Determination of trace amounts of nickel by differential pulse adsorptive cathodic stripping voltammetry using calconcarboxylic acid as a chelating agent

A method for the determination of nickel(II) by stripping voltammetry is described. The method is based on the adsorptive accumulation of nickel(II) calconcarboxylic acid complex onto a hanging mercury drop electrode (HMDE), followed by the reduction of the adsorbed complex using differential pulse voltammetry. The optimum operating conditions and parameters were found to be 0.05 M NH₃/NH₄Cl buffer (pH = 9.5) as the supporting electrolyte, a ligand concentration of 1 × 10^?6 M, accumulation potential of ?0.5 V (vs. Ag/AgCl) and accumulation time of 60 s. At the optimized conditions, the peak current is proportional to the concentration of nickel in the range of 1.7 × 10^?9 to 4.7 × 10^?7 M (0.1–28 ng ml^?1) with a detection limit of 0.05 ng ml^?1. The relative standard deviation (n = 10) at nickel concentrations of 2, 10 and 15 ng ml^?1 varies in the range 0.76 to 2.1%. Possible interferences by metal ions, which are of great significance in real matrices, have been studied. The method was successfully applied to the determination of nickel content in a chocolate sample.     

Voltammetric and flow-injection determination of carbohydrates using composite electrodes based on carbon nanotubes and Nickel(II) hexacyanoferrate

The catalytic activities of oxo and hydroxo forms of nickel(II) on the surface of a nickel deposit and an inorganic film of nickel(II) hexacyanoferrate(III) (NiHCF) electrodeposited on a glassy-carbon electrode both unmodified and modified by multi-wall or single-wall (also functionalized) carbon nanotubes in the electrooxidation of glucose, sucrose, and maltose are compared. A more pronounced catalytic effect was obtained in the electrooxidation of these carbohydrates on an electrode modified with functionalized singlewall carbon nanotubes and a NiHCF film. Methods are proposed for the voltammetric and flow-injection determination of carbohydrates on this composite electrode. A linear dependence of the analytical signal on the analyte concentration was observed in the range from 5 × 10^?7 to 5 × 10^?2 M under stationary conditions and from 0.003 to 0.3 μmol under flow conditions.     

Catalytic Adsorptive Stripping Chronopotentiometry of Co(II)‐DMG‐Bromate System at an In Situ Plated Lead Film Electrode

A novel catalytic adsorptive stripping chronopotentiometric (CC‐CAdSCP) procedure for the determination of Co(II) traces was developed using a lead film electrode (PbFE). The PbFE was generated in situ on a glassy carbon support from a 0.1 M ammonia buffer containing 1×10^?5 M Pb(II), 6.5×10^?5 M DMG and the target metals. An addition of 0.2 M NaBrO₃ to the solution yielded an 11‐fold catalytic enhancement of chronopotentiometric response of the Co(II)‐DMG complex. The CC‐CAdSCP curves were well‐developed, sharp and reproducible (RSD 5.0 % for 5×10^?9 M Co(II)). The limit of detection for Co(II) for 210 s of accumulation time was 4×10^?10 M (0.024 µg L^?1). In addition, the elaborated method allowed the simultaneous quantification of Co(II) and Ni(II) simultaneously.     

Determination of trace amounts of nitrite by single-sweep polarography

A single-sweep polarographic determination of nitrite in 0.2 M sulphuric acid medium containing nickel(II) sulphate and ammonium thiocyanate is described. The ternary complex (NiSCNNO)⁺ which is formed in the solution is strongly adsorbed on the surface of the mercury electrode and an adsorptive polarographic wave at ?0.57 V (vs. SCE) is related to the concentration of nitrite in the range 2.0 × 10^?8-1.0 × 10^?6 M. The detection limit is 8 × 10^?9 M. The relative standard deviation is 1.5% and the regression coefficient is 0.998. Most common anions and cations do not interfere. The mechanism of the electrode process was studied by several electrochemical methods. The polarographic wave is attributed to the reduction of nitrogen monoxide in the adsorbed (NiSCNNO)⁺ complex to hydroxylamine. The procedure was applied to the determination of trace amounts of nitrite in sausage, water and nitrate.     

Determination of trace thiocyanate by linear sweep polarography

In a thiocyanate solution containing iron (II), nitrite and ascorbic acid, a linear-sweep polarographic wave appears at ?0.42 V (vs. SCE). In anodic sweeps, the derivative peak current is directly proportional to the concentration of thiocyanate over the range 2×10^?8?1×10^?6 M; the detection limit is 1×10^?8 M. The procedure is used for the determination of trace thiocyanate (10^?3?10^?4 M) in saliva. The mechanism of the electrode process is discussed; the polarographic wave is ascribed to catalytic reduction of dissolved oxygen in the presence of an adsorbed ternary Fe/SCN/NO complex.     

