Cadmium determination in phosphate fertiliser using a PAN-Nafion® modified glassy carbon electrode by stripping voltammetry

A simple method for the determination of trace cadmium (Cd) (II), using a disposable 1-(2-pyridylazo)-2-naphthol [PAN]-Nafion®-coated glassy carbon electrode, has been developed. The modified electrode exhibited a significant improvement on both sensitivity and selectivity for Cd (II) determination, compared with a bare glassy carbon electrode (GCE), a PAN-coated GCE (PAN-GCE), and a Nafion®-coated GCE (Nafion® GCE). Differential pulse anodic stripping voltammetry (DPASV) was performed, in 0.05?M potassium hydrogen phthalate (KHP) buffer medium, after Cd (II) ion accumulation. The Cd(II) ion accumulated on the PAN-Nafion® surface of the glassy carbon working electrode through the formation of a chemical complex at an open circuit. The modified GCE with Cd (II) complex was then transferred to a 0.1?M KI solution and subjected to an electrochemical stripping procedure. Cyclic voltammetry (CV) was employed to confirm the successful stepwise assembly procedure for the modified electrode. The structure of PAN-Nafion® on the surface-modified electrode was characterised by scanning electron microscopy (SEM). System variables were optimised to yield the most suitable conditions, including the pH and concentration of the accumulation medium, deposition potential, deposition time, and amount of coated PAN-Nafion®. The quantitative analysis of contaminated cadmium in phosphate fertiliser samples was performed. The results obtained from the proposed method agree well with those obtained by inductively coupled plasma-optical emission spectrophotometry (ICP-OES).     

Determination of tryptophan and histidine by adsorptive cathodic stripping voltammetry using H-point standard addition method

A sequential method is proposed for the determination of tryptophane and histidine by adsorptive cathodic stripping voltammetry using standard addition and H-point standard addition method (HPSAM). The complexes of copper(II) with the amino acids were accumulated onto the surface of a hanging mercury drop electrode for 60 s. Then the preconcentrated complexes were reduced by square wave voltammetry and the peak currents were measured. The effect of various parameters such as pH, concentration of copper, accumulation potential, accumulation time and scan rate on the sensitivity were studied by one-at-a time and artificial neural network. Under the optimized conditions, the peak currents at about +0.05 to −0.30 V is proportional to the concentration of tryptophan and histidine over the concentration ranges of 5–220 and 100–1200 nM, respectively. Optimization of the parameters by one-at-a time showed that at accumulation potential of 0.10 V (versus Ag/AgCl reference electrode) the peak current is proportional only to the concentration of tryptophan and histidine does not have any contribution to the current. The optimization results by artificial neural network showed that at accumulation potential of −0.06 V (versus Ag/AgCl) the peak current is proportional to the both concentrations of tryptophan and histidine. Therefore, the method of H-point standard addition has been used for resolving overlap voltamograms for determination of histidine in the present of tryptophane. The method was successfully applied to the determination of tryptophan and histidine in synthetic and real samples.     

Fabrication of Bismuth/Multi-walled Carbon Nanotube Composite Modified Glassy Carbon Electrode for Determination of Cobalt

A bismuth/multi‐walled carbon nanotube (Bi/MWNT) composite modified electrode for determination of cobalt by differential pulse adsorptive cathodic stripping voltammetry is described. The electrode is fabricated by potentiostatic pre‐plating bismuth film on an MWNT modified glassy carbon (GC) electrode. The Bi/MWNT composite modified electrode exhibits enhanced sensitivity for cobalt detection as compared with the bare GC, MWNT modified and bismuth film electrodes. Numerous key experimental parameters have been examined for optimum analytical performance of the proposed electrode. With an adsorptive accumulation of the Co(II)‐dimethylglyoxime complex at ?0.8 V for 200 s, the reduction peak current is proportional to the concentration of cobalt in the range of 4.0×10^?10?1.0×10^?7 mol/L with a lower detection limit of 8.1×10^?11 mol/L. The proposed method has been applied successfully to cobalt determination in seawater and lake water samples.     

