Cupferron Complex Research Articles

Innovative Use of Carbon Nanotubes in Electrochemical Sensors for the Analysis of Europium in Samples from the Environment

An adsorptive stripping voltammetric method for the determination of trace europium(III) based on the adsorption of europium(III)−cupferron complex on the multiwall carbon nanotubes/spherical glassy carbon (MWCNTs/SGC) electrode modified with a lead film is presented. The method was optimized with respect to the main electrochemical parameters that affect the voltammetric determination (supporting electrolyte, pH, cupferron concentration, deposition potential and time). The calibration graph is linear from 5 × 10−9 to 5 × 10−7 mol l−1 with a correlation coefficient of 0.9993 for europium for a preconcentration time of 80 s. The detection limit for a preconcentration time of 80 s is as low as 1.3 × 10−9 mol l−1 for europium. To confirm the effectiveness of the developed procedure on the MWCNTs/SGC electrode, tests were also carried out on a glassy carbon electrode to compare the detection limits obtained. The developed procedure was tested for the effect of extraneous substances on the europium signal. The proposed method was successfully applied by studying natural samples and certified reference materials.

Stripping Voltammetry with Nanomaterials-based Electrode in the Environmental Analysis of Trace Concentrations of Tin.

A method for the voltammetric determination of tin using a multiwall carbon nanotubes/spherical glassy carbon (CNTs/SGC) electrode is described. The new procedure is based on the adsorptive accumulation of the Sn(II)-cupferron complex on a CNTs/SGC electrode modified with a lead film, followed by electrochemical reduction of the adsorbed species. The optimal experimental conditions include the use of 0.10 mol L-1 acetate buffer (pH 5.7), 4.0×10-4 M cupferron and 1.0×10-4 M Pb(II). The peak current is proportional to the concentration of Sn(II) over the range of 1.0×10-9 -1.0×10-7 M and the detection limit is 3.1×10-10 M for a 95 s accumulation time. The proposed method was used to determine tin in real samples and certified reference materials.

Combination of PbFE as an electrochemical sensor and cupferron as a complexing agent for the rapid determination of Mo(VI)

An analytical procedure regarding the trace determination of molybdenum in natural water samples by adsorptive stripping voltammetry (AdSV) using the in situ plated lead film electrode (PbFE) was described. The method is based on adsorptive accumulation of the Mo(VI)-cupferron complex at the PbFE surface. The optimum analytical conditions include the supporting electrolyte containing 0.2-mol L−1 acetic buffer pH = 5.3, 1.45 × 10−4-mol L−1 Pb(II), and 2.0 × 10−4-mol L−1cupferron. A linear response of Mo(VI) in the concentration range of 3.0 × 10−8 to 1.0 × 10−6 mol L−1 (r = 0.997) was obtained with detection limit of 9.0 × 10−9 mol L−1 using accumulation time of 50 s. The selectivity of the method was determined by investigating how the presence of foreign ions affects the determination of molybdenum. The interferences of surface-active substances and humic substances on the molybdenum voltammetric signal were precisely examined and effectively minimized by preliminary mixing with Amberlite XAD-7 resin. The application of the proposed procedure to the analysis of natural water samples was validated by the determination of molybdenum in certificate reference materials SPS-SW1 surface water, Bystrzyca river, tap, and mineral water.

Sequential determination of five heavy metal ions in Brazilian phosphate fertilizers and surface waters by stripping voltammetry

A method comprised of multi-detection steps for the sequential determination of uranium, cadmium, lead, thallium, and silver, using electroanalytical tools, is proposed herein. Firstly, adsorptive stripping voltammetry was applied to assay the U(VI)–cupferron complex in the differential pulse mode. In sequence, using the same aliquot of the sample, the quantifications of cadmium and lead were performed simultaneously by differential pulse anodic stripping voltammetry with the environmentally friendly bismuth film electrode. Due to the overlapping peaks of cadmium and thallium, the addition of EDTA enabled the determination of thallium by anodic stripping voltammetry. On employing the ex situ bismuth-film-modified electrode, the current intensity increased for the four heavy metal ions. After the removal of the bismuth film, silver was quantified at a glassy carbon electrode by anodic stripping voltammetry, as the last step of the multi-detection method. The method was successfully applied to phosphate fertilizer samples after open-vessel wet decomposition (HNO3/H2O2). Uranium was detected in the range of 36.2–144.0 mg kg−1. Cadmium and lead were detected in concentrations of up to 41.4 and 204.0 mg kg−1, respectively. The concentrations of thallium and silver were below the detection limits. Surface water samples (river water and lagoon water) were also analyzed with respect to the heavy metal ions. Validation was performed using the standard reference materials SRM-695 (phosphate fertilizer) and SRM-1643e (water).

