Lead Determination by Anodic Stripping Voltammetry Using a p‐Phenylenediamine Modified Carbon Paste Electrode

Carbon paste electrodes were modified by mixing appropriate amounts of the monomers o‐phenylendiamine, p‐phenylendiamine and m‐phenylendiamine (o‐PD, p‐PD and m‐PD) into a graphite powder‐paraffin oil matrix. The electropolymerization of the incorporated phenylendiamine was then carried out in a carbon paste electrode in acidic medium by cyclic voltammetry between ?0.30 V and +0.90 or under constant potential. The modified carbon paste electrodes (MCPEs) obtained by this electropolymerization method were found to be useful for trace determination of Pb²⁺ in aqueous solutions. Lead(II) was first preconcentrated on the modified electrodes by complexation with the modifier, and the electrode was then transferred to an electrochemical cell. The best results in terms of sensitivity and detection limit were obtained with poly p‐phenylenediamine (poly (p‐PD)). For a 10‐min preconcentration time, the calibration plot was linear from 5×10^?8 mol L^?1 to 10^?5 mol L^?1, with r²=0.999 and relative standard deviation equal to 5%. However, the lowest lead concentration that could be detected was 10^?9 mol L^?1. Interference from metal ions like Cd(II), Hg(II), Zn(II), Fe(II) and Cu(II) was also studied.     

Complexing Polymer Films in The Preparation of Modified Electrodes for Detection of Metal Ions

Summary: The complexing properties of poly (3-(pyrrol-1-yl)propylmalonic acid) (poly1) and poly(N,N′-ethylenebis[N-[(3-(pyrrole-1-yl)propyl) carbamoyl) methyl]-glycine (poly2) coated electrodes (C|poly1 and C|poly2) towards Cu(II), Pb(II), Hg(II) and Cd(II) cations using the open circuit chemical preconcentration-anodic stripping technique were studied. Sorption process of metal cations onto complexing surfaces was readily investigated through the combination of a chemical pre-concentration-anodic stripping technique with a Langmuir isotherm model. The modified electrodes were used for the voltammetric determination of Cu(II), Pb(II), Hg(II) and Cd(II) ions, giving low detection limits for Cu(II) (5 × 10⁻⁹ mol L⁻¹) and Pb(II) (5 × 10⁻¹⁰ mol L⁻¹). The ability of the modified electrodes to analyze Cu(II) ions in natural sample has been demonstrated by the analysis of a tap water sample. The results of the preconcentration process under competitive conditions clearly shows that the selectivity of complexing molecular electrode materials can be subtly tuned upon playing on the accumulation time, polymer thickness and/or memory effect of the binding polymers, opening up new avenues towards evolutive and efficient smart sensing materials.     

Label‐Free Photoelectrochemical Detection of Double‐Stranded HIV DNA by Means of a Metallointercalator‐Functionalized Electrogenerated Polymer

The design of photoactive functionalized electrodes for the sensitive transduction of double‐stranded DNA hybridization is reported. Multifunctional complex [Ru(bpy‐pyrrole)₂(dppn)]²⁺ (bpy‐pyrrole=4‐methyl‐4′‐butylpyrrole‐2,2′‐bipyridine, dppn=benzo[i]dipyrido[3,2‐a:2′,3′‐c]phenazine) exhibiting photosensitive, DNA‐intercalating, and electropolymerizable properties was synthesized and characterized. The pyrrole groups undergo oxidative electropolymerization on planar electrodes forming a metallopolymer layer on the electrode. Thanks to the photoelectrochemical and intercalating properties of the immobilized Ru^II complex, the binding of a double‐stranded HIV DNA target was photoelectrochemically detected on planar electrodes. Photocurrent generation through visible irradiation was correlated to the interaction between double‐stranded DNA and the metallointercalator polymer. These interactions were well fitted by using a Langmuir isotherm, which allowed a dissociation constant of 2×10⁶ L mol^?1 to be estimated. The low detection limit of 1 fmol L^?1 and sensitivity of 0.01 units per decade demonstrate excellent suitability of these modified electrodes for detection of duplex DNA.     

