Automated Determination of Cd^(2+) and Pb^(2+) in Natural Waters with Sequential Injection Analysis Device Using Differential Pulse Anodic Stripping Voltammetry

An electrochemical flow device has been developed for the determination of heavy metal ions(HMI)in water using multiwalled carbon nanotubes(MWCNTs)/Nafion(NA)/Hg electrode,by mean of diff erential pulse anodic stripping voltammetry coupled with sequential injection analysis.The accuracy of the determination was ensured by the great electrical conductivity of MWCNTs and the high adsorption capacity of Hg.NA was used for MWCNTs immobilization for the long-term application of the electrode.The mercury film was cleaned after determination and another one would form during deposition.A lower limit of detection and a wider determination range of Cd^(2+)and Pb^(2+)could be achieved using the automatically analytical device combining with the MWCNTs/NA/Hg-modified electrode.The real-time monitoring of Cd^(2+)and Pb^(2+)in fresh water using this device continued for 10 days.The results indicated that the method was potential for on-site and real-time determination of HMI in water samples.

Differential Pulse Anodic Stripping Voltammetric Determination of Lead with Heparin Modified Electrode

A novel differential pulse anodic stripping voltammetry for the determination of trace amounts of lead, using a biomacromolecule heparin drop-coated modified glassy carbon electrode, has been described. Pb2+ was deposited on the surface of a heparin-modified electrode at -1.0 V (vs. SCE) via forming Pb2+-heparin and subsequent re-duction at the electrode. In the following step, Pb-heparin was oxidized, and voltammograms were recorded by scanning the potential in a positive direction. Conditions were optimized with respect to the pH of the medium, the mass of drop-coated heparin, accumulation potential and accumulation time. The peak current was proportional to the Pb2+ concentration in the range of 2.0×10-9 to 7.0×10-7 mol/L. The detection limit was 3.0×10-10 mol/L. The relative standard deviation was 4.83% for 1.0×10-8 mol / L Pb2+ (n=10). The developed method has been applied to the determination of Pb2+ in water samples with satisfactory results.

Determination of Epinephrine Using Poly(Neutral Red)Modified Carbon Fibre Microelectrodes by Anodic Stripping Voltammetry

Poly(neutral red) film modified carbon fibre microelectrodes offer substantial improvement in voltammetric sensitivity and selectivity towards epinephrine (EP). The poly(neutral red) film was electropolymerized by cycling the potential between -0.8 V and +0.8 V. The anodic stripping voltammetric response for EP was found to be dependent on accumulation time and potential. By using a poly(neutral red) film modified carbon fibre microelectrode with a 1 min preconcentration at -1.2 V in biological phosphate buffer solution (pH=7.4), a good linear relationship between the anodic stripping peak currents and EP concentrations was obtained in the range of 2.0×10 -7 ￣ 2.0×10 -5 mol/L. The detection limit was up to 9.0 ×10 -8 mol/L. Moreover, 400 times higher concentrations of vitamin C did not interfere with the measurement of EP. This method was used for determining EP concentrations in epinephrine hydrochloride injection solution with satisfactory results.

Determination of Trace Thiocyanate by a Chitosan-Modified Glassy Carbon Electrode

A chitosan modified glassy carbon electrode(CMGCE) was employed for the determination of thiocyanate. The measurement was carried out by means of anodic stripping voltammetry. The effects of several experimental parameters, such as pH, the amount of modifier, deposition potential and deposition time were studied for analytical application, respectively. A liner response was obtained in the concentration range of 3 5×10 -8 - 9.3×10 -7 g/mL of SCN -. The detection limit was found to be 1.9×10 -8 g/mL. The method was satisfactorily used to detect SCN - in saliva.

Electrochemical Characteristics and Applications of Boron-Doped Polycrystalline Diamond Film Electrodes

The elcetrochemical characteristics of boron doped polycrystalline diamond thin film (BDF) electrode 4×4 mm 2 in size were studied using cyclic voltammetry and potentiostatic method. The diamond electrode exhibits adequate electrochemical activity and its response current changes linearly with K 3Fe(CN) 6 concentrations. The response current is proportional to the square root of the scan rate, reflecting mass transport controlled by planar diffusion. Stable mass transport can be quickly established within 4s. The BDF electrode provides good resolving power for the determination of lead and cadmium and gives satisfactory results in the analysis of pure water sample.

