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.     

Selective Electrochemical Analysis of Various Metal Ions at an EDTA Bonded Conducting Polymer Modified Electrode

An EDTA‐bonded conducting polymer modified electrode was prepared and characterized by FT‐IR. The modified electrode was used for the selective electrochemical analysis of various trace metal ions such as, Cu(II), Hg(II), Pb(II), Co(II), Ni(II), Fe(II), Cd(II), and Zn(II) at the different pHs by linear sweep and square wave voltammetry. Dynamic ranges were obtained using square wave voltammetry from 0.1 μM to 10.0 μM for Co(II), Ni(II), Cd(II), Fe(II), and Zn(II) and 0.5 nM to 20 nM for Cu(II), Hg(II), and Pb(II) after 10 min of preconcentration. The detection limits were determined to be 0.1 nM, 0.3 nM, 0.4 nM, 50.0 nM, 60.0 nM, 65.0 nM, 80.0 nM, and 90.0 nM for Cu(II), Hg(II), Pb(II), Co(II), Ni(II), Cd(II), Fe(II), and Zn(II), respectively. The technique offers an excellent way for the selective trace determination of various heavy metal ions in a solution.     

Stripping voltammetry study of ultra-trace toxic metal ions on highly selectively adsorptive porous magnesium oxide nanoflowers

We have demonstrated highly selective and sensitive detection of Pb(II) and Cd(II) using a highly selective adsorptive porous magnesium oxide (MgO) nanoflowers. The MgO nanoflower-modified glassy carbon electrode was electrochemically characterized using cyclic voltammetry; and the anodic stripping voltammetric performance of bound Pb(II) and Cd(II) was evaluated using square wave anodic stripping voltammetry (SWASV) analysis. The MgO nanoflower-modified electrode exhibited excellent sensing performance toward Pb(II) and Cd(II) that was never observed previously at bismuth (Bi)-based electrodes. Simultaneous additions of Pb(II) and Cd(II) were investigated in the linear range from 3.3 to 22 nM for Pb(II) and 40 to 140 nM for Cd(II), and detection limits of 2.1 pM and 81 pM were obtained, respectively. Some foreign ions, such as Cu(II), Zn(II) and Cr(III) do not interfere with the detection of Pb(II) and Cd(II). To the best of our knowledge, this is the first example of a highly adsorptive metal oxide with hierarchical micro/nanostructure that allows the detection of both Pb(II) and Cd(II) ions.     

Chemical accumulation and voltammetric determination of traces of nickel(II) at glassy carbon electrodes modified with dimethyl glyoxime containing polymer coatings

The objective of the present study was to develop a solid mercury free electrode for the voltammetric determination of traces of nickel(II) in solution. For this purpose chemically modified electrodes (CME's) were constructed from glassy carbon coated with dimethylglyoxime-containing polymers. CME's based on a composite matrix, which contained polyvinyl chloride, polyaniline, and dimethylglyoxime were shown to possess the ability to accumulate traces of nickel(II) from ammonia buffered aquatic solutions by a purely chemical attachment. Moreover the nickel(II) contents of such solutions could be determined using voltammetric quantitation of the nickel(II) dimethylglyoximate deposits on the CME surfaces and the standard addition technique. The CME surfaces could subsequently be regenerated by acid treatment. The limit of detection for Ni(II) following a 240 s chemical deposition was estimated as 18 mug Ni l(-1), and the CME results for traces of Ni(II) in fresh water compared well with the results obtained by atomic absorption spectroscopy. Moreover the CME's retained their sensitivity for more than two days, i.e. significantly longer than the 3 h, during which analogous carbon paste electrodes completely lost their affinity to nickel(II).     

Accumulation and voltammetric determination of cobalt at zeolite-modified electrodes

Chemically modified electrodes based on zeolite-containing graphite pastes were constructed and evaluated as sensor electrodes for the voltammetric determination of trace cobalt in solution. Zeolite molecular sieves with pore sizes of 3, 4, and 5 Å were all suitable for chemical deposition and subsequent voltammetric quantitation of trace Co(II). In order to cover a large range of parameters, the investigations were carried out using three zeolites (A, X, and Y), selected for their different cation-exchange capacities and ion-sieving properties. The analytical scheme, “preconcentration/voltammetric detection” for the determination of cobalt(II) species using zeolite-modified carbon paste electrodes (ZMCPE) was chosen. Compared to the corresponding unmodified electrodes, improvements in sensitivity were observed when using ZMCPEs due to analyte accumulation at the electrode’s surface by ion exchange in zeolite particles. The detection limit obtained for Co(II) was 3 ppm following 15 min of chemical deposition. A good correlation was found between the results obtained by ion exchange voltammetry and conventional ion-exchange characterization.     