Electrocatalytic oxidation of methanol by ZSM-5 nanozeolite-modified carbon paste electrode in alkaline medium

Development of a novel modified electrode for electrocatalytic oxidation of methanol in order to decrease overvoltage is importance. In this paper, carbon paste electrode (CPE) was modified by ZSM-5 nanozeolite. The average diameter of used nanozeolite was 97 nm. Ni²⁺ ions were incorporated to the nanozeolite by immersion of the modified electrode in a 0.1 M nickel chloride solution. Then, electrochemical studies of this electrode were performed by using cyclic voltammetry(CV) in alkaline medium. This modified electrode was used as an anode for the electrocatalytic oxidation of methanol in 0.1 M of NaOH solution. The obtained data demonstrated that ZSM-5 nanozeolite at the surface of CPE improves catalytic efficiency of the dispersed nickel ions toward methanol oxidation. The values of electron transfer coefficient, charge-transfer rate constant, and the electrode surface coverage are obtained 0.61, 0.2342 s^?1, and 4.33 × 10^?8 mol cm^?2, respectively. Also, the mean value of catalytic rate constant between the methanol and redox sites of electrode and diffusion coefficient were found to be 2.54 × 10⁴ cm³ mol^?1 s^?1 and 1.85 × 10^?8 cm² s^?1, respectively. Obtained results from both CV and chronoamperometric techniques indicated that the electrode reaction is a diffusion-controlled process.     

Cyanide ion selective solid contact electrode based on nickel complex of N,N′-bis-(4-phenylazosalicylidene)-o-phenylene diamine ionophore

A cyanide ion selective poly(aniline) solid contact electrode based on nickel complex of N,N′-bis-(4-phenylazosalicylidene)-o-phenylenediamine ionophore was successfully developed. The electrode exhibits a good linear response of 58.7 mV/decade (at 20 ± 0.2°C, r ² = 0.998) with in the concentration range of 1 × 10^?1.0-1 × 10^?6.0 M cyanide. The composition of this electrode was: ionophore 0.300, polyvinylchloride 0.300, 2-nitrophenyloctyl ether 0.670 (mass). This 2-nitrophenyloctyl ether plasticizer provides the best response characteristics. The electrode shows good selectivity for cyanide ion in comparison with any other anions and is suitable for use with aqueous solutions of pH 4.6–6.3. The standard deviations of the measured emf difference were ±1.92 and ±1.87 mV for cyanide sample solutions of 1.0 × 10^?2 M and 1.0 × 10^?3 M, respectively. The stabilization time was less than 183 s and response time was less than 38 s.     

Adsorptive stripping voltammetry of nickel at a bare glassy carbon electrode

A bare glassy carbon electrode is applied to nickel determination by adsorptive stripping voltammetry in the presence of dimethylglyoxime as a complexing agent. A procedure of nickel determination and electrode regeneration was proposed. The calibration graph for Ni(II) for an accumulation time of 120?s was linear from 2?×?10^?9 to 1?×?10^?7?mol?L^?1. The detection limit was 8.2?×?10^?10?mol?L^?1. The relative standard deviation for a solution containing 2?×?10^?8?mol?L^?1 of Ni(II) was 4.1%. The proposed procedure was applied for Ni(II) determination in certified water reference materials.     

Doubly Modified Electrodes for the Selective Determination of Dopamine in the Presence of Interfering Species

In this paper, we describe the double modification of the glassy carbon electrode surface with two polymer layers for the selective determination of dopamine. The first layer was the electropolymerized macrocyclic nickel complex acting as an electrocatalyst for the dopamine oxidation and the second layer the polyurethane benzyl L ‐glutamate (PUBLG) for screening interfering species. Hydrolyzed PUBLG (PU‐C) showed a better screening effect. Thus prepared GC/Ni(II) complex film/PU‐C electrodes exhibited improved selectivity and better performance than unmodified counterparts, with minimum passivation even in the presence of large excess of interferents. Under optimal conditions, these electrodes showed a linear response over a dopamine concentration range of 2.5×10^?7 and 3.0×10^?5 M with a correlation coefficient of 0.999 and detection limit (at S/N=3) of 8.0×10^?8 M. The recoveries of dopamine in the 5‐fold diluted human urine sample were 96.9% for 4 measurements. The rate constant for the dopamine oxidation measured by the rotating disk electrode was found to be 1.1×10^?3 cm s^?1.     

