Electrode Modified with Langmuir–Blodgett (LB) Film of Calixarenes for Preconcentration and Stripping Analysis of Hg(II)

A new type of current sensor, Langmuir–Blodgett (LB) film of calixarene on the surface of glassy carbon electrode (GCE) was prepared for determination of mercury by anodic stripping voltammetry (ASV). An anodic stripping peak was obtained at 0.15 V (vs. SCE) by scanning the potential from ?0.6 to +0.6 V. Compared with a bare GCE, the LB film coated electrode greatly improves the sensitivity of measuring mercury ion. The fabricated electrode in a 0.1 M H₂SO₄+0.01 M HCl solution shows a linear voltammetric response in the range of 0.07–40 μg L^?1 and detection limit of 0.04 μg L^?1 (ca. 2×10^?10 M). The high sensitivity, selectivity, and stability of this LB film modified electrode demonstrates its practical application for a simple, rapid and economical determination of Hg²⁺ in a water sample.     

A glassy carbon electrode modified with antimony and poly(p-aminobenzene sulfonic acid) for sensing lead(II) by square wave anodic stripping voltammetry

We have developed a sensor for the square wave anodic stripping voltammetric determination of Pb(II). A glassy carbon electrode was modified with a thin film of an antimony/poly(p-aminobenzene sulfonic acid) composite in air-saturated aqueous solution of pH 2.0. Compared to a conventional antimony film electrode, the new one yields a larger stripping signal for Pb(II). The conditions of polymerization, the concentration of Sb(III), the pH value of the sample solution, the deposition potential and time, frequency, potential amplitude, and step increment potential were optimized. Under the optimum conditions, a linear response was observed for Pb(II) in the range of 0.5 to 150.0 μg?L^?1. The detection limit for Pb(II) is 0.1 μg?L^?1.

Voltammetric Determination of Phenoxybenzyl‐Type Insecticides at Chemically Modified Conducting Polymer‐Carbon Nanotubes Coated Electrodes

The electrochemical reduction of three common insecticides such as cypermethrin (CYP), deltamethrin (DEL) and fenvalerate (FEN) was investigated at glassy carbon electrode (GCE), multiwalled carbon nanotubes modified GCE (MWCNT‐GCE), polyaniline (herein called as modifier M₁) and polypyrrole (herein called as modifier M₂) deposited MWCNT/GCE using cyclic voltammetry. Influences of pH, scan rate, and concentration were studied. The surface morphology of the modified film was characterized by scanning electron microscopy (SEM) and X‐ray diffraction analysis (XRD). A systematic study of the experimental parameters that affect differential pulse stripping voltammetry (DPSV) was carried out and the optimized experimental conditions were arrived at. The calibration plots were linear over the insecticide's concentration range 0.1–100 mg L^?1 and 0.05–100 mg L^?1 for all the three insecticides at MWCNT‐GCE and MWCNT(M₁)‐GCE respectively. The MWCNT(M₂)‐GCE performed well among the three electrode systems and the determination range obtained was 0.01–100 mg L^?1 for CYP, DEL and FEN. The limit of detection (LOD) was 0.35 μg L^?1, 0.9 μg L^?1 and 0.1 μg L^?1 for CYP, DEL and FEN respectively on MWCNT(M₂)‐GCE modified system. Suitability of this method for the trace determination of insecticide in spiked soil sample was also determined.     

Electroanalytical Determination of Cadmium(II) and Lead(II) Using an Antimony Nanoparticle Modified Boron‐Doped Diamond Electrode

We report the simultaneous electroanalytical determination of Pb²⁺ and Cd²⁺ by linear sweep anodic stripping voltammetry (LSASV) using an antimony nanoparticle modified boron doped diamond (Sb‐BDD) electrode. Sb deposition was performed in situ with the analytes, from a solution of 1 mg L^?1 SbCl₃ in 0.1 M HCl (pH 1). Pb²⁺ inhibited the detection of Cd²⁺ during simultaneous additions at the bare BDD electrode, whereas in the presence of antimony, both peaks were readily discernable and quantifiable over the linear range 50–500 μg L^?1.     

