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.     

Anodic Stripping Voltammetry Determination of Pb(II) and Cd(II) at a Bismuth/Poly(aniline) Film Electrode

Abstract

A novel voltammetric method—anodic—using a bismuth/poly(aniline) film electrode has been developed for simultaneous measurement of Pb(II) and Cd(II) at low µg L^?1 concentration levels by stripping voltammetry. The results confirmed that the bismuth/poly(aniline) film electrode offered high‐quality stripping performance compared with the bismuth film electrode. Well‐defined sharp stripping peaks were observed for Pb(II) and Cd(II), along with an extremely low baseline. The detection limits of Pb(II) and Cd(II) are 1.03 µg L^?1 and 1.48 µg L^?1, respectively. The bismuth/poly (aniline) electrode has been applied to the determination of Pb(II) in tap water samples with satisfactory results.     

Simultaneous determination of cadmium(II), lead(II) and copper(II) by using a screen-printed electrode modified with mercury nano-droplets

We are presenting a strategy for the fabrication of disposable screen-printed electrodes modified with mercury nano-droplets and capable of sensing heavy metal ions. They were prepared by coating electrodes with a mixture of multi-walled carbon nanotubes and chitosan, this followed by adsorption of mercury. The resulting sensor was characterized by cyclic voltammetry and impedance spectroscopy. Also the effects caused by adsorption of mercury were investigated. It is shown that square wave anodic stripping voltammetry enables simultaneous determination of cadmium(II), lead(II) and copper(II), for which detection limits of 12, 23 and 20 nM, respectively, are found. Relative standard deviations for ten determinations at 0.6 µM concentrations of these ions are in the range of 3.0 to 5.7%. The applicability was tested by analyzing river water and showed recoveries between 94.1 and 104.6%, thus demonstrating its utility for in-field monitoring of these heavy metal ions.     

A new potentiometric sensor based on a high-performance composite for nanomolar determination of mercury (II) in environmental samples

A new potentiometric sensor for the rapid determination of Hg²⁺ based on modified carbon paste electrode consisting of room temperature ionic liquid, 1-Butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF₆), multi-walled carbon nanotubes (MWCNTs), alumina nanoparticles and a synthetic macrocyclic diamide ‘7,10,13-triaza-1-thia-4,16-dioxa-6,14-dioxo-2,3;17,18-dinaphtho-cyclooctadecane’ as an efficient ionophore was constructed. Prepared composite is an ideal paste because it has low drift of potential, high selectivity and fast response time (10 s), which leads to a more stable potential signal. The morphology and properties of electrodes surface were characterised by scanning electron microscopy (SEM) and electrochemical impedance spectroscopy. A linear dynamic range of 2.01–2.01 × 10⁷ µg L^?1 with detection limit of 1.40 µg L^?1 Hg²⁺ was obtained at pH range of 2.5 to 4.5. The prepared modified electrode shows several advantages such as simple preparation method, high stability of the composite paste, high sensitivity, long-term life time (at least 13 weeks) and remarkable potentiometric reproducibility. The modified electrode was successfully applied for the accurate determination of trace amounts of Hg ²⁺ in environmental samples.     

Effect of Mercury(II) Traces on Catalytic Activity of Peanut and Horseradish Peroxidases

Abstract

Mercury(II) in the range of 0.1–1 µg L^?1 concentrations was found to be a much more efficient inhibitor of native peanut peroxidase (PNP) than of horseradish peroxidase (HRP) in the reaction of o‐dianisidine oxidation with hydrogen peroxide. The possible reason for the different degree of mercury(II) effects on the catalytic activity of both enzymes was studied. It was shown that the different number of glycans in PNP and HRP molecules (three and eight, respectively), or their absence in the molecule of wild‐type recombinant horseradish peroxidase refolded from E. coli inclusion bodies (recHRP), does not play a significant role in the effects caused by mercury(II). The efficient inhibition of PNP by mercury(II) in the absence of any other additives (for example, thiourea) originates from a greater mobility of the distal calcium ion in the enzyme molecule. A model scheme for the interaction of the studied plant peroxidases with mercury(II) was proposed. The PNP‐based enzymatic method for mercury(II) determination with c _min =0.04 µg L^?1 (0.2 nmol L^?1) was developed and the possibility of PNP application for analysis of different samples was demonstrated.     

