anodic stripping voltammetry (SWASV). In addition, screen-printed electrodes were also modified by casting a few μl of a Nafion® solution onto the working electrode surface. In this case, ppb levels of lead were detected (detection limit 15 μg/1), using potentiometric stripping analysis (PSA). The addition of an ionophore to Nafion® polymer was also investigated, but this did not yield a significant improvement.     

Electroanalytical Determination of Cd(II) and Pb(II) in Bivalve Mollusks using Electrochemically Reduced Graphene Oxide‐based Electrode

An electrochemical sensor for the simultaneous determination of Cd(II) and Pb(II) by square wave anodic stripping voltammetry (SWASV) in bivalve mollusks using a glassy carbon electrode modified with electrochemically reduced graphene oxide has been developed. The modified surface was characterized by cyclic voltammetry, high resolution scanning electron microscopy (HR‐SEM), and Raman spectroscopy. The optimum conditions were optimized and a linear range was observed from 15–105 μg L^?1 with a limits of detection of 15 μg L^?1 for Cd(II) and Pb(II). The methodology was validated and applied in different samples of commercial bivalve mollusks with satisfactory results. The high conductivity and greater surface area of the modifying agent improves the preconcentration capacity of the electrochemical sensor, allowing to develop a simple, rapid and sensitive analysis in the detection of lead and cadmium in marine resources.     

Improvement of an Enzyme Immunoassay for the Determination of Mercury(II)

Three systems were tested for the optimization of a heterogenous non-competitive enzyme immunoassay (EIA) for the determination of Hg (II). The sensitivity of the non optimized Hg-EIA with a detection limit of 2.1 μg/L Hg (II) was improved by an avidin-biotin-complex (ABC) amplification system to a 2-fold lower detection limit (1.1 μg/L Hg (II)). A conventional competitive ElA with the competition reaction between bound and free Hg (II) for antibody (ab) binding sites yielded a detection limit of 1.0 μg/L Hg (II). Further improvement of sensitivity could be achieved by a competitive displacement EIA. In this case ab molecules bound to immobilized haptens are displaced in the next step by free Hg (II). The detection limit of the displacement approach is 0.4 μg/L Hg (II).     

Microliter Volume Determination of Cosmetic Mercury with a Partially Crosslinked Poly(4‐vinylpyridine) Modified Screen‐Printed Three‐Electrode Portable Assembly

We successfully demonstrated microliter (μL) volume determination of Mercury (Hg) using an in‐built screen‐printed three electrodes containing partially crosslinked poly(4‐vinlylpyridine) (designated as pcPVP) modified carbon‐working, carbon‐counter, and Ag⁺‐quasireference electrodes (SPE/pcPVP) in a pH 4 acetate buffer solution with 2 M KCl by using the square wave anodic stripping voltammetric (SWASV) technique. Instrumental and solution phase conditions were systematically optimized. Experiments were carried out by simply placing a 500 μL‐droplet of Hg containing real sample mixed with the base electrolyte on the SPE/pcPVP surface. The SPE/Ag⁺ quasi‐reference system shifted the Hg‐SWASV detection potential ca. 250 mV positive, but the quantitative current values were appreciably similar to that of a standard Ag/AgCl reference electrode. Under optimal condition, the calibration graph is linear in the window of 100–1000 ppb of the Hg droplet system with a detection limit of 69.5 ppb (S/N=3). Finally real sample assays were demonstrated for prohibited cosmetic Hg containing skin‐lightening agents in parallel with ICP‐OES measurements.     

Differential Pulse Anodic Stripping Voltammetric Determination of Lead (II) Using Poly Xylenol Orange Modified Electrode

In this work a method for sensitive anodic stripping voltammetric determination of Pb(II) ions using a poly xylenol orange film modified electrode (PXOFME) has been proposed. Poly xylenol orange film (PXOF) was formed on a paraffin impegrenated graphite electrode (PIGE) using electro polymerization method by scanning the potential between −0.5 V to 1.3 V, at a scan rate of 50 mV/s for 30 segments in 0.1 M phosphate buffer solution (PBS) of pH 7. The PXOFME was characterized by scanning electron microscopy (SEM), ATR‐IR spectroscopy, cyclic voltammetry (CV), differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS). The modified electrode has been used to develop a sensitive method for the determination of Pb(II) ions by anodic stripping voltmmetry (ASV). The PXOFME was used to preconcentrate Pb(II) ions through complexation, the complexed metal ions were reduced electrochemically and then stripped anodically from the surface of the electrode. A linear range of 5 μg/L to 413 μg/L with a limit of detection (S/N=3) of 1.6 μg/L was observed for the determination of Pb(II) ions. The method was applied to lead determination in sea water and tap water samples and the results were found to be satisfactory.     