Differential Pulse Anodic Stripping Voltammetric Determination of Bismuth(III) with 1‐(2‐Pyridylazo)‐2‐naphthol and Ionic Liquid Modified Carbon Paste Electrode

In this paper 1‐(2‐pyridylazo)‐2‐naphthol (PAN) and ionic liquid 1‐ethyl‐3‐methylimidazolium tetrafluoroborate (EMIMBF₄) were mixed with graphite powder to get a modified carbon paste electrode (PAN‐IL‐CPE), which was further used for the sensitive determination of bismuth(III). By the co‐contribution of the formation of PAN‐Bi complex and the accumulation effect of IL, more bismuth(III) was electrodeposited on the surface of the PAN‐IL‐CPE. Then the reduced Bi was oxidized and detected by differential pulse anodic stripping voltammetry (DPASV) with the oxidation peak appeared at 0.17 V (vs. SCE). Under the optimal conditions the oxidation peak current was proportional to the bismuth(III) concentration in the range from 0.04 to 7.5 μmol L^?1 with the detection limit as 3.9 nmol L^?1. The proposed method was successfully applied to the stomach medicine sample detection with good recovery.     

Amplified Electrochemical Response of Phenol by Oxygenation of Tyrosinase Coupling with Electrochemical‐chemical‐chemical Redox Cycle

In this work, an novel electrochemical‐chemical‐chemical (ECC) redox cycle was designed in an enzyme‐based sensor for acquiring additional signal amplification. The tyrosinase (Tyr) was entrapped in a sulfonated polyaniline?chitosan (SPAN?CS) composite which was used as a redox capacitor on a glass carbon electrode. Firstly, the substrate, phenol was catalyzed to catechol and further catalyzed to o‐benzoquinone by Tyr. Next, in the presence of Ru(NH₃)₆Cl₂, the reduced state of SPAN(SPAN_red) was reacted with o‐benzoquinone to form it's oxidized state (SPAN_ox) and catechol, then SPAN_ox was reduced back to SPAN_red by Ru(II) in the solution. Finally, the amplified anodic current of catechol was obtained on electrode through above ECC redox cycle system. In addition, the ECC redox cycling led to a high signal‐to‐background ratio. The voltammetric response showed excellent analytical performance to phenol over two linear range of 3.5 to 200.0 nmol L^?1 and 200.0 to 2000.0 nmol L^?1 with a high sensitivity of 2204 μA mM^?1. The detection limit was obtained to be 0.8 nmol L^?1 (S/N=3). Furthermore, the proposed approach exhibited good repeatability, stability and specificity, and could offer practicality in the detection of phenol in tap water.     

Square Wave‐Anodic Stripping Voltammetric Determination of Copper at a Bismuth Film/Glassy Carbon Electrode Using 3‐[(2‐Mercapto‐Vinyl)‐Hydrazono]‐ 1,3‐Dihydro‐Indol‐2‐One

This study reports a highly sensitive electrochemical sensor based on Bi film modified glassy carbon electrode (BiF/GCE) for total determination and speciation trace concentrations of copper(II) ions in environmental water samples. Square wave‐adsorptive anodic stripping voltammetric (SW‐ASV) experiment was performed for monitoring selective accumulation of copper(II) with reagent 3‐[(2‐mercapto‐vinyl)‐hydrazono]‐1,3‐dihydro‐indol‐2‐one (MHDI) at pH 9–10. The mechanism of the electrode reaction of Cu²⁺‐MHDI complex was safely assigned. The sensor exhibited a wide linear range (3.22×10⁻⁹–2.0×10⁻⁷ mol L⁻¹) with lower limits of detection (LOD) and quantitation (LOQ) of 9.6×1⁻¹⁰ and 3.22×10⁻⁹ mol L⁻¹, respectively (R²=0.9993). The proposed sensor exhibited interference from active metal ions e. g. Cd, Hg. The performance of the proposed method was compared successfully with most of the reported methods and comparable efficiencies were obtained. The analytical utility of the proposed SW‐ASV method has been successfully validated for trace analysis of copper(II) in environmental water samples. The method offers a precise, accurate approach with good reproducibility, robustness, ruggedness, and cost effectiveness.     