Selenium-coated carbon electrode for anodic stripping voltammetric determination of copper(II)

We describe a new and promising type of selenium film electrode for anodic stripping voltammetry. This method is based on formation of copper selenide onto an in-situ formed selenium-film carbon electrode, this followed by Osteryoung square-wave anodic stripping voltammetry. Copper(II) is also in-situ electroplated in a test solution containing 0.01 mol L^-1 hydrochloric acid, 0.05 mol L^?1 potassium chloride and 500 µg L^?1 Se(IV) at a deposition potential of ?300 mV. The well-defined anodic peak current observed at about 200 mV is directly proportional to the Cu(II) concentration over the range from 1.0 to 100 µg L^?1 under the optimized conditions. The detection limit (three sigma level) is 0.2 µg L^?1 Cu(II) at 180 s deposition time. Relatively less interferences are shown from most of metal ions except for antimony(III). The method can be applied to analyses of river water and oyster tissue with good accuracy.     

Application of Ni(II)-imprinted cross-linked poly(methacrylic acid) synthesised through double-imprinting method for the on-line preconcentration of Ni(II) ions in aqueous media

The present paper describes the feasibility of on-line preconcentration of nickel ions from aqueous medium on Ni(II)-imprinted cross-linked poly(methacrylic acid) (IIP) synthesised through a double-imprinting method and their subsequent determination by FAAS. The proposed method consisted in loading the sample (20.0 mL, pH 7.25) through a mini-column packed with 50 mg of the IIP for 2 min. The elution step was performed with 1.0 mol L^?1 HNO₃ at a flow rate of 7.0 mL min^?1. The following parameters were obtained: quantification limit (QL) – 3.74 µg L^?1, preconcentration factor (PF) – 36, consumption index (CI) – 0.55 mL, concentration efficiency (CE) – 18 min^?1, and sample throughput – 25 h^?1. The precision of the procedure assessed in terms of repeatability for ten determinations was 5.6% and 2.5% for respective concentrations of 5.0 and 110.0 µg L^?1. Moreover, the analytical curve was obtained in the range of 5.0–180.0 µg L^?1 (r = 0.9973), and a 1.64-fold increase in the method sensitivity was observed when compared with the analytical curve constructed for the NIP (non-imprinted polymer), thus suggesting a synergistic effect of the Ni(II) ions and CTAB on the adsorption properties of the IIP. The practical application of the adsorbent was evaluated from an analysis of tap, mineral, lake and river water. Considering the results of addition and recovery experiments (90.2–100 %), the efficiency of this adsorbent can be ensured for the interference-free preconcentration of the Ni(II) ions.     

Dispersive Liquid–Liquid Microextraction of Silver Prior to Determination by Microsample Introduction-Flame Atomic Absorption Spectrometry

Abstract

A new simple and sensitive method has been proposed for rapid determination of trace levels of silver in environmental water samples, using dispersive liquid–liquid microextraction (DLLME) prior to its microsample introduction-flame atomic absorption spectrometry. Under the optimum conditions, the linear range was 0.1–7 µg L^?1 and limit of detection was 0.018 µg L^?1. The relative standard deviation for 0.50 and 5.00 µg L^?1 of silver in water sample was 4.0 and 1.7%, respectively. The relative recoveries of silver from tap, well, river, and seawater samples at spiking levels of 1.00 and 5.00 µg L^?1 were in the range of 86.4–98.6%.     

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.     

Carbamate Insecticide Sensing Based on Acetylcholinesterase/Prussian Blue-Multi-Walled Carbon Nanotubes/Screen-Printed Electrodes

Prussian blue (PB)-multi-walled carbon nanotubes (MWCNTs) modified screen-printed electrodes (SPEs) were used to immobilize enzyme acetylcholinesterase (AChE) for carbamate insecticide sensing. The synthesized hybrid PB-MWCNTs had high stability at pH values in the range of 5–10 and presented a porous and homogeneous microenvironment to entrap enzyme molecules. The generated hybrids not only acted as carriers of acetyl cholinesterase, but also promoted electron-transfer reactions because of the synergistic effects between MWCNTs and PB. Under the optimal conditions, the response of the sensor was proportional to acetylthiocholine (ATCh) concentrations ranging from 0.1 mM to 0.6 mM, with a sensitivity of 21.97 µA · mM^?1 · cm^?2. The sensors were further used to detect pesticides, and the inhibition rate of pirimicarb was proportional to the logarithm of its concentration ranging from 1.0 × 10^?6 to 1.0 g · L^?1, with a limit of detection (LOD) equal to 5.32 × 10^?8 g · L^?1. In order to evaluate the performance of the detection system, the sensors were applied to determine pirimicarb in water samples and exhibited high sensitivity and good stability. The detection system is fast, simple for analysis of pirimicarb in environmental samples, and could provide a semi-automated analytical system through further improvement in biosensor arrays.     