Differential pulse anodic stripping voltammetric determination of traces of copper with a tobramycin-Nafion modified electrode.

A Nafion-modified glassy carbon electrode incorporated with tobramycin for the voltammetric stripping determination of Cu2+ has been explored. The electrode was fabricated by tobramycin containing Nafion on the glassy carbon electrode surface. The modified electrode exhibited a significantly increased sensitivity and selectivity for Cu2+ compared with a bare glassy carbon electrode and the Nafion modified electrode. Cu2+ was accumulated in HAc-NaAc buffer (pH 4.6) at a potential of -0.6 V (vs. SCE) for 300 s and then determined by differential pulse anodic stripping voltammetry. The effects of various parameters, such as the mass of Nafion, the concentration of tobramycin, the pH of the medium, the accumulation potential, the accumulation time and the scan rate, were investigated. Under the optimum conditions, a linear calibration graph was obtained in the concentration range of 1.0 x 10(-9) to 5.0 x 10(-7) mol l(-1) with a correlation coefficient of 0.9971. The relative standard deviations for eight successive determinations were 4.3 and 2.9% for 1.0 x 10(-8) and 2.0 x 10(-7) mol l(-1) Cu2+, respectively. The detection limit (three times signal to noise) was 5.0 x 10(-10) mol l(-1). A study of interfering substances was also performed, and the method was applied to the direct determination of copper in water samples, and also in analytical reagent-grade salts with satisfactory results.     

Stripping Analysis of Trace Arsenic Based on the MnOx/AuNPs Composite Film Modified Electrode in Alkaline Media

A simple, rapid fabricated and sensitive modified electrode for detection of As(III) in alkaline media was proposed. The modified electrode was prepared by co‐electrodeposition of manganese oxides (MnO_x) and gold nanoparticles (AuNPs) on the glassy carbon electrode (GCE) with cyclic voltammetry. Linear sweep anodic stripping voltammetry (LS‐ASV) was employed for the determination of arsenic (III) without interference from Cu(II), Hg(II), and other coexisting metal ions. A lower detection limit of 0.057 µg L^?1 (S/N=3) were obtained with a accumulation time of 200 s. The proposed method was successfully applied to determine arsenic (III) in real water samples with satisfactory recoveries.     

Voltammetry determination of trace manganese with pretreatment glassy carbon electrode by linear sweep voltammetry

This paper described the determination of trace manganese using linear sweep voltammetry at a pretreatment glassy carbon electrode. The glassy carbon electrode pretreated by electrochemical method in the 0.1 mol l⁻¹ NaOH solution greatly improved the electrode responsibility in the determination of manganese(II). The barrier to the detection of low manganese concentration was overcome by means of autocatalytic effect of manganese oxide deposited on the electrode in advance. Under the optimum experiments condition (0.04 mol l⁻¹ NH₃-NH₄Cl buffer solution, pH 9.0), the linear range was 4×10⁻⁸ to 1×l0⁻⁶ mol l⁻¹ Mn(II) for linear sweep voltammetry and 1×10⁻⁹ to 4×10⁻⁸ mol l⁻¹ Mn(II) for convolution voltammetry. The relative standard deviation for 2×10⁻⁸ mol l⁻¹ Mn(II) is 3.4%. The proposed method is simple, rapid, sensitive and selective. It had been applied to the determination of trace manganese in samples with satisfactory results.     

Determination of levofloxacin in human urine by adsorptive square-wave anodic stripping voltammetry on a glassy carbon electrode

The adsorption behavior of levofloxacin on a glassy carbon electrode was explored by cyclic and square-wave voltammetry. The drug was accumulated on a glassy carbon electrode and a well-defined oxidation peak was obtained in acetate buffer pH 5.0. Using square-wave anodic stripping voltammetry and accumulation at +0.4 V versus Ag/AgCl (saturated KCl) for 300 s, linear calibration graph was obtained from 6.0x10(-9) to 5.0x10(-7) M levofloxacin. The detection limit was calculated to be 5.0x10(-9) M. The R.S.D. determined from ten determinations at the 1.0x10(-7) M level was 1.7%. The method was applied for the direct determination of levofloxacin in diluted urine samples. It was validated using high-performance liquid chromatography (HPLC) as a reference method.     