Novel Three-dimensional Sensor for Rapid Detection of Pb(II) and Cd(II) in Edible Mushrooms

A sensing platform was developed based on the molybdenum disulfide-reduced graphene oxide (MoS₂-RGO). The flower-like MoS₂-RGO nanocomposite had a large number of active sites such as oxygen-containing groups and highly reactive sulfur that contributed to the adsorption and preconcentration of heavy metal ions (HMIs). MoS₂-RGO was synthesized by one-step reduction method. Under optimized conditions, the limits of detection (LODs) for Pb(II) and Cd(II) was 0.13 μg/L and 0.59 μg/L with a linear range of 4.1–207.2 μg/L and 2.2–112.4 μg/L, respectively. The modified sensors had been successfully applied to detect Pb(II) and Cd(II) in three kinds of edible mushrooms.     

Performance of a Bismuth Bulk Rotating Disk Electrode for Heavy Metal Analysis: Determination of Lead in Environmental Samples

The bismuth bulk electrode is proposed here for the first time in the rotating configuration (BiB‐RDE) as the electrode of choice for voltammetric analysis of selected heavy metal ions. Optimization of chemical and instrumental parameters was carried out to develop a reliable and convenient method for the determination of Zn(II), Cd(II) and Pb(II) by SWASV. Appropriate detection limits were found for environmental monitoring applications in the medium – low µg/L range. The method was validated for Pb(II) determination by certified reference materials. Successful application to the determination of Pb(II) in samples of fortified rainwater and sewage sludge from a steel industry is described.     

AgNP/Bi/Nafion‐modified Disposable Electrodes for Sensitive Zn(II), Cd(II), and Pb(II) Detection in Aerosol Samples

A new method for modifying electrodes with Ag nanoparticles (AgNPs) using electrospray deposition for sensitive, selective detection of Zn(II), Cd(II), and Pb(II) in aerosol samples when combined with Bismuth and Nafion coating and square‐wave anodic stripping voltammetry (SWASV) is reported. Carbon stencil‐printed electrodes (CSPEs) fabricated on a polyethylene transparency (PET) sheet were produced for an inexpensive, simple to fabricate, disposable sensor that can be used with the microliter sample volumes for analysis. Sensor performance was improved by modifying the electrode surface with electrospray‐deposited AgNPs. The use of electrospray deposition resulted in more uniform particle dispersion across the electrode surface when compared to drop‐casting. Using AgNP‐modified electrodes combined with Bi and Nafion, experimental detection limits (LODs) of 5.0, 0.5, and 0.1 μg L⁻¹ for Zn(II), Cd(II), and Pb(II), respectively, were achieved. The linear working ranges were 5.0–400.0 μg L⁻¹, 0.5–400.0 μg L⁻¹, and 0.1–500.0 μg L⁻¹ for Zn(II), Cd(II), and Pb(II), respectively. Interference studies showed Cu(II) was the only metal that interfered with this assay but inference could be eliminated with the addition of ferricyanide directly to the sample solution. This electrochemical sensor was applied for the simultaneous determination of Zn(II), Cd(II), and Pb(II) within source particulate matter (PM) samples collected on filters using an aerosol test chamber.     

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).     

Electrothermal Atomic Absorption Spectrometric Determination of Cobalt,Copper and Nickel in Fresh Water After Their Preconcentration by Precipitate Flotation

Abstract

A method is developed for simultaneous separation and determination of μg/L levels of Co(II), Cu(II) and Ni(II) in fresh water by precipitate flotation. The optimal conditions of the experimental procedure with hydrated iron(III) oxide and iron(III) tetramethylenedithiocarbamate as collectors were investigated. The pH interval of the working medium, within which Co(II), Cu(II) and Ni(II) can be successfully separated, was determined from the aspect of collectors and surfactant stability. The amounts of the elements investigated were determined by electrothermal atomic absorption spectrometry. The detection limit of the method is 0.15 μg/L for cobalt, 0.03 μg/L for copper and 0.79 μg/L for nickel.     

Ultrasensitive Voltammetric Detection of Trace Lead(II) and Cadmium(II) Using MWCNTs‐Nafion/Bismuth Composite Electrodes

Multiwall carbon nanotubes were dispersed in Nafion (MWCNTs‐NA) solution and used in combination with bismuth (MWCNTs‐NA/Bi) for fabricating composite sensors to determine trace Pb(II) and Cd(II) by differential pulse anodic stripping voltammetry (DPASV). The electrochemical properties of the MWCNTs‐NA/Bi composites film modified glassy carbon electrode (GCE) were evaluated. The synergistic effect of MWCNTs and bismuth composite film was obtained for Pb(II) and Cd(II) detection with improved sensitivity and reproducibility. Linear calibration curves ranged from 0.05 to 100 μg/L for Pb(II) and 0.08 to 100 μg/L for Cd(II). The determination limits (S/N=3) were 25 ng/L for Pb and 40 ng/L for Cd, which compared favorably with previously reported methods in the area of electrochemical Pb(II) and Cd(II) detection. The MWCNTs‐NA/Bi composite film electrodes were successfully applied to determine Pb(II) and Cd(II) in real sample, and the results of the present method agreed well with those of atomic absorption spectroscopy.     