Gold nanoparticle modified screen-printed carbon arrays for the simultaneous electrochemical analysis of lead and copper in tap water

Disposable screen-printed carbon arrays modified with gold nanoparticles (AuNPs) are described. The AuNP-modified screen-printed carbon arrays, designated as AuNP-SPCE arrays, were characterized by cyclic voltammetry and electrochemical impedance spectroscopy. The AuNP-SPCE arrays display excellent electrocatalytic activity towards lead and copper. Two well-defined and fully resolved anodic stripping peaks, at 20 mV for Pb(II) and at 370 mV for Cu(II), both vs. Ag/AgCl, can be seen. Square wave anodic stripping voltammetry was used to simultaneously analyze Pb(II) and Cu(II) in their binary mixtures in tap water. The linear working range for Pb(II) extends from 10 μg.L^?1 to 100 μg.L^?1 with a sensitivity of 5.94 μA.μg^?1.L.cm^?2. The respective data for Cu(II) are a working range from 10 μg.L^?1 to 150 μg.L^?1 with a sensitivity of 3.52 μA.μg^?1.L.cm^?2. The limits of detection (based on 3× the baseline noise) are 2.1 ng.L^?1 and 1.4 ng.L^?1, respectively. In our perception, this array is particularly attractive because Pb(II) and Cu(II) can be determined at rather low working potentials which makes the method fairly selective in that it is not significantly interfered by other electroactive species that require higher reduction potentials.

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Graphical abstract Fabrication, characterization and electrochemical behavior of gold nanoparticles modified screen-printed carbon arrays towards lead and copper in tap water.

     

Solid phase extraction of Pd(II) on a newly synthesized chelating resin prior to determination by flame atomic absorption spectrometry

A new solid phase extraction method for the separation and preconcentration of Pd(II) was developed. As solid phase material, a new chelating polymer, poly [N-(4-bromophenyl)-2-methacrylamide-co-2-acrylamido-2-methyl-1-propanesulfonic acid - co-divinylbenzene] was synthesized. The parameters such as the effect of pH, eluent type, volume and concentration, flow rate of sample solution, sample volume and effect of interfering ions for the preconcentration of Pd(II) were investigated. The optimum pH was found to be 9. Eluent for quantitative elution was 10 mL of 1 mol L^?1 HCl. The preconcentration factor of the method was 75. At optimum conditions, the recovery for Pd(II) was found to be 101?±?4%. The limit of detection (3σ) was 1.1?µg L^?1. The method was applied to the determination of palladium in tap water and converter samples with satisfactory results.     

Mercury speciation by a high performance liquid chromatography—atomic fluorescence spectrometry hyphenated system with photo-induced chemical vapour generation reagent in the mobile phase

Speciation of mercury was accomplished by using a simple interface with photo-induced chemical vapour generation in a high performance liquid chromatography—atomic fluorescence spectrometry (HPLC-AFS) hyphenated system. Acetic acid and 2-mercaptoethanol in the mobile phase were used as photochemical reagent. The operating parameters were optimized to give limits of detection of 0.53 µg L^?1, 0.22 µg L^?1, 0.18 µg L^?1 and 0.25 µg L^?1 for inorganic mercury, methylmercury, ethylmercury and phenylmercury, respectively. The method was validated with the certified reference material DORM-2 and applied to the analysis of seafood samples. The HPLC-AFS hyphenated system is simple, environmentally friendly, and represents an attractive alternative to the conventional peroxothiosulfate-borohydride method.     