Tellurium Film Electrodes Deposited on Carbon and Mesoporous Carbon Screen‐printed Substrates for Anodic Stripping Voltammetric Determination of Copper

The performance of screen‐printed electrodes modified in situ with tellurium film for the anodic stripping voltammetric (ASV) determination of Cu(II) is reported. It was found that two types of screen‐printed substrates, namely carbon and mesoporous carbon, were optimal for this application. The selected in situ tellurium film modified electrodes were applied for the square wave ASV determination of copper at μg L⁻¹ concentration levels. Well‐defined and reproducible Cu oxidation stripping peaks were produced at a potential more negative than the anodic dissolution of tellurium. The highest sensitivity of Cu determination was achieved in 0.05 M HCl containing 50 μg L⁻¹ Te(IV) after 300 s of accumulation at −0.5 V. Using the optimized procedure, a linear range from 2 to 35 μg L⁻¹ of Cu(II) was obtained with a detection limit of 0.5 μg L⁻¹ Cu(II) (S/N=3) for 300 s of deposition time. Both sensors, carbon TeF‐SPE and mesoporous carbon TeF‐SPE, were successfully applied for the quantification of Cu in a certified reference surface water sample.     

A Self‐assembled L‐Cysteine and Electrodeposited Gold Nanoparticles‐reduced Graphene Oxide Modified Electrode for Adsorptive Stripping Determination of Copper

Glassy carbon electrode (GCE) modified with L‐cysteine and gold nanoparticles‐reduced graphene oxide (AuNPs‐RGO) composite was fabricated as a novel electrochemical sensor for the determination of Cu²⁺. The AuNPs‐RGO composite was formed on GCE surface by electrodeposition. The L‐cysteine was decorated on AuNPs by self‐assembly. Physicochemical and electrochemical properties of L‐cysteine/AuNPs‐RGO/GCE were characterized by scanning electron microscopy, atomic force microscopy, energy dispersive spectroscopy, Raman spectroscopy, X‐ray diffraction, cyclic voltammetry and adsorptive stripping voltammetry. The results validated that the prepared electrode had many attractive features, such as large electroactive area, good electrical conductivity and high sensitivity. Experimental conditions, including electrodeposition cycle, self‐assembly time, electrolyte pH and preconcentration time were studied and optimized. Stripping signals obtained from L‐cysteine/AuNPs‐RGO/GCE exhibited good linear relationship with Cu²⁺ concentrations in the range from 2 to 60 μg L⁻¹, with a detection limit of 0.037 μg L⁻¹. Finally, the prepared electrode was applied for the determination of Cu²⁺ in soil samples, and the results were in agreement with those obtained by inductively coupled plasma mass spectrometry.     

Selective Determination of Copper (II) Based on Aluminum Silicon Carbide Nanoparticles Modified Glassy Carbon Electrode by Square Wave Stripping Voltammetry

The morphology and structure of as‐prepared aluminum silicon carbide (Al₄SiC₄) were characterized using X‐ray diffraction (XRD) patterns, scanning electron microscope (SEM), transmission electron microscopy (TEM) and UV‐vis spectra. The Al₄SiC₄ nanoparticles modified glassy carbon electrode (GCE) was further investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Based on this, this kind of new electrode was used for the detection of trace Cu²⁺ by square wave anodic stripping voltammetry (SWASV) for the first time. The electrochemical parameters influencing on deposition and stripping of metal ions, such as supporting electrolytes, pH value, deposition potential and deposition time, were also optimized. The results showed that the Al₄SiC₄ modified GCE exhibited excellent stripping response of Cu²⁺ and the stripping peaks response increased linearly with increasing concentration of Cu²⁺ in the ranges of 400 to 2200 nM. Under the optimized conditions the favorable sensitivity of the Al₄SiC₄ modified GCE toward trace Cu²⁺ was 1.49 μA μM⁻¹ and the limit of detection (S/N=3) was estimated to be 2.76 nM. More importantly, Al₄SiC₄ modified GCE had an excellent stability and negligible interference from other coexisting metal ions in the electrochemical determination of Cu²⁺.     