Simultaneous electrochemical DNA hybridization assay for PAT and FMV 35S gene sequence using quantum dots as labels

An electrochemical method for the simultaneous detection of two different DNA sequences from PAT and FMV 35S gene sequence using CdS and PbS quantum dots （QDs） as labels was described. The QDs were readily functionalized with oligonucleotides as electrochemical DNA probes and selectively hybridized to the complementary sequences immobilized on the microplate. The QDs anchored on the hybrids were dissolved in the solution by the oxidation of HNO3 and further detected by a sensitive differential pulse anodic stripping voltammetric method （DPASV）. The DPASV signals of the oxidation of Cd^2＋ and Pb^2＋ ions present in the solution were different and reflected the identity of corresponding ssDNA targets sequences.

Electrochemical Metalloimmunoassay Based on Enlargement of Gold Nanoparticle Label Treated with Ag Enhancement System

A novel sensitive electrochemical immunoassay with colloidal gold as the antibody labeling tag and subsequent signal amplification by silver enhancement is described. Colloidal gold was treated by a light-sensitive silver enhancement system which made silver deposit on the surface of colloidal gold(form Au/Ag core-shell structure), followed by the release of the metallic silver atoms anchored on the antibody by oxidative dissolution of them in an acidic solution and the indirect determination of the dissolved Ag + ions by anodic stripping voltammetry(ASV) at a carbon fiber microelectrode. The electrochemical signal is directly proportional to the amount of analyte(goat IgG) in the standard or a sample. The method was evaluated by means of a noncompetitive heterogeneous immunoassay of immunoglobulin G(IgG) with a concentration as low as 0.2 ng/mL. The high performance of the method is related to the sensitive ASV determination of silver(Ⅰ) at a carbon fiber microelectrode and to the release of a large number of Ag + ions from each silver shell anchored on the analyte(goat IgG).

SBA-15 Modified Carbon Paste Electrode for Rapid cTnI Detection with Enhanced Sensitivity

A novel electrochemical immunoassay for cardiac troponin Ⅰ （cTnI） combining the concepts of the dual monoclonal antibody ＂sandwich＂ principle, the silver enhancement on the nano-gold particle, and the SBA-15 mesoporous modified carbon paste electrode （SBA-MCPE） is described. Four main steps were carried out to obtain the analytical signal, i.e., electrode preparation, immunoreaction, silver enhancement, and anodic stripping voltammetric detection. A linear relationship between the anodic stripping peak current and concentration of cTnI from 0.5 to 5.0 ng/mL and a limit of detection of 0.2 ng/mL of cTnI were obtained.

Investigations of Thallium(Ⅰ) Underpotential Deposition on the Silver Rotating Disk Electrode and Its Analytical Application

The cyclic voltammetry(CV) and the square wave technique were used for the investigations of thallium(Ⅰ) underpotential deposition(UPD) on the silver electrode. A solution of 10 \{mmol/L\} HClO 4+10 mmol/L NaCl was selected as the supporting electrolyte. The calibration plots for Tl(Ⅰ) concentration in the range of 2×10 -9 -1×10 -7 mol/L were obtained. The detection limit was 5×10 -10 mol/L. For the solutions of 4 0×10 -9 mol/L thallium added before the urine sample pretreatment procedure, the average recovery was 105 6% with a relative standard deviation(RSD) of 15 5%.

Lead and Cadmium Distribution in Tubes of Galvanized Steel by Hot-Dip Used for Drinking Water Supply

The main objective of this work was to evaluate the presence of lead and cadmium in galvanized steel tubes by hot-dip used exclusively for drinking water supply.In this research,samples of galvanized tubes were removed from walls of residential buildings with 30 years of use.In the process of hot galvanizing,the manufacturing standards allow or for low cost conveniences,and the use of primary zinc ingot with 1.6%metallic impurities,such as lead and cadmium,is allowed,enabling the incorporation of these metals into the zinc coating deposited on the carbon steel.The associated corrosion of these tubes can release these toxic metals,contaminating the drinking water used by residents.The samples taken from the tubes were evaluated by a square-wave anodic stripping voltammetry technique,and the results for lead and cadmium suggested randomly distributed levels,indicating that the contents of these contaminants depend mainly on the quality of the added primary zinc and the operational conditions of the immersion bath.The metallographic evaluations performed on the samples of the galvanized tubes showed irregularities in thickness and even a lack of the zinc layer deposited on the carbon steel surface.These facts suggest that galvanized tubes should not be used for drinking water.