Mechanism for the atomic layer deposition of copper using diethylzinc as the reducing agent: a density functional theory study using gas-phase molecules as a model

We present theoretical studies based on first-principles density functional theory calculations for the possible gas-phase mechanism of the atomic layer deposition (ALD) of copper by transmetalation from common precursors such as Cu(acac)(2), Cu(hfac)(2), Cu(PyrIm(R))(2) with R = (i)Pr and Et, Cu(dmap)(2), and CuCl(2) where diethylzinc acts as the reducing agent. An effect on the geometry and reactivity of the precursors due to differences in electronegativity, steric hindrance, and conjugation present in the ligands was observed. Three reaction types, namely, disproportionation, ligand exchange, and reductive elimination, were considered that together comprise the mechanism for the formation of copper in its metallic state starting from the precursors. A parallel pathway for the formation of zinc in its metallic form was also considered. The model Cu(I) molecule Cu(2)L(2) was studied, as Cu(I) intermediates at the surface play an important role in copper deposition. Through our study, we found that accumulation of an LZnEt intermediate results in zinc contamination by the formation of either Zn(2)L(2) or metallic zinc. Ligand exchange between Cu(II) and Zn(II) should proceed through a Cu(I) intermediate, as otherwise, it would lead to a stable copper molecule rather than copper metal. Volatile ZnL(2) favors the ALD reaction, as it carries the reaction forward.     

Subtractive differential pulse anodic stripping voltammetry at a stationary mercury-coated glassy carbon electrode

The application of subtractive mode differential pulse anodic stripping voltammetry (SDPASV) at a stationary mercury-coated glassy carbon electrode for the analysis of labile Zn(II), Cd(II), Pb(II) and Cu(II) is described. It is shown that the method has an improved sensitivity to Cu(II) owing to elimination of high background currents normally encountered in normal mode DPASV at the TFME. The sensitivity limits of the present method to Cd(II) and Cu(II) is estimated to be 0.025 and 0.067 ppb respectively, when a 2 min deposition time is used. It is suggested that the high sensitivity of the method coupled to the relative simplicity of the stationary electrodes could make the method useful in environmental and natural water studies.     

Electrochemical approach to monitoring metal exchange reaction of acetylacetonate complexes with cadmium, copper and zinc ions

Metal exchange reactions of acetylacetonate complexes with Cd(II), Cu(II) and Zn(II) ions were investigated by using cadmium and copper ion selective electrodes. Changes in the electrode potential and pH of the solutions were monitored upon adding the pertinent metal Zn(II) of the acetylacetonate (AA) complexes. In the reverse system in which a stable Cu-AA complex exists in the solution prior to adding a secondary metal ion (Cd(II) or Zn(II)), no Cu(II) was replaced by either ion. In the systems containing Cd(II) and Zn(II) as a complexed form with AA or as free ions, the exchange reactions were not explained by considering the equilibrium stability constants of the Cd-AA and Zn-AA complexes.     

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.     

Cathodic stripping voltammetry of nickel: sonoelectrochemical exploitation of the Ni(III)/Ni(II) couple

The exploitation of the Ni(III)/Ni(II) transition as a means of quantifying the concentration of nickel within industrial samples was assessed. The methodology relies upon the reagentless electrodeposition of Ni onto a glassy carbon electrode and the subsequent oxidative conversion of the metallic layer to Ni(III). The analytical signal is derived from a cathodic stripping protocol in which the reduction of the Ni(III) layer to Ni(II) is monitored through the use of square wave voltammetry. The procedure was refined through the introduction of an ultrasonic source which served to both enhance the deposition of nickel and to remove the nickel hydroxide layer that results from the measurement process. A well-defined stripping peak was observed at +0.7 V (vs. AgAgCl) with the response found to be linear over the range 50 nM to 1 μM (based on a 30 s deposition time). Other metal ions such as Cu(II), Mn(II), Cr(III), Pb(II), Cd(II), Zn(II), Fe(III) and Co(II) did not interfere with the response when present in hundred fold excess. The viability of the technique was evaluated through the determination of nickel within a commercial copper nickel alloy and validated through an independent comparison with a standard ICP-AES protocol.     