Potentiometric Ag+ Sensors Based on Conducting Polymers: A Comparison between Poly(3,4‐ethylenedioxythiophene) and Polypyrrole Doped with Sulfonated Calixarenes

Potentiometric Ag⁺ sensors were prepared by galvanostatic electropolymerization of 3,4‐ethylenedioxythiophene (EDOT) and pyrrole (Py) on glassy carbon electrodes by using sulfonated calixarenes as doping ions. Poly(3,4‐ethylenedioxythiophene) (PEDOT) and polypyrrole (PPy) doped with p‐sulfonic calix[4]arene (C4S), p‐sulfonic calix[6]arene (C6S) and p‐sulfonic calix[8]arene (C8S) were compared. PEDOT and PPy doped with poly(styrene sulfonate) (PSS) were also included for comparison. The analytical performance of the conducting polymer‐based Ag⁺ sensors was studied by potentiometric measurements. All conducting polymer and dopant combinations showed sensitivity and selectivity to Ag⁺ compared to several alkali, alkaline‐earth, and transition‐metal cations. The type of the conducting polymer used for the fabrication of the electrodes was found to have a more significant effect on the selectivity of the electrodes to Ag⁺ than the ring size of the sulfonated calixarenes used as dopants. Selected conducting polymer‐based sensors were studied by cyclic voltammetry (CV) and energy dispersive analysis of X‐rays (EDAX) measurements. Results from the EDAX measurements show that both PEDOT‐ and PPy‐based membranes accumulate silver.     

基于T-T碱基错配的荧光传感器特异性检测汞离子

在本文中,我们研制了一种基于T-T碱基错配特异性键合汞离子的荧光传感器用于汞离子的检测。该传感器由两条分别标记了荧光基团（F）和淬灭基团（Q）的DNA探针组成,并且含有两对用于结合汞离子的T-T错配碱基。当汞离子存在时,两条探针之间形成T-Hg2+-T结构,作用力增强,从而拉近了荧光基团与淬灭基团之间的距离,发生能量转移,使荧光信号在一定程度上被淬灭。在优化的条件下,我们使用该传感器对汞离子进行检测,动力学响应范围为50nM到1000nM,线性相关方程为y= 5281.13 - 1650.56 lg[Hg2+] ( R2 = 0.985),检测下限为79nM。此外,我们还考察了该传感器的选择性,当用其它干扰离子（浓度都为1.0µM）代替待测离子进行实验时,没有发生明显的荧光淬灭,说明该传感器具有较高的选择性。该传感器的构建为汞离子的检测提供了一条快速、简便的新途径。     

Preparation of Cu (II) imprinted polymer electrode and its application for potentiometric and voltammetric determination of Cu (II)

The Cu (II) imprinted polymer glassy carbon electrode (GCE/Cu-IP) was prepared by electropolymerization of pyrrole at GCE in the presence of methyl red as a dopant and then imprinting by Cu²⁺ ions. This electrode was applied for potentiometric and voltammetric detection of Cu²⁺ ion. The potentiometric response of the electrode was linear within the Cu²⁺ concentration range of 3.9 × 10^?6 to 5.0 × 10^?2 M with a near-Nernstian slope of 29.0 mV decade^?1 and a detection limit of 5.0 × 10^?7 M. The electrode was also used for preconcentration anodic stripping voltammetry and results exhibited that peak currents for the incorporated copper species were dependent on the metal ion concentration in the range of 1.0 × 10^?8 to 1.0 × 10^?3 M and detection limit was 6.5 × 10^?9 M. Also the selectivity of the prepared electrode was investigated. The imprinted polymer electrode was used for the successful assay of copper in two standard reference material samples.     