Polythiophene-coated Fe3O4 nanoparticles as a selective adsorbent for magnetic solid-phase extraction of silver(I), gold(III), copper(II) and palladium(II)

We have developed a fast method for sensitive extraction and determination of the metal ions silver(I), gold(III), copper(II) and palladium(II). Fe₃O₄ magnetic nanoparticles were modified with polythiophene and used for extraction the metal ions without a chelating agent. Following extraction, the ions were determined by flow injection inductively coupled plasma optical emission spectrometry. The influence of sample pH, type and volume of eluent, amount of adsorbent, sample volume and time of adsorption and desorption were optimized. Under the optimum conditions, the calibration plots are linear in the 0.75 to 100 μg L^?1 concentration range (R²?>?0.998), limits of detection in the range from 0.2 to 2.0 μg L^?1, and enhancement factors in the range from 70 to 129. Precisions, expressed as relative standard deviations, are lower than 4.2 %. The applicability of the method was demonstrated by the successful analysis of tap water, mineral water, and river water.

Square-Wave Anodic Stripping Voltammetry (SWASV) for the Determination of Ecotoxic Metals,Using a Bismuth-Film Electrode

This article reviews the use of square wave anodic stripping voltammetry for the simultaneous determination of ecotoxic metals (Pb, Cd, Cu, and Zn) on a bismuth-film (BiFE) electrode. The BiFE was prepared in situ on a glassy-carbon electrode (GCE) from the 0.1 mol L^?1 acetate buffer solution (pH 4.5) containing 200 µg L^?1 of bismuth (III). The addition of hydrogen peroxide to the electroanalytical cell proved beneficial for the interference-free determination of Cu (II) together with zinc, lead, and cadmium, using the BiFE. The experimental variables were investigated and optimized with the view to apply this type of voltammetric sensor to real samples containing traces of these metals. The performance characteristics, such as reproducibility, decision limit (CC_a), detection capability (CC_β), sensitivity, and accuracy indicated that the method holds promise for trace Cu²⁺, Pb²⁺, Cd²⁺, and Zn²⁺ levels by employment of Hg-free GCE with SWASV. CCa, and CCβ were calculated according to the Commission Decision of 12 August 2002 (2002/657/EC). Linearity was observed in the range 20–280 µg L^?1 for zinc, 10–100 µg L^?1 for lead, 10–80 µg L^?1 for copper, and 5–50 µg L^?1 for cadmium. Using the optimized conditions, the stripping performance of the BiFE was characterized by low limits of detection (LOD). Finally, the method was successfully applied in real as well as in certified reference water samples.     

Simultaneous Electrochemical Determination of Hydroquinone and Catechol at MWNTs and Cobalt(II) Tetrakisphenylporphyrin Modified Electrode

A multi-wall carbon nanotubes (MWNTs) and cobalt(II) tetrakisphenylporphyrin (Co(II)TPP) modified glassy carbon electrode (MWNTs/Co(II)TPP/GCE) has been prepared. It can be used for individual or simultaneous determination of hydroquinone (HQ) and catechol (CC). The anodic peaks of HQ and CC can be separated well. Owing to the unique properties of MWNTs and special synergistic effect of MWNTs and Co(II)TPP, the modified electrode exhibited a remarkable and stable current response for CC and HQ. The linear ranges for CC and HQ were 1.0–450.0 µmol L^?1 and 0.8–400.0 µmol L^?1 with detection limits of 0.8 µmol L^?1 and 0.5 µmol L^?1, respectively. Furthermore, Co(II)TPP, MWNTs, and Co(II)TPP/MWNTs composite were also used to construct modified electrodes and the electrochemical performances were studied.     

On-line preconcentration and determination of Au(III) in various environmental/industrial samples by flame atomic absorption spectrometry

A rapid and simple on-line method is described for the determination of Au(III) in various samples. The method is based on the sorption of gold(III) on Lewatit MonoPlus TP207 chelating resin including the iminodiacetate group, which is used as sorbent material and packed in a minicolumn. The chemical variables such as the pH of the sample solution, eluent type, interfering ions and concentrations of reagents, and instrumental variables such as sample loading volume, reagents flow rates, and tubing length, which affect the efficiency of the method were studied and optimised. Au(III) was sorbed on the chelating resin, from which it could be eluted with 3 mol L^?1 HCl, and then introduced directly to the nebuliser-burner system of FAAS. The limit of detection of the method was 0.2 µg L^?1 while the relative standard deviation was <4.0% for 20 µg L^?1 Au(III) concentration. The preconcentration factor was found to be 106 while the optimised sample volume was 15.3 mL. The accuracy of the method was verified by analysing the certified reference material. The developed method was applied successfully for the determination of gold in different samples with satisfactory results.     