AgNP/Bi/Nafion‐modified Disposable Electrodes for Sensitive Zn(II), Cd(II), and Pb(II) Detection in Aerosol Samples

A new method for modifying electrodes with Ag nanoparticles (AgNPs) using electrospray deposition for sensitive, selective detection of Zn(II), Cd(II), and Pb(II) in aerosol samples when combined with Bismuth and Nafion coating and square‐wave anodic stripping voltammetry (SWASV) is reported. Carbon stencil‐printed electrodes (CSPEs) fabricated on a polyethylene transparency (PET) sheet were produced for an inexpensive, simple to fabricate, disposable sensor that can be used with the microliter sample volumes for analysis. Sensor performance was improved by modifying the electrode surface with electrospray‐deposited AgNPs. The use of electrospray deposition resulted in more uniform particle dispersion across the electrode surface when compared to drop‐casting. Using AgNP‐modified electrodes combined with Bi and Nafion, experimental detection limits (LODs) of 5.0, 0.5, and 0.1 μg L⁻¹ for Zn(II), Cd(II), and Pb(II), respectively, were achieved. The linear working ranges were 5.0–400.0 μg L⁻¹, 0.5–400.0 μg L⁻¹, and 0.1–500.0 μg L⁻¹ for Zn(II), Cd(II), and Pb(II), respectively. Interference studies showed Cu(II) was the only metal that interfered with this assay but inference could be eliminated with the addition of ferricyanide directly to the sample solution. This electrochemical sensor was applied for the simultaneous determination of Zn(II), Cd(II), and Pb(II) within source particulate matter (PM) samples collected on filters using an aerosol test chamber.     

Electrodeposition of zinc + cobalt alloys.: Relation between the electrochemical response and the composition and morphology of the deposits

The electrodeposition of cobalt and zinc + cobalt alloy in aqueous chloride solution has been studied on vitreous carbon electrodes under different concentration conditions (total concentration of metallic ion 0.1 mol dm ⁻³, chloride ion 1 mol dm ⁻³, pH = 3), particularly during the initial stages of the deposition process. For the alloy a relation has been found between the shape of the current-time transients, the morphology of the deposits, the stripping analysis and the results of X-ray microanalysis. The different alloy phases present in the deposits were identified using X-ray microanalysis data, stripping voltammetry results and literature data.The results indicate that the electrocrystallization of cobalt is inhibited even at very low concentrations of zinc in solution: voltammetric and galvanostatic results indicate that the deposition potentials always correspond to more negative values than those for cobalt deposition. This inhibition depends strongly on both the metallic ion ratio in solution and the applied overpotential (or current density). For Zn(II)/Co(II) ratios greater than 1/9, low overpotentials (or low current densities) favoured homogeneous and compact deposits that were rich in zinc and were mainly composed of γ-phases of zinc + cobalt alloy. However, when high overpotentials or current densities were used and/or when the Zn(II)/Co(II) ratio was very low (< 1/9), dendritic and non-homogeneous cobalt-rich deposits were obtained.     

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.     

Sequential injection anodic stripping voltammetry with monosegmented flow and in-line UV digestion for determination of Zn(II), Cd(II), Pb(II) and Cu(II) in water samples