Selective determination of Ni(II) and Co(II) by flow injection analysis and adsorptive cathodic stripping voltammetry on a wall jet mercury film electrode

Ni(II) and Co(II) have been determined simultaneously by means of adsorptive cathodic stripping voltammetry (AdCSV) in a computerised flow injection system. The working electrode was a glassy carbon disk that was fitted in a wall-jet flow cell. The electrode was initially electrochemically coated with a mercury film at -1.0 V by injecting a Hg(II) solution in the flow stream. Then, the sample, containing Ni(II) and Co(II), was mixed on-line with a solution containing dimethylgyoxime (DMG) at pH 9 in order to selectively complex the metal ions and was injected in the flow system. After a number of successive injections during which accumulation took place under controlled potentiostatic conditions, the surface-bound complexes were reduced in ammonia buffer at pH 9 by a cathodic scan of the potential of the working electrode in the square wave mode and the current-potential response was recorded. Finally, the electrode surface was regenerated by a potentiostatic polarisation at -1.4 V in the same buffer. The apparatus could be easily converted for continuous flow accumulation in order to increase the sensitivity; in this mode of operation, instead of performing discrete injections, the sample was continuously pumped through the cell. Various parameters associated with the preconcentration, stripping and regeneration steps were optimised for the determination of Ni(II) and Co(II). The selectivity of the method was demonstrated for the analysis of high purity iron; the accuracy for the determination of Ni(II) and Co(II) was 11 and 3%, respectively while the coefficient of variation was 10 and 8%, respectively.     

Manganese detection in marine sediments: anodic vs. cathodic stripping voltammetry

Three different electroanalytical techniques for the detection of manganese in marine sediments are evaluated. The anodic stripping voltammetry of manganese at an in situ bismuth-film-modified boron-doped diamond electrode and cathodic stripping voltammetry at a carbon paste electrode are shown to lack the required sensitivity and reproducibility whereas cathodic stripping voltammetry at a bare boron-doped diamond electrode is shown to be reliable and selective with a limit of detection, from applying a 60 s accumulation period of 7.4 × 10⁻⁷ M and a sensitivity of 0.24 A M⁻¹. The method was used to evaluate the manganese content of marine sediments taken from Šibenik, Croatia.     

Application of Square Wave Anodic Stripping Voltammetry for Determination of Traces of Ti(I) at Carbon Electrodes In Situ Modified with Bi Films

Bismuth films deposited in situ at glassy carbon and carbon film electrodes were tested for the determination of traces of Tl(I) separately and together with Zn(II) and Pb (II), in acetate buffer solution pH 3.7, using square wave anodic stripping voltammetry. Electrochemical impedance spectra in the presence of Tl(I) showed differences between the electrode substrates. The sensitivity to Tl does not depend on the presence of other ions, and was better at carbon film electrodes, although the 2 nmol L^?1 detection limit was independent of electrode substrate. Application to the measurement of Tl(I) in commercial berry juice is demonstrated.     

Determination of trace amounts of dipyridamole by stripping voltammetry using a Nafion modified electrode

This paper presents a new method for determination of dipyridamole by anodic stripping voltammetry using a Nafion modified glassy carbon electrode. The stripping peak current was proportional to the concentration of dipyridamole over the range of 1.0 x 10(-9)-8.0 x 10(-8) M in (pH 1.7) BrittondashRobinson buffer with 1 min accumulation. The detection limit has been estimated as 8.0 x 10(-11) M with 4 min accumulation. The method has been successfully applied to the determination of dipyridamole in human serum.     