Voltammetric Sensing of Trace Metals at a Poly(pyrrole‐malonic acid) Film Modified Carbon Electrode

The oxidative electropolymerization of the (3‐pyrrol‐1‐ylpropyl)malonic acid monomer 1 is a simple and reproducible one‐step procedure for the synthesis of complexing polymer film modified electrodes, which have been applied to the electroanalysis of Cu(II), Pb(II), Cd(II) and Hg(II) ions by preconcentration upon complexation, followed by anodic stripping analysis. The detection limits were determined from square‐wave voltammetry at 0.5 nM, 5 nM, 50 nM and 0.2 μM for Pb(II), Cu(II), Hg(II) and Cd(II), respectively, after 10 min preconcentration. The modified electrodes showed a better selectivity toward copper(II) ions. Analysis of copper in a tap water sample agreed well with ICPMS analysis results.     

A Novel Fluorescent Aminoacid Designed for Fluorometric Detection of Cu （Ⅱ）

A fluorescent aminoacid was designed for selective and sensitive detection of Cu(II) in aqueous solution. The designing of this Cu(II) fluorescent chemosensing molecule, N ± (1‐naphthyl). aminoacetic acid (NAA), was based on the binding of Cu(II) to aminoacetic acid and the novel charge transfer photophysics of 1‐aminonaphthalenes. The fluorescence of NAA was found quenched by Cu (II) and several other metal ions of similar electronic structure such as Co(II), Ni(II) and Zn(II). The quenching was shown to occur via electron transfer within the metal‐NAA complex, which required an optimal combination of high binding affinity and favorable redox properties of the components in the metal‐NAA complex and hence afforded selective fluorometric detection of Cu(II). The calibration graph obeyed Stern‐Volmer theory and was shown for Cu(II) over the range of 0–2.75 ± 10–⁴ mol/L. The quenching constant of Cu(II) was measured as 8.0 ± 10³ mol/L that was two orders of magnitude higher than those of Co(II), Ni(II) and Zn(II). The 3SD limit of detection for Cu(II) was 8.00 ± 10^?6 mol/L with a coefficient of variation of 1.65%. Linear range for quantitative detection of Cu(II) was 2.67 ± 10^?5‐2.75 ± 10^?4 mol/L. The method was applied to synthetic sample measurements which gave recoveries of 105%‐112%.     

Calix[4]pyrrole virtuous sensor: a selective and sensitive recognition for Pb(II) ions by spectroscopic and computational study

A novel supramolecular sensor derived from calix[4]pyrrole system i.e. calix[4]pyrrole bearing aminoanthraquinone derivative (CAAQ) have been designed and synthesized. The complexation behavior of metal cations [Ag(I), Ba(II), Ca(II), Ni(II), Co(II), Fe(III), Hg(II), Cu(II), Cr(II), Pb(II), Zn(II), (1 × 10^?4 M)] with CAAQ (1 × 10^?6 M) was studied by spectrophotometry and spectrofluorometry. Metal ion like Pb(II) produces red shift in absorption spectra and quenching in emission spectra likelihood of strong complexation of Pb(II) ions with CAAQ. Fluorescence cell imaging also supports the complexation of Pb(II) ions with CAAQ. The binding constants, quantum yield, stoichiometry of complex, mechanism of quenching by Stern–Volmer equation and Density functional theory calculation have been determined.     

Construction and Application of an Electrochemical Sensor for Simultaneous Determination of Cd(II), Cu(II) and Hg(II) in Water and Foodstuff Samples

By incorporation of synthesized magnetite nanoparticles (Fe₃O₄ NPs) coated with a new Schiff base into carbon paste electrode, a novel modified electrode was constructed for simultaneous determination of ultra trace amounts of Cd(II), Cu(II) and Hg(II). The complexation reaction of Schiff base with metal ions was studied spectrophotometrically. Under optimal conditions a detection limit of 0.20, 0.90 and 1.00 ng mL^?1 for Cd(II), Cu(II) and Hg(II), respectively, was obtained. We take the advantages of the proposed method for simple, rapid, sensitive and selective simultaneous determination of trace amounts of hazardous Cd(II), Cu(II) and Hg(II) in water and foodstuff samples.     