PSO-SVM applied to SWASV studies for accurate detection of Cd(II)based on disposable electrode

Square wave anodic stripping voltammetry(SWASV)is an effective method for the detection of Cd(II),but the presence of Pb(II)usually has some potential and negative interference on the SWASV detection of Cd(II).In this paper,a novel method was proposed to predict the concentration of Cd(II)in the presence of Pb(II)based on the combination of chemically modified electrode(CME),machine learning algorithms(MLA)and SWASV.A Bi film/ionic liquid/screen-printed electrode(Bi/IL/SPE)was prepared and used for the sensitive detection of trace Cd(II).The parameters affecting the stripping currents were investigated and optimized.The morphologies and electrochemical properties of the modified electrode were characterized by scanning electron microscopy(SEM)and SWASV.The measured SWASV spectrograms obtained at different concentrations were used to build the mathematical models for the prediction of Cd(II),which taking the combined effect of Cd(II)and Pb(II)into consideration on the SWASV detection of Cd(II),and to establish a nonlinear relationship between the stripping currents of Pb(II)and Cd(II)and the concentration of Cd(II).The proposed mathematical models rely on an improved particle swarm optimization-support vector machine(PSO-SVM)to assess the concentration of Cd(II)in the presence of Pb(II)in a wide range of concentrations.The experimental results suggest that this method is suitable to fulfill the goal of Cd(II)detection in the presence of Pb(II)(correlation coefficient,mean absolute error and root mean square error were 0.998,1.63 and 1.68,respectively).Finally,the proposed method was applied to predict the trace Cd(II)in soil samples with satisfactory results.

A voltammetric sensor for simultaneous determination of lead,cadmium and zinc on an activated carbon fiber rod

In this work, a simple, low cost and sensitive voltammetric sensor was developed for the simultaneous detection of lead （Pb2＋）, cadmium （Cd2＋）, and zinc （Zn2＋） ions based on a disposable carbon fiber rod （CFR）. The important factors to enhance the sensing property were creation of a clean surface by dealing with CFR at a high potential and electrochemical deposition of bismuth （Bi） film to improve the accumulation of heavy metal ions. The morphology and conductivity of such activated CFR was characterized by scanning electron microscopy and electrochemical impedance spectroscopy, respectively. In terms of application, differential pulse anodic stripping voltammetry （DPASV） was employed for the simultaneous detection of Pb2＋, Cd2＋, and Zn2＋ on Bi film-coated activated CFR. Experimental parameters, such as the pH value of buffer solution, stirring speed and enrichment factors were optimized. Under optimal conditions, the DPASV peak currents showed good linear relationships with Pb2＋, Cd2＋ and Zn2＋ concentrations in the range of 0.5-2.25 μg/L, 0.5-4.0 μg/L and 1.0- 4.0 μg/L with detection limits of 0.1, 0.3 and 1.0 μg/L （SIN = 3）, respectively. Finally, the proposed analysis system was successfully utilized for the simultaneous detection of Pb2＋, Cd2＋, and Zn2＋ contents in rice samples. This study indicated that Bi film-coated activated CFR based DPASV sensor can be a promising and reliable tool for rapid analysis of emergency Dollution affairs of heavv metal ions in food.

Underpotential Deposition Study and Determination of Bismuth on Gold Electrode by Using Voltammetry

The cyclic voltammetry (CV) and the semidifferential anodic stripping voltammetry (SdASV) were used for investigation of bismuth(III) underpotential deposition (UPD) on gold electrode. Based on the excellent electrochemical properties of Au/Bi UPD system, a new method for determining bismuth(III) was established. A solution of 0.1 mol/L HNO 3 was selected as the supporting electrolyte. Factors affecting the Bi(III) UPD and stripping steps were investigated and an optimized analytical procedure was developed. The calibration plots for Bi(III) concentration in the range 1.25×10 -8 -1.0×10 -7 mol/L were obtained. The detection limit, calculated as three times the standard deviation of the analytical signal of 8.3×10 -8 mol/L for a 90 s electrodeposition at 0.00 V (while the solution magnetically stirred at a speed of 300 rpm), was 7.5×10 -9 mol/ L. For 8 successive determinations of 1.25×10 -7 mol/L Bi(III), the obtained RSD (relative standard deviation) was 0.4%. The developed method was applied to bismuth determining in medicine and urine samples. The analytical results were compared with that of atomic emission spectrometry (AES) method.