Electrochemical Reduction of Vanadium(V)‐Cupferron Complex, VO(cupf)2OH

AbstractElectrochemical reduction of vanadium(V) complex with cupferron (N‐nitroso‐N‐phenylhydroxylamine), VVO(cupf)2OH, has been studied by polarography in wide potential range to verify the catalytic mechanism of electroreduction of coordinated cupferron ligand. Reduction of the complex was studied in the concentration range from 2 ⋅ 10−5 M to 10−3 M. Depending on the process conditions kinetics of catalytic reduction of coordinated cupferron is either controlled by adsorption step or governed by mixed control of diffusion and chemical reaction. Kinetic parameters of the reduction process are reported.Reduction of VVO(cupf)2OH complex is accompanied by adsorption and autoinhibition phenomena. V(II) ion in the surface bound complex of vanadium with cupferron catalyzes reduction of coordinated cupferronate ligands. In 1 mM solutions, the catalytic reduction of coordinated cupferron ligand shifts to more cathodic potentials due to formation of a monolayer of adsorbed vanadium(III)‐cupferron complexes. Reduction kinetics in the presence of tetraalkylammonium salt is consistent with multilayer cooperative adsorption of anionic vanadium(II)‐cupferron complex and tetraalkylammonium cations.

Evaluation of cupferron on the selective separation of gallium from aluminum by flotation: The separation mechanism

Aluminum is an impure element in acidic solutions obtained from gallium sources. Therefore, the selective separation of gallium from aluminum, using cupferron as a ligand (chelating agent) and sodium dodecyl sulfate as an anionic collector was investigated by flotation. The effect of the solution pH, the molar ratio of cupferron to gallium, the collector concentration, the impeller speed, the conditioning time and the flotation time on the selective separation of Ga(III) from Al(III) were studied. The results indicate that the chelating agent cupferron, efficiently separated gallium from aluminum, owing to the higher chelating strength of the interaction between Ga(III) and cupferron. The Ga(III)-cupferron complexes, formed in the presence and absence of SDS, were spectroscopically confirmed and characterized by Fourier transform infrared (FTIR), UV–visible spectroscopy and scanning electron microscopy coupled with energy dispersive X-ray (SEM/EDX). The bonding of cupferron with Ga(III) was considered to be as a bidentate ligand, and gallium formed 1:1.5 complexes with cupferron in aqueous solution. The separation mechanism of flotation was proposed owing to the formation of a physical interaction between the Ga(III)-cupferron complex and SDS.

A Fast and Simple Voltammetric Method Using a Lead Film Electrode for Determination of Ultra-Trace Concentration of Titanium in Environmental Water Samples

A fast, simple and highly sensitive adsorptive stripping voltammetric procedure for determination of trace quantity of Ti(IV) in natural water samples containing high concentrations of surfactants and humic substances was developed. The procedure was based on simultaneous lead film formation and adsorptive accumulation of the Ti(IV)-cupferron complex onto the in situ plated lead film electrode. Measurement conditions such as the concentration of cupferron, pH of the supporting electrolyte, conditions of lead film formation, accumulation potential and time were optimized. The interferences from dissolved surfactants and biosurfactant were eliminated by adding Amberlite XAD-7 resin to the voltammetric cell. Under optimum conditions the linear calibration plot for Ti(IV) was obtained in the range from 5.0 × 10−9 mol L−1 to 1.5 × 10−7 mol L−1 for the accumulation time of 60 s. The detection limit for the accumulation time of 60 s was about 1.7 × 10−9 mol L−1. The calibration graph obeyed the equation y = 0.487x + 0.843, where y and x were the peak current (μA) and Ti(IV) concentration (nmol L−1), respectively. The linear correlation coefficient was r = 0.996. The proposed method was successfully applied to determine titanium in the matrix-rich water sample and was validated in the course of Ti(IV) recovery determination from spiked natural water samples.