Highly Selective and Sensitive Membrane Sensors for Copper(II) Ion Based on a New Benzo‐Substituted Macrocyclic Diamide 6,7,8,9,10‐Hexahydro‐2H‐1,13,4,7,10‐benzodioxatriazacyclopentadecine‐3,11(4H,12H)‐dione

Novel PVC membrane (PME) and coated graphite (CGE) Cu²⁺‐selective electrodes based on 5,6,7,8,9,10‐hexahydro‐2H‐1,13,4,7,10‐benzodioxatriazacyclopentadecine‐3,11(4H,12H)‐dione are prepared. The electrodes reveal a Nernstian behavior over wide Cu²⁺ ion concentration ranges (1.0×10^?7–1.0×10^?1 M for PME and 1.0×10^?8–1.0×10^?1 M for CGE) with very low limits of detection (7.8×10^?8 M for PME and 9.1×10^?9 M for CGE). The potentiometric responses are independent of the pH of the test solutions in the pH range 2.7–6.2. The proposed electrodes possess very good selectivities for Cu²⁺ over a wide variety of the cations including alkali, alkaline earth, transitions and heavy metal ions. The practical utility of the proposed electrodes have been demonstrated by their use in the study of interactions between copper ions and human growth hormone (hGH) in biological systems, potentiometric titration of copper with EDTA and determination of copper content of a sheep blood serum sample and some other real samples.     

Simultaneous Voltammetric Determination of Zn(II), Pb(II), Cu(II), and Hg(II) in Ethanol Fuel Using an Organofunctionalized Modified Graphite‐Polyurethane Composite Disposable Screen‐Printed Device

A disposable screen‐printed device containing working, auxiliary, and reference electrodes is proposed for the simultaneous voltammetric determination of Zn(II), Pb(II), Cu(II), and Hg(II) in ethanol fuel. The working electrode was printed using an ink modified with 2‐benzothiazole‐2‐thiol organofunctionalized SBA‐15 silica, in order to increase sensitivity. The performance of this electrode was compared with that of bare and SBA‐15‐modified electrodes. After optimizing the experimental parameters, the device was applied in determination of the analytes in commercial ethanol fuel samples, using 0.10 mol L^?1 KCl/ethanol ratios of 30 : 70 (v/v), with [H⁺]=10^?5 mol L^?1. After 5 min of preconcentration at ? 1.3 V (vs. pseudo‐Ag/AgCl), four well‐resolved signals were obtained, enabling simultaneous determination of the four analytes using a differential pulse anodic stripping voltammetry (DPASV) procedure. The limits of detection were 0.30, 0.065, 0.030, and 0.046 µmol L^?1 for Zn(II), Pb(II), Cu(II), and Hg(II), respectively. The results of these analyses were in agreement with those obtained using graphite furnace atomic absorption spectroscopy (GFAAS) for Pb(II), Cu(II), and Hg(II), and high‐resolution continuum source flame atomic absorption spectrometry (HR‐CS‐FAAS) for Zn²⁺, at a 95 % confidence level. Analytes originally present in the samples could be detected, and the interference of some cations and anions was evaluated.     

Poly(N‐acetyl‐α‐acrylic acid): Synthesis,Characterization and Chelation Properties through Liquid Phase Polymer‐Based Retention Technique

The synthesis and characterization of the water‐soluble poly(N‐acetyl‐α‐acrylic acid) by radical polymerization were carried out. The polymer was characterized by Fourier Transform Infrared (FT‐IR), ¹H NMR and ¹³C NMR spectroscopies, and thermogravimetric analysis (TGA). The metal ion binding properties for the metals Cu(II), Co(II), Ni(II), Cd(II), Zn(II), Pb(II), Hg(II), Cr(III) in the aqueous phase were studied using the liquid‐phase polymer‐based retention technique. The metal ion interactions with the hydrophilic polymer were determined as a function of pH and of the filtration factor. The polychelatogen showed a high affinity for metal ions and higher selectivity for Cr(III) at pH = 3.     