Mercury‐modified Lignosulfonate‐stabilized Gold Nanoparticles as an Alternative Material for Anodic Stripping Voltammetry of Thallium

Lignosulfonate‐stabilized gold nanoparticles (AuNPs‐LS) were synthesized and subsequently used as a complexing agent for mercury ions. The obtained AuNPs‐LS/Hg²⁺ complex was characterized by means of various physicochemical techniques such as UV‐vis spectroscopy, transmission electron microscopy and cyclic voltammetry. Furthermore, the resulting complex was evaluated as an electrode modifier for the development of amperometric sensors. Upon sufficient negative potential, the bound mercury ions are reduced to form an amalgam with AuNPs‐LS. Thus, the performance of glassy carbon electrode (GCE) modified by AuNPs‐LS/Hg film was investigated as an electrochemical sensor in the determination of Tl⁺ ions in a 0.05 M EDTA at pH 4.5. The presence of the mercury containing film improves the analyte accumulation due to its ability to form a fused amalgam with thallium. The presented data indicate that the GCE/AuNPs‐LS/Hg modified electrode shows better performance toward Tl⁺ determination in comparison to bare GCE. The stripping anodic peak current of thallium was linear over its concentration range from 1.7⋅10⁻⁷ to 5.0⋅10⁻⁶ M. The detection limit (3σ) was estimated to be 1.4⋅10⁻⁷ M. The proposed method was successfully applied for the determination of thallium ions in real samples of soil derived from the area of the copper smelter near Głogów (Poland).     

Simultaneous Electrochemical Detection of Co(II) and Cu(II) by 1‐Diazo‐2‐Naphthol‐4‐Sulfonic Acid/MWCNTs Modified Electrode

This work describes a simple preparation of 1‐diazo‐2‐naphthol‐4‐sulfonic acid (1,2,4‐acid) and multiwalled carbon nanotubes (MWCNTs) modified glassy carbon electrode (GCE) for the simultaneous detection of Co(II) and Cu(II). MWCNTs, with their good conductivity and large surface area, were drop‐casted onto the surface of the GCE prior to the electrodeposition of 1,2,4‐acid, a metal chelating agent. Co(II) and Cu(II) were simultaneously measured by differential pulse anodic stripping voltammetry (DPASV) in a batch system. Under optimum conditions, the linear range of Co(II) was between 0.10 and 2.5 μg mL⁻¹ with an LOD of 80 ng mL⁻¹. Two linear ranges were obtained for Cu(II), 0.0050 to 0.030 μg mL⁻¹ and 0.040 to 0.25 μg mL⁻¹,with an LOD of 2.4 ng mL⁻¹. The method offered a high operational stability for up to 52 measurements (RSD=3.4 % for Co(II) and 2.6 % for Cu(II)) and good reproducibility (RSD=1.2 % for Co(II) and 1.7 % for Cu(II)). In the simultaneous detection of Co(II) and Cu(II), there was no effect from common interferences found in wastewater. The method was successfully applied in real water samples with good recoveries (88.2±0.8 to 102.0±0.8 % for Co(II) and 96.5±0.4 to 103.8±0.9 % for Cu(II)) and the results were in good agreement with those obtained from inductively coupled plasma optical emission spectrometry (ICP‐OES) (P >0.05).     

Electrocatalytic Oxidation of Acyclovir on Poly(p‐Aminobenzene Sulfonic Acid) Film Modified Glassy Carbon Electrode

Acyclovir is an antiviral effective drug active compound. A glassy carbon electrode (GCE) was modified with an electropolymerized film of p‐aminobenzene sulfonic acid (p‐ABSA) in phosphate buffer solution (PBS). The polymer film‐modified electrode was used to electrochemically detect acyclovir. Polymer film showed excellent electrocatalytic activity for the oxidation of acyclovir. The anodic peak potential value of the acyclovir at the poly(p‐ABSA) modified glassy carbon electrode was 950 mV obtained by DPV. A linear calibration curve for DPV analysis was constructed in the acyclovir concentration range 2×10^?7–9×10^?6 mol L^?1. Limit of detection (LOD) and limit of quantification (LOQ) were obtained as 5.57×10^?8 and 1.85×10^?7 mol L^?1 respectively. The proposed method exhibits good recovery and reproducibility.     