Single-use optical sensor for the determination of iron in water and white wines

A new method, based on the use of a disposable sensor, for the determination of Fe(II) in waters and wines is proposed. The sensor is formed by an inert rectangular strip of polyester (Mylar) and a circular film (6 mm in diameter) adhered on its surface. This film, which contains the required reagents for the fixation of the analyte by means of a complexation reaction, forms the sensing zone of the sensor. When the sensor is introduced in an acidified (pH 2.5) sample solution containing between 4.0 and 300.0 μg/L of Fe(II), a violet-red colour develops in the initially colourless sensing zone. The linear range of the method depends of the equilibration time of the sensor with the sample solution. Thus, when the equilibration time was 5 min, the linear range was 41.0–300.0 μg/L, while for 60 min the range was 4.0– 50.0 μg/L. Detection and quantification limits were 12.0 and 41.0 μg/L, respectively, for an equilibration time of 5 min. The precision of the method, expressed as relative standard deviation of ten samples of 100.0 μg/L of Fe(II), was 4.9%. Interferences produced by other species usually present in waters or wines have been studied. Cu(II) and Co(II) interfered seriously at concentration levels higher than 100.0 and 150.0 μg/L, respectively. The method was applied to the determination of Fe(II) in different types of waters and wines, using atomic absorption spectrometry as a reference method.     

Long‐life Heavy Metal Ions Sensor Based on Graphene Oxide‐anchored Conducting Polymer

A long‐life electrochemical sensor for the continuous analysis of heavy metal ions (Zn(II), Cd(II), Pb(II), Cu(II), and Hg(II)) was developed using the graphene oxide (GO) anchored‐functionalized polyterthiophene (poly[3′‐(2‐aminopyrimidyl)‐2,2′:5′,2′′‐terthiophene], polyPATT) composite. The PATT monomer was synthesized and polymerized with GO to form the composite using a potential cycling method, followed by Nafion coating. The modified sensor surface was characterized employing electrochemical and surface analysis methods. Experimental variables affecting the analytical performance were optimized. Interference effects of other metal ions having similar redox potentials were also investigated. The performance of chronocoulometry (CC) without predeposition was compared with the results of square wave anodic stripping voltammetry (SWASV) with predeposition. The dynamic range of CC for the target ions were between 1 ppb and 10 ppm, respectively with the detection limits between 0.05 (±0.05) and 0.20 (±0.15) ppb for the CC method without predeposition, and between 0.08 (±0.05) and 0.30 (±0.12) ppb for the SWASV with 300 sec of deposition time (n=3 ). The reliability of the method was evaluated by continuously analysing environmental water samples using a single sensor probe in a flow system for 93 days.     

Indirect Determination of Trace Copper(II) by Adsorptive Stripping Voltammetry with Zincon at a Carbon Paste Electrode

Traces of copper(II) can be determined by adsorptive stripping voltammetry using 2‐carboxy‐2′‐hydroxy‐5′‐sulfoformazyl benzene (Zincon) as complex forming reagent. First in phosphate buffer pH 6.4, copper(II)‐Zincon complex was adsorbed on carbon paste electrode (CPE) with an accumulation potential of 0.6 V. Following this, adsorbed complex was oxidized and detected by differential pulse voltammetric (DPV) scan from 0.6 to 1.0 V. The effective parameters in sensor response were examined. The detection limit (DL) of copper(II) was 1.1 μg/L and relative standard deviations (RSDs) for 10 and 200 μg/L Cu(II) were 1.81 and 1.03%, respectively. The calibration curve was linear for 2–220 μg/L copper(II). The resulting CPE does not use mercury and therefore, has a positive environmental benefit. The method, which is reasonably sensitive and selective, has been successfully applied to the determination of trace amount of copper in water and human hair samples.     