A cost-effective sequential injection system incorporating with an in-line UV digestion for breakdown of organic matter prior to voltammetric determination of Zn(II), Cd(II), Pb(II) and Cu(II) by anodic stripping voltammetry (ASV) on a hanging mercury drop electrode (HMDE) of a small scale voltammetric cell was developed. A low-cost small scale voltammetric cell was fabricated from disposable pipet tip and microcentrifuge tube with volume of about 3 mL for conveniently incorporated with the SI system. A home-made UV digestion unit was fabricated employing a small size and low wattage UV lamps and flow reactor made from PTFE tubing coiled around the UV lamp. An in-line single standard calibration or a standard addition procedure was developed employing a monosegmented flow technique. Performance of the proposed system was tested for in-line digestion of model water samples containing metal ions and some organic ligands such as strong organic ligand (EDTA) or intermediate organic ligand (humic acid). The wet acid digestion method (USEPA 3010a) was used as a standard digestion method for comparison. Under the optimum conditions, with deposition time of 180 s, linear calibration graphs in range of 10-300 μg L⁻¹ Zn(II), 5-200 μg L⁻¹ Cd(II), 10-200 μg L⁻¹ Pb(II), 20-400 μg L⁻¹ Cu(II) were obtained with detection limit of 3.6, 0.1, 0.7 and 4.3 μg L⁻¹, respectively. Relative standard deviation were 4.2, 2.6, 3.1 and 4.7% for seven replicate analyses of 27 μg L⁻¹ Zn(II), 13 μg L⁻¹ Cd(II), 13 μg L⁻¹ Pb(II) and 27 μg L⁻¹ Cu(II), respectively. The system was validated by certified reference material of trace metals in natural water (SRM 1640 NIST). The developed system was successfully applied for speciation of Cd(II) Pb(II) and Cu(II) in ground water samples collected from nearby zinc mining area.     

A new chelating resin for preconcentration and determination of Mn(II), Ni(II), Cu(II), Zn(II), Cd(II), and Pb(II) by flame atomic absorption spectrometry

A new polychelatogen, AXAD-16-1,2-diphenylethanolamine, was developed by chemically modifying Amberlite XAD-16 with 1,2-diphenylethanolamine to produce an effective metal-chelating functionality for the preconcentration of Mn(II), Ni(II), Cu(II), Zn(II), Cd(II), and Pb(II) and their determination by flame atomic absorption spectrometry. Various physiochemical parameters that influence the quantitative preconcentration and recovery of metal were optimized by both static and dynamic techniques. The resin showed superior extraction efficiency with high-metal loading capacity values of 0.73, 0.80, 0.77, 0.87, 0.74, and 0.81 mmol/g for Mn(II), Ni(II), Cu(II), Zn(II), Cd(II), and Pb(II), respectively. The system also showed rapid metal-ion extraction and stripping, with complete saturation in the sorbent phase within 15 min for all the metal ions. The optimum condition for effective metal-ion extraction was found to be a neutral pH, which is a great advantage in the preconcentration of trace metal ions from natural water samples without any chemical pretreatment of the sample. The resin also demonstrated exclusive ion selectivity toward targeted metal ions by showing greater resistivity to various complexing species and more common metal ions during analyte concentration, which ultimately led to high preconcentration factors of 700 for Cu(II); 600 for Mn(II), Ni(II), and Zn(II); and 500 for Cd(II) and Pb(II), arising from a larger sample breakthrough volume. The lower limits of metal-ion detection were 7 ng/mL for Mn(II) and Ni(II); 5 ng/mL for Cu(II), Zn(II), and Cd(II), and 10 ng/mL for Pb(II). The developed resin was successful in preconcentrating metal ions from synthetic and real water samples, multivitamin-multimineral tablets, and curry leaves (Murraya koenigii) with relative standard deviations of < or = 3.0% for all analytical measurements, which demonstrated its practical utility.     

On the mechanism of electroreduction of sulphur-containing ligands induced by the electroreduction of transition metal cations

The large scale electrolysis of Zn(II), Cd(II), Hg(II), Cu(II), Ni(II), Co(II), Co(III), Fe(II), Mn(II), Cr(II), Cr(III), Bi(III), In(III) and Sb(III) at mercury electrodes in presence of mercaptoacetic acid, 3-mercaptopropionic acid, cysteine and thiourea was carried out and the products were investigated. In case of transition metal ions the catalytic reduction of organic compounds resulting in the formation of sulphide ions was found. There are two possible ways of the production of these ions: (i) consisting in the formation of a complex between transition metal ion and organic ligand which is subsequently, reduced, and (ii) direct electroreduction of organic compound on the electrode modifiied by the deposition of metal and metal sulphide. For both cases the mechanism of electroreduction was discussed.     