Ultratrace Determination of Indium in Natural Water by Adsorptive Stripping Voltammetry in the Presence of Cupferron as a Complexing Agent

A novel and highly sensitive adsorptive voltammetric procedure for direct determination of In(III) in natural water samples was introduced. The method is based on cathodic adsorptive stripping voltammetry of the In(III)-cupferron complex at a renewable mercury film silver based electrode (Hg(Ag)FE). Experimental conditions were established and included: 0.1 mol L−1 acetate buffer (pH = 5.5), 5 × 10−5 mol L−1 cupferron, accumulation potential 0 V. The calibration graph was linear from 5 × 10−10 mol L−1 to 2 × 10−8 mol L−1 with the correlation coefficient of 0.9993. Limit of detection (LOD) and limit of quantification (LOQ) for preconcentration time of 30 s were 1.5 × 10−10 mol L−1 and 5 × 10−10 mol L−1, respectively. The interference of surface active substances and humic substances on the indium voltammetric signal was precisely examined, and effectively minimalized. The application of the procedure to the analysis of natural water samples was validated by the determination of indium in certificate reference materials SPS-WW1 Wastewater and SPS-SW1 Surface Water, river water, rain water and tap water.

Application of a Lead Film Electrode in Adsorptive Stripping Voltammetry for the Determination of Indium Trace in Water Samples

The in situ plated lead film electrode for adsorptive stripping voltammetric measurements of trace levels of In(III) was proposed. The optimum electroanalytical performance was achieved in electrolyte solution comprising 0.2 mol L−1 acetate buffer pH = 4.5, 5 × 10−5 mol L−1 Pb(II), 5 × 10−4 mol L−1 cupferron. The lead film electrode formation and the In(III)–cupferron complex adsorption on the electrode were performed using the following potentials −1.6 V (10 s) and −0.7 V (60 s) versus Ag/AgCl reference electrode, respectively. The procedure exhibited excellent parameters in the presence of dissolved oxygen with the calculated detection limit of 1.65 × 10−10 mol L−1, repeatability with RSD of 4.4% (n = 5), and linear response in the examined concentration range from 5 × 10−10 to 2 × 10−7 mol L−1. The application of the proposed procedure was successfully examined by recovery of In(III) from spiked natural water samples.

Determination of trace amounts of Ga(III) by adsorptive stripping voltammetry with in situ plated bismuth film electrode

The determination of trace gallium using adsorptive stripping voltammetry at an in situ plated bismuth film electrode was described. The method was based on simultaneous film formation and the Ga(III)–cupferron complex preconcentration at −0.65V and its cathodic stripping during the potential scan. The effect of Bi(III) and cupferron concentration, the influence of deposition potential and time, and the scan rate on the determination of Ga(III) were studied. A linear response in the concentration range of 3×10−10 to 3×10−7molL−1 (r=0.998) was obtained with detection limit of 1.05×10−10molL−1 using accumulation time of 180s. Finally, the bismuth film electrode was successfully applied for the determination of Ga(III) in certified reference material seawater NASS-5 with satisfactory results.

Sequential Voltammetric Determination of Uranium, Cadmium and Lead by Using the ex situ Bismuth Film Electrode: Application to Phosphate Fertilizers

AbstractA sequential voltammetric procedure for the determination of uranium, cadmium and lead was investigated at an ex situ bismuth film electrode (BiFE). First, the adsorptive stripping voltammetry was applied to assay the U(VI)‐cupferron complex in the differential pulse mode (detection limit of 1.0 µg L−1, 200 s accumulation time). Through the manipulation of the same aliquot of the sample, efforts were made to quantify cadmium and lead by square wave anodic stripping voltammetry. Detection limits of 2.03 µg L−1 for Cd (II) and 2.43 µg L−1 for Pb (II) were calculated (100 s accumulation time). The methodology was successfully applied to phosphate fertilizer samples after open vessel wet decomposition (HNO3/H2O2). The following value ranges were evaluated: U (VI) 37.2–150 mg kg−1, Pb (II) 78.3–204 mg kg−1 and Cd (II) 44.1–71.6 mg kg−1. Validation was performed by using the standard reference materials SRM‐695 – phosphate fertilizer – and SRM‐1643e – water.

Adsorptive Cathodic Stripping Voltammetric Method for Determination of Gallium Using an In Situ Plated Lead Film Electrode

AbstractThe in situ plated lead film electrode was proposed for the first time for adsorptive stripping voltammetric determination of gallium in water samples. The method was based on simultaneous lead film formation and Ga(III)‐cupferron complex preconcentration at −0.7 V and its cathodic stripping during the potential scan. The composition of the supporting electrolyte, cupferron concentration, conditions of lead film formation, potential and time of accumulation were studied in detail. Under optimum conditions the limit of detection was 3.8×10−9 mol L−1. The proposed procedure was validated in the course of Ga(III) determination in waste water certified reference materials.

Six-coordinate ferric porphyrins containing bidentate N-t-butyl-N-nitrosohydroxylaminato ligands: structure, magnetism, IR spectroelectrochemisty, and reactivity.