Ultra trace level square wave anodic stripping voltammetric sensing of mercury(II) ions in environmental samples using a Schiff base-modified carbon paste electrode

ABSTRACT

In this approach, a new carbon paste electrode modified with N,N′-bis(5-bromo-2-hydroxybenzylidene)-2,2-dimethylpropane-1,3-diamine Schiff base ligand (L) was synthesised for selective and effective determination of Hg²⁺ ions in aqueous environmental samples using cyclic and square wave anodic stripping voltammetric methods. First, the selective detection of mercury ion was confirmed by evaluating the stability constants of metal complexes formed between the Schiff base ligand (L) and some desired cations by conductometric measurements. Afterwards, by preparing an effective carbon paste electrode modified with L, the experimental and instrumental parameters affecting the performance of modified electrode were investigated. Square wave anodic stripping voltammograms were obtained after applying an accumulation potential ?0.5 V and accumulation time 150 s in Britton–Robinson buffer solution at pH 2.0. The optimal square wave parameters found are pulse amplitude 75 mV, frequency 50 Hz and step potential 6 mV. The procedure exhibited linear range from 0.4 to 120 μg L^?1 Hg²⁺ with a limit of detection of 0.042 μg L^?1. The proposed electrode was proved to be highly selective in the presence of various cations and anions and was successfully used for determination of mercury in tobacco and several water samples.     

Screen-Printed Electrodes Modified by Bismuth Film for the Determination of Released Lead in Moroccan Ceramics

Abstract

Screen-printing technology is a particularly attractive technique for the mass production of cheap and disposable sensors, and the use of screen-printed electrodes (SPEs) in conjunction with portable, electrochemical instrumention greatly facilitates the feasibility of on-site testing. In this work, a simple, electrochemical method using screen-printed probes has been applied to test for the presence of released lead (Pb) in the glazes of different ceramic tajines collected randomly from a local market square in Morocco. Square-wave anodic voltammetry (SWAV) was employed with SPEs that had been modified with a bismuth film and 5 µl of 0.5% nafion (SPEBi-Na). This probe displayed excellent linear behavior over the examined concentration range, from 5 to 80 µg/L Pb²⁺ in 100 mM acetate buffer, pH 5, with a detection limit of 4 ppb for lead and (r² = 0.9972). The good reproducibility obtained with this system led us to apply it to determine lead in this typical Moroccan cookware under conditions relevant to its use. The results showed that when tajines containing 3% acetic acid were heated for 30 min, the amounts of leached lead ranged from 16.8 to 26.4 ppm. When the tajines contains lemon instead of 3% acetic acid and was heated for 30 min, then amounts of lead released exceeded 37 ppm. These values are greater than the allowed maximum concentrations in the United States and Canada.     

Electrochemical Characterization of and Stripping Voltammetry at Screen Printed Electrodes Modified with Different Brands of Multiwall Carbon Nanotubes and Bismuth Films

A screen-printed electrode sensor has been fabricated by modifying the carbon ink surface with different brands of multiwall carbon nanotubes (MWCNTs) and bismuth film (BiF) for the determination of traces of lead, cadmium and zinc ions by square wave anodic stripping voltammetry. The MWCNTs, from three different sources, were functionalized and dispersed in Nafion (MWCNT-Nafion) solution and placed on screen printed electrodes (MWCNT-Nafion/SPE); bismuth films were then prepared by ex-situ plating of bismuth onto the MWCNT-Nafion/SPE electrodes. The electrochemical characteristics of BiF/MWCNT-Nafion/SPE/ were examined by electrochemical impedance spectroscopy and showed differences; the charge transfer resistance tends to decrease with negative applied potentials. After optimizing the experimental conditions, the square-wave peak current signal is linear in the nmol L^?1 range. The lowest limit of detection found for the separate determination of lead, cadmium and zinc were 0.7 nmol L^?1, 1.5 nmol L^?1, and 11.1 nmol L^?1, respectively, with a 120 s deposition time.