Thiocyanate-Selective PVC Membrane Electrode Based on Copper and Nickel Complexes of Para-tolualdehydesemicarbazone as Carrier

Abstract

Copper(Cu) and nickel(Ni) complexes of para-tolualdehydesemicarbazone (pTSC) were used as carrier for an thiocyanate ion–selective electrode. The Ni(II)pTSC demonstrated higher selectivity for thiocyanate ions with better performance than Cu(II)pTSC as carrier. The electrode shows a Nernstian slope of 58.8 ± 0.3 mV decade^?1 with improved linear range of 1 × 10^?2 to 1 × 10^?7 M and a low detection limit of 1.25 × 10^?7 M in the pH range of 3–10, giving a relatively fast response and reversibility within 10 s. The selectivity coefficient was calculated using matched potential method. The electrode worked well for nearly 3 months. The response mechanism is discussed by UV-visible spectroscopic technique. The electrodes were used in potentiometric titration of thiocyanate with silver nitrate. Further, the electrode was successfully applied to determine the thiocyanate content in physiological fluids.     

Electrocatalytic oxidation of formaldehyde and methanol on Ni(OH)2/Ni electrode

A nickel hydroxide-modified nickel electrode (Ni(OH)₂/Ni) was successfully prepared by the cyclic voltammetry (CV) method and the electrocatalytic properties of the electrode for formaldehyde and methanol oxidation have been investigated respectively. The Ni(OH)₂/Ni electrode exhibits high electrocatalytic activity in the reaction. A new method has been developed for formaldehyde determination at the nickel hydroxide-modified nickel electrode and the experimental parameters were optimized. The oxidation peak current is linearly proportional to the concentration of formaldehyde in the range of 7.0 × 10^?5 to 1.6 × 10^?2 M with a detection limit of 2.0 × 10^?5 M. Recoveries of artificial samples are between 93.3 and 103.5%. The effect of scan rate and methanol concentration on the electrochemical behavior of methanol were investigated respectively.     

Carbon Paste Electrode Plated with Lead Film. Voltammetric Characteristics and Application in Adsorptive Stripping Voltammetry

A lead film plated in situ at a carbon paste support was tested as a novel, potential electrode for adsorptive stripping voltammetric determination of cobalt traces in an ammonia buffer solution. To show the practical applicability of the new electrode, a catalytic adsorptive Co system in a supporting electrolyte containing 0.1 M ammonia buffer, 5×10^?4 M nioxime and 0.25 M nitrite was selected and investigated as a model solution. Pb and Co ions were simultaneously accumulated in situ on the electrode surface: Pb ions electrochemically at ?1.3 V) and then at ?0.75 V, at which potential the Co(II)‐nioximate complex was also pre‐concentrated via adsorption. Instrumental parameters, such as the time of nucleation and formation of Pb film deposits, the time of accumulation of the Co‐nioxime complex at the PbF/CPE, and the procedures of electrode regeneration, were optimized to obtain good reproducibility and sensitivity of the Co response. The optimized procedure yields favorable and highly stable stripping responses with good precision (RSD=3% for a 5×10^?8 M Co) and good linearity (up to 5×10^?7 M, coefficient of determination, R=0.996). The detection limit was 4×10^?10 M Co (0.023 μg L^?1) for an accumulation time of 120 s. The method enables the determination of Co in the presence of high excesses of Ni or Zn. The voltammetric data were correlated with the structural characterization by scanning electron microscopy (SEM) and X‐ray fluorescence spectroscopy (XRF).     

Acetylferrocene Modified Carbon Paste Electrode; A Sensor for Electrocatalytic Determination of Hydrazine

The electrocatalytic oxidation of hydrazine at a carbon paste electrode spiked with acetylferrocene as a mediator was studied by cyclic voltammetry, differential pulse voltammetry, and chronoamperometry. In contrast to other ferrocenic compounds, acetylferrocene exhibits a chemical irreversible behavior, but it can act as an effective mediator for electrocatalytic oxidation of hydrazine, too. The heterogeneous electron transfer rate constant between acetylferrocene and the electrode substrate (carbon paste) and the diffusion coefficient of spiked acetylferrocene in silicon oil were estimated to be about 3.45×10^?4 cm s^?1 and 4.45×10^?9 cm² s^?1, respectively. It has been found that under the optimum conditions (pH 7.5) the oxidation of hydrazine occurs at a potential of about 228 mV less positive than that of an unmodified carbon paste electrode. The catalytic oxidation peak current of hydrazine was linearly dependent on its concentration and the obtained linear range was 3.09×10^?5 M–1.03×10^?3 M. The detection limit (2σ) has been determined as 2.7×10^?5 M by cyclic voltammetry. Also, the peak current was increased linearly with the concentration of hydrazine in the range of 1×10^?5 M–1×10^?3 M by differential pulse voltammetry with a detection limit of 1×10^?5 M. This catalytic oxidation of hydrazine has been applied as a selective, simple, and precise new method for the determination of hydrazine in water samples.     