Gas sensitivity of etioporphyrin metal complexes in thin films

It is shown that porphyrin metal complexes have the potential for the creation of various gas sensors; the gas sensing properties of the materials on their basis change upon the replacement of the central metal atom and substituents in the porphyrin core. Films of etioporphyrin-II were prepared by vacuum deposition onto a front shaft system of electrodes on a pyroceramic support. Calibration dependences of the analytical signal (conductivity) on the concentration of ammonia were obtained. It was found that UV irradiation on the sensor layer enhances the sensitivity of ammonia determination. Relative sensitivities of thin films based on Co(II), Ni(II), Cu(II), Zn(II), Pd(II) and Pt(II) etioporphyrin complexes in the temperature range from 303 K to 423 K and ammonia concentrations from 1.5 to 75 mg/m³ were determined. The relative sensitivity attains a maximum (0.8) at an ammonia concentration of 7.5 mg/m³ for the Co(II) etioporphyrin at 333 K in a dark mode, or at 303 K and under UV irradiation (λ = 406 nm, P = 1 mW). An experimental setup was assembled that allowed measurements at the controlled temperature and humidity of the gas and its mixtures with inert gases or air. The conditions of ammonia detection were optimized.     

Antimony Film Electrode Prepared In Situ in Hydrogen Potassium Tartrate in Anodic Stripping Voltammetric Trace Detection of Cd(II), Pb(II), Zn(II), Tl(I), In(III) and Cu(II)

An antimony film electrode (SbFE) was prepared in situ on a glassy carbon support and in a new supporting electrolyte, a saturated solution of hydrogen potassium tartrate in which Sb(III) ions were complexed using tartrate. Its performance in anodic stripping voltammetric (ASV) determination of Cd(II), Pb(II), Zn(II), Tl(I), In(III) and Cu(II) traces was examined. It was found that 1.2 mg/L of Sb(III) yields the finest quality SbFE for analytical purposes. The procedure with in situ SbFE ensures well‐defined anodic stripping voltammetric curves of the investigated elements, low detection limits (0.5–3.8 µg/L), good reproducibility (1–5 %) and satisfactory sensitivity (32–184 nA/(µg/L)).     

Developing On-Site Trace Level Speciation of Lead,Cadmium and Zinc by Stripping Chronopotentiometry (SCP): Fast Screening and Quantification of Total Metal Concentrations

Electrochemical stripping techniques are interesting candidates for carrying out onsite speciation of environmentally relevant trace metals due to the existing low-cost portable instrumentation available and the low detection limits that can be achieved. In this work, we describe the initial analytical technique method development by quantifying the total metal concentrations using Stripping Chronopotentiometry (SCP). Carbon paste screen-printed electrodes were modified with thin films of mercury and used to quantify sub-nanomolar concentrations of lead and cadmium and sub-micromolar concentrations of zinc in river water. Low detection limits of 0.06 nM for Pb(II) and 0.04 nM for Cd(II) were obtained by the standard addition method using a SCP deposition time of 180 s. The SCP results obtained for Pb(II) and Cd(II) agreed with those of inductively coupled plasma mass spectrometry (ICP-MS). The coupling of SCP with screen-printed electrodes opens up excellent potential for the development of onsite speciation of trace metals. Due to the low analysis throughput obtained for the standard addition method, we also propose a new, more rapid screening Cd(II) internal standard methodology to significantly increase the number of samples that can be analyzed per day.     

Spectrophotometric determination of traces of metallic ions and their mixtures with 3-methyl-1,2-cyclopentanodione dithiosemicarbazone: I. Zinc,cadmium, and mercury

The properties of zinc, cadmium, and mercury complexes of 3-methyl-1,2-cyclopentanodione dithiosemicarbazone and the optimal conditions for their formation are described. The complexes were used with success in the photometric determination of traces of zinc, cadmium, and mercury. Seven procedures are proposed for the accurate analysis of Zn(II)-Cd(II), Zn(II)-Hg(II), Zn(II)-Bi(III), Cd(II)-Hg(II), Cd(II)-Bi(III), Hg(II)-Bi(III), and Zn(II)-Cd(II)-Hg(II) mixtures. Satisfactory results were obtained.