聚赖氨酸/多壁碳纳米管修饰电极测定大米中的铅

通过滴涂及电聚合方式分别将多壁碳纳米管和赖氨酸共修饰于玻碳电极上,制备出聚赖氨酸/多壁碳纳米管修饰电极,并建立了阳极溶出伏安法测定铅离子的新方法。采用线性扫描伏安法及循环伏安法研究了铅离子在修饰电极上的电化学行为,并考察了测定底液、底液p H值、富集电位、富集时间等条件的影响。在最佳实验条件下,铅离子的溶出峰电流与其浓度在2.0×10-7~8.0×10-5mol·L-1范围内呈良好的线性关系,检出限为1.0×10-7mol·L-1。利用所制备的修饰电极对大米样品进行加标回收实验,回收率为98%~102%。该方法具有良好的灵敏度和稳定性,已成功应用于大米样品中铅离子的测定。     

Voltammetric determination of traces of cobalt(II) with a chemically modified carbon paste electrode

Summary A new preconcentration and voltammetric determination method for cobalt(II) in aqueous solution with a chemically modified electrode is proposed. The accumulation behaviour and voltammetry of cobalt(II) has been investigated with a carbon paste electrode modified with cationexchanger and 1,10-phenanthroline. The electrochemical response is characterized with respect to carbon paste composition, pH, preconcentration time, cobalt(II) concentration and other variables. For a 3-min preconcentration time, the electrode gives good linearity for 1×10^–7 to 4×10^–6 mol/l Co(II), a detection limit of 8×10^–8 mol/l. The response can be reproduced with a 4.0% relative standard deviation. The method is fairly free from many coexisting ions interferences. A rapid and convenient renewal procedure allows the use of a single electrode in multiple analytical determinations over several days. Satisfactory results are obtained for the determination of cobalt in a variety of certified standard reference materials.     

Simultaneous determination of chromium(III) and cadmium(II) by differential pulse anodic stripping voltammetry on a stannum film electrode

A stannum film electrode has been developed for the simultaneous determination of trace levels of chromium(III) and cadmium(II) by differential pulse anodic stripping voltammetry (DPASV). The stannum film electrode was generated in situ by depositing simultaneously the stannum film and the metals obtained by reduction of Cd(II) and Cr(III) at −1.4 V on a glassy carbon electrode. Then, the reduced products were oxidized by scanning the potential of the electrode from −1.4 to −0.4 V using DPASV. The electrode exhibited well-defined and separated stripping signals for both metals accompanied with a low background contribution. The possible mechanism of this design was proposed. Under the optimized working conditions, the detection limit was 2.0 and 1.1 μg l⁻¹ for Cr(III) and Cd(II) at a deposition time of 3 min. Finally, the stannum film electrode was successfully applied to the determination of Cd(II) in tap water with satisfactory results.     

Differential Pulse Adsorptive Stripping Voltammetric Determination of Chlorpyrifos at a Sepiolite Modified Carbon Paste Electrode

Abstract

An adsorptive stripping voltammetric (AdSV) method for the determination of organophosphorus insecticide chlorpyrifos at a bare carbon paste electrode (CPE) and clay modified carbon paste electrode (CMCPE) was developed. A systematic study of various experimental conditions, such as the pH, accumulation variables and composition of a modifier on the adsorptive stripping response, were examined by using differential pulse voltammetry. A significant improvement was observed in the sensitivity by using the present method with CMCPE. When CMCPE was used, a linear response was obtained over the concentration range 0.0001–2.0 ppm with lower detection limit of 0.00008 ppm, at an accumulation time of 80 s. The interference from other herbicides and ions on the stripping signal of the compound was also evaluated. The described method was applied to estimate the chlorpyrifos in environmental samples.     