NONOates (diazeniumdiolates) containing the [X{N2O2}](-) functional group are frequently employed as nitric oxide (NO) donors in biology, and some NONOates have been shown to bind to metalloenzymes. We report the preparation, crystal structures, detailed magnetic behavior, redox properties, and reactivities of the first isolable alkyl C-NONOate complexes of heme models, namely (OEP)Fe(η(2)-ON(t-Bu)NO) (1) and (TPP)Fe(η(2)-ON(t-Bu)NO) (2) (OEP = octaethylporphyrinato dianion, TPP = tetraphenylporphyrinato dianion). The compounds display the unusual NONOate O,O-bidentate binding mode for porphyrins, resulting in significant apical Fe displacements (+0.60 Å for 1, and +0.69 Å for 2) towards the axial ligands. Magnetic susceptibility and magnetization measurements made from 1.8-300 K at magnetic fields from 0.02 to 5 T, yielded magnetic moments of 5.976 and 5.974 Bohr magnetons for 1 and 2, respectively, clearly identifying them as high-spin (S = 5/2) ferric compounds. Variable-frequency (9.4 GHz and 34.5 GHz) EPR measurements, coupled with computer simulations, confirmed the magnetization results and yielded more precise values for the spin Hamiltonian parameters: g(avg) = 2.00 ± 0.03, |D| = 3.89 ± 0.09 cm(-1), and E/D = 0.07 ± 0.01 for both compounds, where D and E are the axial and rhombic zero-field splittings. IR spectroelectrochemistry studies reveal that the first oxidations of these compounds occur at the porphyrin macrocycles and not at the Fe-NONOate moieties. Reactions of 1 and 2 with a histidine mimic (1-methylimidazole) generate RNO and NO, both of which may bind to the metal center if sterics allow, as shown by a comparative study with the Cupferron complex (T(p-OMe)PP)Fe(η(2)-ON(Ph)NO). Protonation of 1 and 2 yields N2O as a gaseous product, presumably from the initial generation of HNO that dimerizes to the observed N2O product.

An adsorptive stripping voltammetry procedure for ultra-trace determination of U(VI) using double accumulation step on two lead-film working electrodes

We report a very sensitive stripping voltammetric procedure for determination of ultra-trace quantity of U(VI) in water samples. A very low detection limit was achieved owing to the application of a new construction of the voltammetric electrode cell with two built-in working electrodes that differed significantly in their surface area. The procedure was based on the double adsorptive accumulation of the U(VI)-cupferron complex onto two lead film working electrodes. Under optimal conditions the detection limit for accumulation time of 120s for the big electrode and 120s for the small electrode was about 3.1×10–11molL−1, whereas for accumulation time of 480s for the big electrode and 240s for the small electrode it was about 1.1×10–11molL−1. The proposed method was successfully validated using certified reference material seawater NASS-5.

Application of Cupferron‐lead(II) Complex for the Electrochemical Determination of dsDNA

AbstractBased on the interaction of cupferron and lead(II) complex [Cup‐Pb(II)] with double‐stranded DNA (dsDNA) a new voltammetric method for the detection of DNA was described in this paper. In pH 4.0 HAc‐hexamine buffer solution, [Cup‐Pb(II)] complex showed a sensitive second order derivative polarographic reductive peak at ‐0.554 V (vs. SCE). After the addition of dsDNA into [Cup‐Pb(II)] mixture solution the reductive peak current decreased with the positive shift of reductive peak potential, which was the typical characteristic of intercalation mode. Under the optimum conditions, the decrease of reductive peak current was directly proportional to the dsDNA concentration in the range from 1.0 to 25.0 mg/L with the linear regression equation as ΔIp″ (nA) = 129.30 + 62.51 C (mg/L) (n = 13, γ = 0.991). The detection limit of 0.90 mg/L (3σ) and the relative standard derivation (RSD) of 2.43% for 10 parallel determinations of 10.0 mg/L dsDNA were found. The method was successfully applied to synthetic samples with good results, and the stoichiometry of dsDNA with [Cup‐Pb(II)] complex was calculated by the voltammetic data with the binding number as 2 and the binding constant as 2.82 × 109.