Development of a Sensor Based on Poly(1,2-diaminoanthraquinone) for Individual and Simultaneous Determination of Mercury (II) and Bismuth (III)

Contamination of natural water by mercury (Hg²⁺) and bismuth (Bi³⁺) metal ions have been extensively studied due to their toxic effects. A validated square-wave anodic stripping voltammetry (SW-ASV) method for determining Bi³⁺ and Hg²⁺ ions individually and simultaneously is described. A new electrochemical sensor was constructed using a gold (Au) electrode that has been modified with poly(1,2-diaminoanthraquinone) (p-1,2-DAAQ). Scanning electron microscopy, cyclic voltammetry, and electrochemical impedance spectroscopy were used to characterize the p-1,2-DAAQ/Au modified electrode. Factors such as the polymer film thickness, electrolyte, square wave parameters and preconcentration conditions were optimized to improve the performance of the modified Au electrode. Good linear responses were achieved in the concentration ranges of 1–200 μg L⁻¹ and 1–50 μg L⁻¹ forBi³⁺ and Hg²⁺, respectively, and the limits of detection were 0.27 μg L⁻¹ (Bi³⁺) and 0.29 μg L⁻¹ (Hg²⁺). The interference study results illustrated the high selectivity of the modified electrode for detection of Bi³⁺ and Hg²⁺. The proposed SW-ASV method was successfully applied for Bi³⁺ and Hg²⁺analyses in different real water samples.     

Gold Nanoparticles-electrochemically Reduced Graphene Oxide/Poly(indole-5-carboxylic acid) Nanocomposite for Electrochemical Non-enzymatic Sensing of Hydrogen Peroxide

Herein, co-electrodeposition of AuNPs and ERGO onto GCE was conducted to prepare the modified electrode, GCE/AuNPs-ERGO. The poly(indole-5-carboxylic acid) (P(In-5-COOH) was then coated onto the GCE/AuNPs-ERGO with the help of electropolymerization. FT-IR, FE-SEM and EDX, and XRD techniques were employed to characterize the prepared nanocomposite. The nanocomposite modified electrode (GCE/AuNPs-ERGO/P(In-5-COOH)) was examined for the electrochemical reduction of H₂O₂ using chronoamperometry. A high reduction current for H₂O₂ was observed due to the synergistic effect between AuNPs-ERGO and P(In-5-COOH). The proposed sensor demonstrated a wide linear range of 0.025–750 μmol L⁻¹, with a LOD of 0.008 μmol L⁻¹ at −0.4 V. Furthermore, the developed sensor was applied for the detection of H₂O₂ in fetal bovine serum and urine 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.     

Determination of Some Heavy Metal Ions with a Carbon Paste Electrode Modified by Poly(glycidylmethacrylate‐methylmethacrylate‐divinylbenzene) Microspheres Functionalized by 2‐Aminothiazole

A carbon paste electrode modified with 2‐aminothiazole functionalized poly(glycidylmethacrylate‐methylmethacrylate‐divinylbenzene) microspheres was used for trace determination of mercury, copper and lead ions. After the open‐circuit accumulation of the heavy metal ions onto the electrode, the sensitive anodic stripping peaks were obtained by square wave anodic stripping voltammetry (SWASV)). Many parameters such as the composition of the paste, pH, preconcentration time, effective potential scan rate and stirring rate influence the response of the measurement. The procedures were optimized for most sensitive and reliable determinations of the desired species. For a 10‐min preconcentration time in synthetic solutions at optimum instrumental and experimental conditions, the detection limit (LOD) was 12.3, 2.8 and 4.5 μg L^?1 for mercury, copper and lead, respectively. The limits of detection may be enhanced by increasing the preconcentration time. For example, LOD of mercury and copper was 4.9 and 1.0 μg L^?1 for fifteen minutes preconcentration time. The sensitivity may also considered to be increased by using a more suitable electrode composition targeting the more conductive electrode with lesser amount of modified polymer for sub‐μg L^?1 levels of heavy metal ions. The optimized method was successfully applied to the determination of copper in tap water and waste water samples by means of standard addition procedure. The copper content found was comparable with the certified concentration of the waste water sample. The calibration plots for mercury and lead spiked real samples were also drawn.     