Detection of lead(II) using an glassy carbon electrode modified with Nafion, carbon nanotubes and benzo-18-crown-6

A glassy carbon electrode was modified with Nafion, carbon nanotubes and benzo-18-crown-6 to give an electrode for the selective determination of lead(II) via square wave anodic stripping voltammetry. The use of carbon nanotubes with their extraordinary electrical conductivity and strong adsorption ability warrants high sensitivity. Benzo-18-crown-6 is employed as a “molecular scavenger” because of its excellent selectivity for lead(II). The modified electrode shows enhanced sensitivity, reproducibility and selectivity for lead(II) even without applying an electrical potential during the accumulation time. It responds linearly to lead(II) in the 1 to 30 nM concentration range (with a correlation coefficient of 0.9992) after a 10-min accumulation time. The detection limit is 1 nM. The sensor exhibits excellent selectivity over other heavy metal ions such as Cd(II), Cu(II), Zn(II), and Hg(II).

Electroanalytical detection of zinc in whole blood

Three different electroanalytical techniques for the determination of zinc in blood are investigated. The direct determination in diluted blood via anodic stripping voltammetry at glassy carbon and the use of Nafion-coated glassy carbon mercury electrodes are shown to lack the necessary sensitivity whereas an acoustically assisted double extraction followed by sono-ASV using a glassy carbon electrode is found to be rapid, reliable and sensitive.     

Voltammétrie de l'argent par redissolution anodique sur electrode de carbone vitreux et application au dosage de l'argent dans l'uranium et le pluton

Anodic stripping voltammetry of silver on a glassy carbon electrode, and application to the determination of silver in uranium and plutonium.The use of a glassy carbon electrode for the anodic stripping voltammetry of silver, without deposition of a preliminary mercury film is described. The deposition time, scan rate, rotation speed and molarity of the sulfuric solution have been studied; the method is applied to the determination of silver in uranium and plutonium.     

Cathodic stripping voltammetry of trace Mn(II) at carbon film electrodes

A sensitive voltammetric method is presented for the determination of tract levels of Mn (II) using carbon film electrodes fabricated from carbon resistors of 2 Ω. Determination of manganese was made by square wave cathodic stripping voltammetry (CSV), with deposition of manganese as manganese dioxide. Chronoamperometric experiments were made to study MnO₂ nucleation and growth. As a result, it was found to be necessary to perform electrode conditioning at a more positive potential to initiate MnO₂ nucleation. Under optimised conditions the detection limit obtained was 4 nM and the relative standard deviation for eight measurements of 0.22 nM was 5.3%. Interferences from various metal ions on the response CSV of Mn(II) were investigated, namely Cd(II), Ni(II), Cu(II), Cr(VI), Pb(II), Zn(II) and Fe(II). Application to environmental samples was demonstrated.     

Fabrication of Nano Flower‐shaped Platinum on Glassy Carbon Electrode as a Sensitive Sensor for Lead Electrochemical Analysis

Platinum nanoflowers modified glassy carbon electrodes (PtNFs/GCE) was fabricated simply for lead determination in water samples. The modified electrodes were prepared by electrodeposition in hexachloroplatinic acid solution at constant potential. The influence of deposition time and potential on surface morphology, chemical composition, electrochemical properties of electrode were investigated. At ?0.2 V of potential and 150 s of deposition duration, platinum developed as nanoflower shape and scattered densely all over the glassy carbon surface, producing the largest electrochemically active surface areas. The highest differential pulse stripping voltammetry (DPSV) signal of lead was obtained by using the prepared electrode. Under optimized experimental condition of electrolyte, accumulation potential and time, the peak current was found to be linear proportion to lead concentration in range of 1 to 100 μg L^?1 (slope=0.371) with a limit of detection of 0.398 μg L^?1. The method has good repeatability and reproducibility with relative standard deviations of 1.47 % and 4.83 %, respectively. The modified PtNFs/GCE also demonstrated an excellent long‐term stability with only 9 % decrease in Pb peak current over 30 days. Moreover, the performance of the modified PtNFs/GCE in determination of Pb(II) in two industrial wastewaters was good agreement with data obtained by a graphite furnace atomic absorption spectrometry (GFAAS) method.