Catalytic Adsorptive Stripping Voltammetry of Cobalt in the Presence of Dimethylglyoxime and Nitrite at In Situ Plated Lead–Copper Film Electrode

A lead‐copper film electrode was proposed for Co(II) determination by catalytic adsorptive stripping voltammetry. The electrode was plated in situ and hence the exchange of a solution after plating step was not required. At optimized conditions the calibration graph for Co(II) was linear from 5×10^?10 to 2×10^?8 mol L^?1 for accumulation time of 15 s. The relative standard deviation for Co(II) determination at concentration 5×10^?9 mol L^?1 was 4.1%. The detection limits for Co(II) were 1.2×10^?10 and 1.0×10^?11 mol L^?1 for an accumulation time of 15 and 180 s, respectively. The method was applied to Co(II) determination in certified reference material and other water samples.     

Investigation of Electrochemical Oxidation of Methanol at a Carbon Paste Electrode Modified with Ni(II)‐BS Complex and Reduced Graphene Oxide Nano Sheets

In the present research, the electro oxidation of methanol was investigated by different electrochemical methods at a carbon paste electrode (CPE) modified with bis(salicylaldehyde)‐nickel(II)‐dihydrate complex (Ni(II)‐BS) and reduced graphene oxide (RGO) (which named Ni(II)‐BS/RGO/CPE) in an alkaline solution. This modified electrode showed very efficient activity for oxidation of methanol. It was found that methanol was oxidized by NiOOH groups generated by further electrochemical oxidation of nickel (II) hydroxide on the surface of the modified electrode. The rate constant and electron transfer coefficient were calculated to be 2.18 s^?1 and 0.4, respectively. The anodic peak currents revealed a linear dependency with the square root of scan rate. This behaviour is the characteristic of a diffusion controlled process, so the diffusion coefficient of methanol was found to be 1.16×10^?5 cm² s^?1 and the number of transferred electron was calculated to be 1. Moreover, differential pulse voltammetry (DPV) investigations showed that the peak current values were proportional to the concentration of methanol in two linear ranges. The obtained linear ranges were from 0.5 to 100.0 µM (R²=0.991) and 400.0 to 1300.0 µM (R²=0.992), and the detection limit was found to be 0.19 µM for methanol determination. Generally, the Ni(II)‐BS/RGO/CPE sensor was used for determination of methanol in an industrial ethanol solution containing 4.0 % methanol.     

Synthesis,characterization and electrochemical behavior of a new diimine-dioxime compound and its application in developing Hg(II)-selective membrane electrode

In this work, a new diimine-dioxime compound (N,N′-bis[1-biphenyl-2-hydroxyimino-2-(4-chloroanilino)-1-ethylidene]-1,4-phenylenediamine) was synthesized and characterized by a combination of elemental analyses, FT-IR, ¹H- and ¹³C-NMR spectra. The extraction ability of the new compound has been examined in chloroform by using several transition metal picrates such as Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Pb(II), Cd(II) and Hg(II). It has been observed that diimine-dioxime compound shows a high affinity to Hg(II) ion. The electrochemical measurements of the compound were performed by cyclic voltammetry in acetonitrile solution at room temperature, and two irreversible oxidation waves were observed. A Hg(II)-selective electrode based on the diimine-dioxime compound has been developed. The electrode showed linear responses with Nernstian slopes of 33 ± 1 mV per decade over a wide concentration range (1.0 × 10^?2–8.0 × 10^?6 M). The limit of detection was 2.4 × 10^?6 M. The electrode has a response time about 10–15 s and it did not show a considerable divergence in its potential response over a period of 1 month. The proposed electrode revealed selectivity towards Hg(II) ion in the presence of various cations. The electrode could be used over a wide pH range of 4.0–9.0. The electrode can be successfully used as an indicator electrode for potentiometric titration of Hg(II) with EDTA.     