Stripping Voltammetric Determination of Methyl Parathion at Activated Carbon Nanopowder Modified Electrode

An activated carbon nanopowder modified glassy carbon electrode (AC-GCE) was constructed for the sensitive determination of methyl parathion by adsorptive differential pulse anodic stripping voltammetry. The simple and rapid modification procedure included only drop-coating the electrode surface with a laponite stabilized activated carbon nanopowder suspension and drying. The modifier high adsorption ability, combined with its large electroactive surface area allowed a 30-fold signal increase to be achieved, compared to bare GCE. Under optimized experimental conditions (activated carbon to laponite ratio, pH and accumulation time), the AC-GCE exhibited a linear response to methyl parathion in two concentration ranges: from 0.01 μmol L⁻¹ to 1 μmol L⁻¹ and from 1 μmol L⁻¹ to 6 μmol L⁻¹. The LOD of 2.5 nmol L⁻¹ (S/N=3) achieved fitted with regulatory norms. It was demonstrated that the as-prepared AC-GCE is suitable for routine real samples analysis.     

Development of an Electrochemical Sensor to Detect Dopamine and Ascorbic Acid Based on Neodymium (III) Oxide and Chitosan

Neodymium (III) oxide (Nd_Ox) was dispersed in chitosan dissolution and deposited on a glassy carbon electrode (chitosan‐Nd_Ox/GCE). The surface properties of the chitosan‐Nd_Ox/GCE were evaluated with FeCN₆⁻³ solution using cyclic voltammetry and electrochemical impedance spectroscopy. The modified electrode was used in the determination of individual dopamine (DP) and ascorbic acid (AA) with square wave adsorptive voltammetry. Under optimal parameters (pH 4.0; accumulation time; t_ACC 60s and accumulation potential; E_ACC 0.10 V) for DP and (pH 3,0; t_ACC 60s and; E_ACC −0.20 V) for AA, anodic peak currents were proportional to the concentration of DP and AA between 0.90 and 17.0 μmolL⁻¹, with detection limit of 0.079 μmolL⁻¹ for DP and 0.12 μmolL⁻¹ for AA. The sensor was used in the determination of DP and AA in human urine samples and vitamin C tablets with consistent results. The new sensor is easy to develop. In addition, the sensitivity in particular for AA was improved compared with previous work.     

Selective Determination of Total Capsaicinoids in Plant Material Using Poly(Gallic Acid)‐modified Electrode

Novel voltammetric approach for the selective determination of total capsaicinoids has been developed using glassy carbon electrode modified with multi‐walled carbon nanotubes and poly(gallic acid) (PGA/MWNT/GCE). The modified electrode provides significant improvements in the capsaicinoids voltammetric characteristics in comparison to GCE and MWNT/GCE. The electrooxidation of capsaicinoids is irreversible adsorption‐controlled process with the anodic transfer coefficient of 0.49–0.53 and heterogeneous electron transfer rate constant of 1300–2400 s^?1. The analytical ranges of 0.010–1.0 and 1.0–50 μM for capsaicin, 0.025–0.75 and 0.75–75 μM for dihydrocapsaicin and 0.025–5.0 and 5.0–75 μM for nonivamide with the detection limits of 2.9, 5.9 and 6.1 nM, respectively, have been obtained using differential pulse voltammetry (DPV). The selectivity of the capsaicinoids quantification in the presence of ascorbic acid, α‐tocopherol and carotenoids is shown. The method has been tested on the samples of red hot pepper spices and Capsicum annuum L. tinctures. The results correspond to the chromatographic data.