Determination of Pb(II) and Cu(II) by Electrothermal Atomic Absorption Spectrometry after Preconcentration by a Schiff Base Adsorbed on Surfactant Coated Alumina

1,2-Bis（salicylidenamino）ethane loaded onto sodium dodecyl sulfate-coated alumina was used as a new chelating sorbent for the preconcentration of traces of Pb（Ⅱ） and Cu（Ⅱ） prior to atomic absorption spectrometric determination. The influence of pH, flow rates of sample and eluent solutions, and foreign ions on the recovery of Pb（Ⅱ） and Cu（Ⅱ） by this sorbent has been studied. The retained ions were eluted with 4 mol·L nitric acid and determined by electrothermal atomic absorption spectrometry （ETAAS）. The data of limit of detection （3σ） for Pb（Ⅱ） and Cu（Ⅱ） were found to be 8.57 and 2.69 ng·L^-1 respectively, while the enrichment factor for both ions was 100. The proposed method was successfully applied to determination of lead and copper in different water samples.     

A Selective Film Based on Poly(3‐octylthiophene) Doped with Dihydroxyanthraquinone Sulfonate

A stable film of poly(3‐octylthiophene)–dihydroxyanthraquinone sulfonate has been synthesized electrochemically in non‐aqueous solution. The incorporation of dihydroxyanthraquinone sulfonate as an anionic complexing ligand into poly(3‐octylthiophene) film during electropolymerization was achieved and copper ions were accumulated by reduction on the electrode surface. The presence of dihydroxyanthraquinone sulfonate during the electrochemical polymerization of 3‐octylthiophene is shown to impact the sensitivity and the stability of the organic conducting film electrode response. The electroanalysis of copper(II) ions using conducting polymer electrode was achieved by differential pulse anodic stripping voltammetry with remarkable selectivity. The analytical performance was evaluated and linear calibration graphs were obtained in the concentration range of 50–400 ng mL^?1 copper(II) ion for 240 seconds accumulation time and the limit of detection was found to be 7.8 ng mL^?1. To check the selectivity of the proposed stripping voltammetric method for copper(II) ion, various metal ions as potential interferents were tested. The developed method was applied to copper(II) determination in certified reference material, NWRI‐TMDA‐61, trace elements in fortified water.     

Preparation of polymer-coated electrodes containing metal ions complexing sites by electropolymerization of 2-mercaptobenzimidazole and 2-mercaptobenzothiazole on glassy carbon

The possibility of producing polymer-coated electrodes containing complexing agents capable of collecting metal ions was investigated. The organic ligands 2-mercaptobenzimidazole and 2-mercaptobenzothiazole were used as monomers for electropolymerization on glassy carbon electrodes. The electroanalytical applicability of the modified electrodes was evaluated for Hg²⁺ ions, by applying a chemical preconcentration step with subsequent measurement by differential pulse voltammetry. The influence of some electropolymerization parameters, such as scan rate, monomer concentration and the number of cyclic scans, on the voltammetric response of mercury(II) was studied. A 5 min preconcentration period allowed the detection of 0.08 mg/L (4.0 × 10⁻⁷ mol L⁻¹) mercury.     

Unsymmetrical Tetradentate Schiff Bases Copper (II) Complex as Neutral Carrier for Thiocyanate‐Selective Electrode

Abstract

Three kinds of transition metal chelates of unsymmetrical tetradentate Schiff base, o‐hydroxybenzophenone‐1,2‐diaminobenzene‐pyrrole‐2‐carbaldehyde(H₂L), were synthesized to prepare anion‐selective electrodes and their anion response characteristics were investigated. The results show that the performances of the electrodes are considerably influenced by the nature of the central metals. The proposed electrode with the Cu(II)‐chelate and cationic additive demonstrated an anti‐Hofmeister selectivity sequence with a good selectivity towards thiocyanate in the following order: Thiocyanate>iodide>salicylate>perchlorate>bromide>nitrite>chloride>acetate>fluoride>nitrate>sulfite>sulfate. The electrode had an excellent linear response to thiocyanate from 3.4×10^?7 to 1.0×10^?1 M in phosphate buffer solution at pH 5.0 with a slope of ?58.7 mV per decade, a detection limit of 1.6×10^?7 M, and a fast response time within 5 s over the entire concentration series. Spectroscopic techniques and AC impedance were used to investigate the response mechanism to thiocyanate of the membrane doped with Cu(II)‐chelate. The preliminary application of the electrode for determination of thiocyanate in wastewater and urine samples is reported.     