Simultaneous voltammetric determination of dopamine and ascorbic acid at an electrode modified with the gold-palladium binary system

The catalytic activities of gold, palladium, and rhodium particles and their binary systems electrodeposited on the surface of a glassy-carbon electrode in the oxidation of dopamine and ascorbic acid are compared. As compared to individual noble metals, the Au-Pd binary system exhibits a higher catalytic activity that manifests itself in a multiple increase in the oxidation current of the mediator and in a decrease in the oxidation potential of the substrate. It is found that dopamine and ascorbic acid can be simultaneously determined by voltammetry at an electrode modified with the Au-Pd binary system. The catalytic currents of substrate oxidation are linear functions of the concentrations in the ranges from (1 × 10^?3 to 1 × 10^?7) M for dopamine and from (5 × 10^?3 to 1 × 10^?6) M for ascorbic acid.     

Electrocatalytic Oxidation of Sulfite on a Nickel Aquapentacyanoferrate Modified Electrode: Application for Simple and Selective Determination

An electroactive metal cyanometallate complex, nickel aquapentacyanoferrate (NAPCF) was synthesized and characterized using XRD and UV‐vis spectral studies. The solid complex was then mechanically immobilized on the surface of a paraffin impregnated graphite electrode (PIGE) and the NAPCF modified electrode was characterized using cyclic voltammetry. The dependence of the modified electrode was tested in terms of supporting electrolyte, scan rate and pH of the medium. The electrocatalytic oxidation of sulfite at the modified electrode was investigated by cyclic voltammetry, hydrodynamic voltammetry and chronoamperometry techniques. It was found that the NAPCF modified electrode efficiently exhibited electrocatalytic activity for the oxidation of sulfite with relatively high sensitivity, selectivity and long life of activity. Based on the electrocatalytic oxidation, the NAPCF modified electrode was used as a sensor for the determination of sulfite. The linear working range for the determination of sulfite was 2.78×10^?6 M to 3.00×10^?3 M with a detection limit of 9.26×10^?7 M. The electrode was applied for the determination of sulfite in real samples satisfactorily.     

Determination of lead (II) ion by highly selective and sensitive lead (II) membrane electrode based on 2-(((E)-2-((E)-1-(2-hydroxyphenyl) methyliden)hydrazono)metyl)phenol

A PVC (poly vinyl chloride) membrane electrode for lead ion based on 2-(((E)-2-((E)-1-(2-hydroxyphenyl)methyliden)hydrazono)metyl)phenol (HMHMP) as a membrane carrier was prepared. This electrode exhibited linear response with Nernstian slope of 29.2?±?0.2?mV per decade within the concentration range of 2.0?×?10^?7–1.0?×?10^?1?M lead ion. The limit of detection, as determined from the intersection of the extrapolated linear segments of the calibration plot, was 8.0?×?10^?8 M. The electrode exhibited high selectivity for Pb (II). The response time of the electrode was about 5–10?s for different concentrations. The electrode is suitable for use in aqueous solutions in a pH range of 5.0–7.5. It was used as an indicator electrode in a titration of Pb (II) with chromate at constant pH. This electrode was used for the determination of lead in ore samples, and the results were in agreement with those obtained with an atomic absorption spectroscopy (AAS) method. Also lead selective electrode was used for monitoring of lead in spiked samples of the Zayanderud River and waste water by the potentiometry technique.     

Polymeric membrane and coated graphite electrode based on newly synthesized tetraazamacrocyclic ligand for trace level determination of nickel ion in fruit juices and wine samples

Novel polymeric membrane electrode (PME) and coated graphite electrode (CGE) for nickel ion were prepared based on 2,9-(2-methoxyaniline)₂-4,11-Me₂-[14]-1,4,8,11-tetraene-1,5,8,12-N₄ as a suitable neutral ionophore. The addition of lipophilic anion excluder (NaTPB) and various plasticizers viz o-nitrophenyloctylether (o-NPOE), dioctylphthalate (DOP), dibutylphthalate (DBP), 1-chloronaphthalene (CN) and tri-n-butylphosphate (TBP) have found to improve the performance of the sensors. The best performance was obtained for the membrane sensor having a composition of I:NaTPB:TBP:PVC in the ratio 6:4:100:90 (w/w; mg). The electrodes exhibit Nernstian slopes for Ni²⁺ ions over wide concentration ranges of 4.6 × 10^?7–1.0 × 10^?1 M for PME and 7.7 × 10^?8–1.0 × 10^?1 M for CGE with limits of detection of 2.7 × 10^?7 M for PME and 3.7 × 10^?8 M for CGE. The response time for PME and CGE was found to be 10 and 8 s respectively. The potentiometric responses are independent of the pH of the test solution in the pH range 3.0–8.0. The proposed electrodes revealed good selectivities over a wide variety of other cations including alkali, alkaline earth, transition and heavy metal ions. The coated graphite electrode was used as an indicator electrode in the potentiometric titration of nickel ion with EDTA and in direct determination in different fruit juices and wine samples.