Ultrasensitive electrochemical immunosensor of carcinoembryonic antigen based on gold-label silver-stain signal amplification

A novel gold-label silver-stain electrochemical immunosensor was developed based on polythioninegold nanoparticles（PTh-Au） modified glassy carbon electrode（GCE） as a platform and secondary antibody labeled Au NPs（Ab;-Au） as immumoprobe for carcinoembryonic antigen（CEA） detection. The sandwich-type biosensor adopted anodic stripping voltammetry to detect silver stripping signal when the Ab;-Au of the formed immunocomplexes were stained with silver. The optimized detection conditions were investigated. The effect of different electrochemical responses at various concentrations of CEA was checked by anodic stripping voltammetry. This immunosensor showed a low detection limit of 0.055 ng/mL and a wide linear calibration of 0.1-120 ng/mL（R;=0.99856）. Moreover, this immunoassay also existed the advantages of good reproducibility, stability and selectivity. Thus, this immunosensing protocol may provide a potential application for effective clinical detection of CEA.

Graphene-platinum nanocomposite as a sensitive and selective voltammetric sensor for trace level arsenic quantification

A simple protocol for the chemical modification of graphene with platinum nanoparticles and its subsequent electroanalytical application toward sensitive and selective determination of arsenic has been described.Chemical modification was carried out by the simultaneous and sequential chemical reduction of graphene oxide and hexachloroplatinic acid in the presence of ethylene glycol as a mild reducing agent.The synthesized graphene-platinum nanocomposite(Gr-nPt)has been characterized through infrared spectroscopy,x-ray diffraction study,field emission scanning electron microscopy and cyclic voltammetry(CV)techniques.CV and square-wave anodic stripping voltammetry have been used to quantify arsenic.The proposed nanostructure showed linearity in the concentration range 10-100 nM with a detection limit of 1.1 nM.The proposed sensor has been successfully applied to measure trace levels of arsenic present in natural sample matrices like borewell water,polluted lake water,agricultural soil,tomato and spinach leaves.

Sensitive Voltammetric Detection of Trace Heavy Metals in Real Water Using Multi-Wall Carbon Nanotubes/Nafion Composite Film Electrode

Multi-wall carbon nanotubes （MWCNTs） and Nation composite film （MWCNTs/Nafion） were used for fabricating electrochemical sensors for the voltammetric detection of trace lead（Ⅱ） and cadmium（Ⅱ） in several water samples. The morphology and structure of MWCNTsfNafion film were characterized by scanning electron microscopy （SEM） and infrared spectrum （IR）. The electron transfer of MWCNTs/Nafion composite film was examined by cyclic voltammetry （CV） and electrochemical impedance spectrum （EIS）. Various experimental parameters, which influenced the response of MWCNTs/Nation/GC to target metals, were optimized. The results showed that the synergistic effect was obtained on the MWCNTs/Nafion/GC whose sensitivity and stability were better than those of Nation-coated electrode （Nafion]GC） or CNTs/GC. Stability of the Pb（II） and Cd（Ⅱ） stripping signals was excellent with relative standard deviations （RSD） within 5% （n = 10） from one electrode preparation to another, and RSD of 30μg.L^1 Pb（Ⅱ） and Cd（Ⅱ） were 2.8% and 3.2% for 20 repeated analysis on one single CNTs/Nafion/GC. Over 50 runs, the stability of Pb and Cd detection at the MWCNTs/Nafion conposites electrode was still satisfactory with RSD lower than 6.0%. The determination limits （S/N=3） of the proposed method were determined to be 100 ng·L^-1 for Pb and 150 ng.L^-1 for Cd. Finally, the MWCNTs/Nafion/GC was successfully applied to determine Pb（Ⅱ） and Cd（Ⅱ） in different water samples with recoveries of 97%-103% for Pb and 96%-104% for Cd.

A new static induction thyristor with high forward blocking voltage and excellent switching performances

A new static induction thyristor （SITH） with a strip anode region and p- buffer layer structure （SAP-B） has been successfully designed and fabricated. This structure is composed of a p- buffer layer and lightly doped n- regions embedded in the p＋-emitter. Compared with the conventional structure of a buffed-gate with a diffused source region （DSR buffed-gate）, besides the simple fabrication process, the forward blocking voltage of this SITH has been increased to 1600 V from the previous value of 1000 V, the blocking gain increased from 40 to 70, and the turn-offtime decreased from 0.8 to 0.4μs.

Application of a wedge strip anode in micro-pattern gaseous detectors

The wedge strip anode （WSA） has been widely used in 2-D positiomsensitive detectors. A circular WSA with an effective diameter of 52 mm is successfully coupled to a tripe gas electron multiplier （GEM） detector through a simple resistive layer. A spatial resolution of 440 μm （FWHM） is achieved for a 10 kVp X-ray using 1 atm Ar：CO2=70：30 gas. The simple electronics of only three channels makes it very useful in applications strongly requiring simple interface design, e.g. sealed tubes and high pressure detectors.