Binding of Copper(II) to Pectins by Electrochemical Methods

The interaction between Cu(II) and pectin extracted from citrus fruit was studied in KNO₃ 0.10 mol dm^?3 at 25 °C and pH 5.5, using ion selective electrode potentiometry and voltammetry, namely differential pulse polarography and square‐wave voltammetry. Although many independent variables may affect Cu(II)‐polymer interactions such as charge density, polymer concentration and copper to polymer concentration ratio, a good fitting was observed for the model with ML and ML₂ complex species, when M:L total concentration (mol dm^?3) ratio varies from 0.2 to 2.7 and the ligand concentration is in the range (0.2 to 1) g dm^?3, i.e., (0.4 to 2)×10^?3 mol COO^? dm^?3. The complex parameters found in these conditions were log β_CuL=3.5±0.1 and log β_CuL2= 8.0±0.2. For lower total ligand and total metal ion concentrations, used in voltammetry, the interaction Cu(II)‐pectin is affected by a cooperative mode (increase of metal ion‐ligand affinity) when the total metal ion concentration increases and by an anti‐cooperative mode when the total ligand concentration increases, possibly due to different conformations of the polymer.     

Electrochemical performance of a three-layer electrode based on Bi nanoparticles,multi-walled carbon nanotube composites for simultaneous Hg(II) and Cu(II) detection

Electrochemical analysis is a promising technique for detecting biotoxic and non-biodegradable heavy metals. This article proposes a novel composite electrode based on a polyaniline (PANi) framework doped with bismuth nanoparticle@graphene oxide multi-walled carbon nanotubes (Bi NPs@GO-MWCNTs) for the simultaneous detection of multiple heavy metal ions. Composite electrodes are prepared on screen-printed electrodes (SPCEs) using an efficient dispensing technique. We used a SM200SX-3A dispenser to load a laboratory-specific ink with optimized viscosity and adhesion to draw a pattern on the work area. The SPCE was used as substrate to facilitate cost-effective and more convenient real-time detection technology. Electrochemical techniques, such as cyclic voltammetry and differential pulse voltammetry, were used to demonstrate the sensing capabilities of the proposed sensor. The sensitivity, limit of detection, and linear range of the PANi-Bi NPs@GO-MWCNT electrode are 2.57 × 10² μA L μmol⁻¹ cm⁻², 0.01 nmol/L, and 0.01 nmol/L–5 mmol/L and 0.15 × 10⁻¹ μA L μmol⁻¹ cm⁻², 0.5 nmol/L, and 0.5 nmol/L–5 mmol/L for mercury ion (Hg(II)) and copper ion (Cu(II)) detection, respectively. In addition, the electrode exhibits a good selectivity and repeatability for Hg(II) and Cu(II) sensing when tested in a complex heavy metal ion solution. The constructed electrode system exhibits a detection performance superior to similar methods and also increases the types of heavy metal ions that can be detected. Therefore, the proposed device can be used as an efficient sensor for the detection of multiple heavy metal ions in complex environments.     

Biofunctionalization of Multiwalled Carbon Nanotubes by Electropolymerized Poly(pyrrole‐concanavalin A) Films

The synthesis and electropolymerization of a pyrrolic concanavalin A derivative (pyrrole‐Con A) onto a multiwalled carbon nanotube (MWCNT) deposit is reported. Glucose oxidase was then immobilized onto the MWCNT‐poly(pyrrole‐Con A) coating by affinity carbohydrate interactions with the polymerized Con A protein. The resulting enzyme electrode was applied to the amperometric detection of glucose exhibiting a high sensitivity of 36 mA cm^?2 mol^?1 L and a maximum current density of 350 μA cm^?2.