New sorbents and indicator powders for preconcentration and determination of trace metals in liquid samples

Two approaches to immobilize complex-forming analytical reagents (PAN, PAR, Xylenol orange, Brombenzothiazo, Crystal violet, Cadion, and Sulfochlorophenolazorhodanine) for the preparation of new sorbents and indicator powders are suggested: on-line coating of reversed-phase silica gel by reagents or doping of porous sol-gel silica with reagents. The retention of Ag, Cd, Cu(II), Co(II), Fe(III), Mn(II), Ni, Pb, and Zn on the sorbents developed was investigated. Quantitative sorption and desorption conditions were optimized. Procedures for the determination of Cd, Cu(II), Fe(III), Pb, and Zn with flame atomic absorption, spectrophotometric, and diffusion scattering spectrometric detection were elaborated. Detection limits for Cd, Cu(II), Fe(III), Pb, and Zn were 3 μg/L, 6 μg/L, 5 μg/L, 40 μg/L, and 1 μg/L, respectively. The procedures were used for the analysis of various real samples, e.g., natural and waste waters, and food.     

Novel Screen-Printed Gold Nano Film Electrode for Trace Mercury(II) Determination Using Anodic Stripping Voltammetry

Integrating the screen printing technique with the vacuum evaporation method, we developed a novel and disposable screen-printed gold film electrode (SPGFE) in the present work. First, a conductive silver layer, a connection graphite-carbon layer, and an insulating polymer layer were successively printed onto a flexible polyethylene terephthalate (PET) substrate. Then, a gold thin film was achieved on the scheduled vacant site by use of the vacuum evaporation method. In order to enhance the electroanalytical performance of the SPGFE, the thickness of the gold film was controlled in the range of 70–80 nm under optimum conditions. The fabricated SPGFE was applied to detect trace mercury(II) based on the square-wave anodic stripping voltammetry (SWASV). The results indicated that the proposed SPGFE exhibited higher sensitivity to trace mercury(II) than the gold disc electrode. The stripping current was linearly related to the concentration of mercury(II) in the range of 16–280 µg/L (R² = 0.9919) and 1.2–8.0 µg/L (R² = 0.9977), with a detection limit of 0.8 µg/L (S/N = 3) under 180 s accumulation. The SPGFE was further used to detect mercury in real samples, and the obtained results revealed a good agreement with those of inductively coupled plasma atomic emission spectrometry (ICP-AES) and atomic absorption spectroscopy (AAS). The highly sensitive and environmental friendly electrode, as another type of “mercury-free” electrode, holds great promise in stripping measurements.     

Graphene Oxide‐Modified Electrode Coated with in‐situ Antimony Film for the Simultaneous Determination of Heavy Metals by Sequential Injection‐Anodic Stripping Voltammetry

The proposed chemically modified electrode was graphene oxide that was synthesized via Hummer's method followed by reduction of antimony film by in‐situ electrodeposition. The experimental process could be concluded in three main steps: preparation of antimony film, reduction of analyte ions on the electrode surface and stripping step under the conditions of square wave anodic stripping voltammetry (SWASV). A simple and rapid approach was developed for the determination of heavy metals simultaneously based on a sequential injection (SI), an automated flow‐based system, coupled with voltammetric method using antimony‐graphene oxide modified screen‐printed carbon electrode (SbF‐GO‐SPCE). The effects of main parameters involved with graphene oxide, antimony and measurement parameters were also investigated. Using SI‐SWASV under the optimal conditions, the proposed electrode platform has exhibited linear range from 0.1 to 1.5 M. Calculated limits of detection were 0.054, 0.026, 0.060, and 0.066 μM for Cd(II), Pb(II), Cu(II) and Hg(II), respectively. In addition, the optimized method has been successfully applied to determine heavy metals in real water samples with acceptable accuracy of 94.29 – 113.42 % recovery.     

Development of a new stir bar sorptive extraction coating and its application for the determination of six pesticides in sugarcane juice

In this article, a novel polydimethylsiloxane/activated carbon (PDMS‐ACB) material is proposed as a new polymeric phase for stir bar sorptive extraction (SBSE). The PDMS‐ACB stir bar, assembled using a simple Teflon^®/glass capillary mold, demonstrated remarkable stability and resistance to organic solvents for more than 150 extractions. The SBSE bar has a diameter of 2.36 mm and a length of 2.2 cm and is prepared to contain 92 μL of polymer coating. This new PDMS‐ACB bar was evaluated for its ability to determine the quantity of pesticides in sugarcane juice samples by performing liquid desorption (LD) in 200 μL of ethyl acetate and analyzing the solvent through gas chromatography coupled with mass spectrometry (GC‐MS). A fractional factorial design was used to evaluate the main parameters involved in the extraction procedure. Then, a central composite design with a star configuration was used to optimize the significant extraction parameters. The method used demonstrated a limit of quantification (LOQ) of 0.5–40 μg/L, depending on the analyte detected; the amount of recovery varied from 0.18 to 49.50%, and the intraday precision ranged from 0.072 to 8.40%. The method was used in the analysis of real sugarcane juice samples commercially available in local markets.