Determination of trace titanium(iv) by differential pulse catalytic adsorptive stripping voltammetry at a bismuth film electrode

The differential pulse catalytic adsorptive stripping voltammetry behavior of titanium(IV)–cupferron system at bismuth coated glassy carbon electrode (BiFE) has been investigated. In the piperazine-N,N′-bis(2-ethanesulfonic acid) (PIPES)–KCl solution (pH 6.4), the deposition potential at −0.70 V for 120 s, a well-defined and sensitive stripping peak of Ti(IV)–cupferron complex at −0.97 V (vs. SCE) was observed. Under optimized conditions, the peak current was linear to the concentration of Ti(IV) in the range from 10 to 60 μg L−1 with the detection limit of 0.5 μg L−1. To further demonstrate its possible application, the method was successfully applied to detect trace Ti(IV) in hair and water samples with satisfactory results.

Adsorptive stripping voltammetric determination of trace amounts of lead in environmental water samples with complicated matrix

A sensitive, simple and fast adsorptive stripping voltammetric procedure for trace determination of lead in environmental water samples has been developed. The method is based on adsorptive accumulation of the Pb(II)-cupferron complex onto a hanging mercury drop electrode, followed by the reduction of the adsorbed species by a voltammetric scan using differential pulse modulation. The interference from surface active substances was eliminated by adsorption of interferents onto an Amberlite XAD-16 resin. Optimum conditions for removing the surfactants by mixing the analysed sample with resin were evaluated. The accuracy of the method was tested by analyzing certified reference material (SPS-WW1 Waste Water).

Understanding the thermal decomposition effects in TOPO capped ZnO nanocrystals

Different shapes and sizes of TOPO-capped ZnO nanostructures have been obtained by the decomposition of the cupferron complex in the presence of tri-n-octylphosphine oxide (TOPO) under different conditions. The precursor : TOPO ratio, the order of reactants and thermal decomposition temperature play important roles in determining of the shape and size of nanoparticles. Particle size was evaluated using TEM images and effective mass approximation method from UV-vis spectroscopy to be about 1–80 nm. Changes in luminescence intensities have been measured for ZnO capped by TOPO after different growth temperatures. FT-IR, 1H-NMR and {1H}35P-NMR results confirm the contribution of coordinated TOPO persists longer, but at a high temperature only the broad background peaks remain. FE-SEM images of ZnO samples obtained by hydrothermal treatment have been shown to have nano-leaf like and nanorod morphology. The morphology of the ZnO nanorod and nano-leaf are related to the crystal structure and the velocities of crystal growth in different directions. XRD patterns were shown with increasing thermal decomposition temperature, the diffraction peak intensity of faces [0002] and [101] were obviously lower and the peak intensity of polar face [100] increases. EDX analysis was indicated ZnO nanocrystal without impurity at 600 °C.

Direct Determination of Cadmium Traces in Natural Water by Adsorptive Stripping Voltammetry in the Presence of Cupferron as a Chelating Agent

AbstractA sensitive, simple and fast adsorptive stripping voltammetric procedure for trace determination of cadmium in natural samples containing high concentrations of surface active substances and humic substances has been developed. The method is based on adsorptive accumulation of the Cd(II)‐cupferron complex onto a hanging mercury drop electrode, followed by the reduction of the adsorbed species by a voltammetric scan using differential pulse modulation. The detection limit was 3×10−10 mol L−1 (33.6 ng L−1) with an accumulation time 30 s. The procedure was applied to the determination of Cd(II) in natural water samples without any pre‐treatment with satisfactory results.

Determination of molybdenum in biological samples by flame atomic spectrometry after preconcentration on activated carbon

Molybdenum is well known for its toxic effects, although it is also essential for N2-fixing cyanobacteria and several enzymes. This study proposes a simple and accurate procedure for separation, preconcentration, and determination of trace amounts of molybdenum in biological samples by flame atomic absorption spectrometry. It is based on complexation of Mo by cupferron and sorption onto activated carbon. Effects of parameters such as pH, stirring time, and amounts of activated carbon and cupferron on recovery were examined. The results demonstrated that Mo at pH range of 2.5–3.5 was quantitatively sorbed onto activated carbon as its cupferron complex. The optimum stirring time was found to be 30 min. The relative standard deviation was found to be 12% for 200 cm3 50 ng/cm3 Mo using 10 replicate preconcentration procedures. The limits of detection and quantification were found to be 1.0 and 3 ng/cm3, respectively, by preconcentration of 200 cm3 initial sample to 2 cm3 final volume. As a result, an enrichment factor of 100-fold was achieved. The proposed preconcentration procedure was applied to determine Mo in biological samples such as vegetables, milk, and animal liver. The molybdenum concentrations were found (as μg/dm3 or μg/kg) in the range of 70–5,500 for plants, 3–124 for milk and milk powder, and 960 for liver samples.