Study on simultaneous measurements of trace gallium(III) and germanium(IV) by adsorptive stripping voltammetry using mercury film electrode

Simultaneous adsorptive stripping voltammetric method for the determination of trace gallium(III) and germanium(IV) based on the adsorption of gallium(III) and germanium(IV)-catechol complex on the cyclic renewable mercury film silver based electrode (Hg(Ag)FE) is presented. The calibration graph is linear from 1.25 nM (0.09 μg L⁻¹) to 90 nM (6.27 μg L⁻¹) with correlation coefficient of 0.999 for gallium and from 2.5 nM (0.18 μg L⁻¹) to 160 nM (12.3 μg L⁻¹) with correlation coefficient of 0.998 for germanium for a preconcentration time of 30 s. The detection limit for a preconcentration time of 60 s is as low as 25 ng L⁻¹ for gallium and 58 ng L⁻¹ for germanium. The proposed method was successfully applied by studying the natural samples and simultaneous recovery of Ga(III) and Ge(IV) from spiked water and sediment samples.     

A new method for the simultaneous determination of Fe(III), Cu(II), Pb(II), Zn(II), Cd(II), and Ni(II) in wine using differential pulse polarography

A new and simple differential pulse polarographic method for the analysis of wine has been established. With this method, it was possible to determine simultaneously six trace elements in wine. There was no need for time consuming extraction and separation procedures with danger of contamination. The polarogram of wet digested wine was taken initially in pH 2 acetate buffer and Pb, Cd, and Zn were determined by standard additions. Ethylene diamine tetraacetic acid (EDTA) was added and pH was increased to six by addition of NaOH. Fe and Cu were determined subsequently. The ammonia buffer, pH 9.5, was identified as the best medium for separation and determination of Ni and Zn. The quantities of trace elements were found as Cu 290 ± 20 μg L⁻¹, Fe 8960 ± 50 μg L⁻¹, Pb 148 ± 17 μg L⁻¹, Cd 16 ± 8 μg L⁻¹, Zn 460 ± 25 μg L⁻¹, and Ni 78 ± 17 μg L⁻¹.     

Surfactant-Mediated Catalytic Determination of Fe(II) in Herbal and Pharmaceutical Products

In the present work, the catalyzed oxidation of neutral red (NR) by bromate was used to work out a kinetic-based analytical method as an alternative technique for the determination of Fe(II) in real and synthetic samples. A use of a surfactant, N-dodecylpyridinium chloride enhanced the sensitivity of the reaction by becoming involved in the reaction mechanism and providing a more suitable reaction environment. The iron-catalyzed oxidation of NR with potassium bromate was studied kinetically by using a fixed time method. The reaction was followed by measuring the decrease in absorbance at 535 nm. The use of a surfactant in the analytical run showed a five times increase in the sensitivity of the method. It served as a ready reservoir of NR by increasing its solubilization. The salt effect, pH, and reagent concentration were also investigated to achieve a more selective and sensitive analytical procedure. Under optimized conditions (4.2 × 10⁻⁵ mol L⁻¹ NR, 1.4 × 10⁻³ mol L⁻¹ KBrO₃, 1.5 × 10⁻² mol L⁻¹ cationic surfactant, 0.5 mol L⁻¹ LiCl and pH 2.60 at 30 °C), iron(II) was determined in the range 0.1–0.5 μg mL⁻¹ with a detection limit of 0.019 μg mL⁻¹ and a relative standard deviation (n = 6) 1.02% for 0.2 μg mL⁻¹ Fe(II). The influence of foreign ions on the accuracy of the results was investigated. The developed method is extremely sensitive, selective and simple. The method was applied successfully to the determination of iron in the herbal pharmaceutical and synthetic samples. The results showed good agreement with those obtained by atomic absorption spectrophotometry.

Effect of Bi(III) concentration on the stripping voltammetric response of in situ bismuth-coated carbon paste and gold electrodes

The effect of Bi(III) concentration (over the wide concentration range of 10⁻⁷ to 10⁻⁴ M) on the determination of Pb and Cd metal ions (in the 10⁻⁸ to 10⁻⁵ M range), by means of anodic stripping voltammetry (ASV) at in situ bismuth-coated carbon paste (CPE) and gold electrodes, has been studied. It is shown that in square wave anodic stripping voltammetry (SWASV) experiments the sensitivity of the technique generally depends on the Bi(III)-to-metal ion concentration ratio. It was found that, unlike the usually recommended at least 10-fold Hg(II) excess in anodic stripping experiments at in situ prepared mercury film electrodes, Bi(III)-to-metal ion ratios less than 10 are either optimal or equally effective at CPE and Au electrode substrates. Detection limits down to 0.1 μg L⁻¹ for Pb(II) and 0.15 μg L⁻¹ for Cd(II) were estimated at CPEs under conditions of small or moderate Bi(III) excess. Depending on Bi(III) concentration and deposition time, multiple stripping peaks attributed to Bi were recorded (especially in the case of Au substrates), indicating various forms of Bi deposits.     

Square-wave adsorptive stripping voltammetric determination of candesartan cilexetil in pharmaceutical formulations

A sensitive, simple and rapid square-wave adsorptive stripping voltammetric method was developed and validated for the determination of candesartan cilexetil in pharmaceutical formulations. The proposed method was based on electrochemical reduction of candesartan cilexetil at a hanging mercury drop electrode in phosphate buffer at pH 5.0. A well-defined reduction peak was observed at −1340 mV with 30 s of accumulation time and −1100 mV of accumulation potential. Under these optimized conditions, the square-wave adsorptive stripping voltammetric peak current showed a linear correlation on drug concentration over the range of 0.25–1.34 μg mL⁻¹ with a correlation coefficient of 0.9986 for the proposed method. The detection and quantitation limits for this method were 1 × 10⁻² and 2.5 × 10⁻¹ μg mL⁻¹, respectively. The results obtained for intra-day and inter-day precision (as RSD%) were between 1.10 and 3.90%. This method was applied successfully for the determination of candesartan cilexetil in its tablet dosage forms with mean recoveries of 101.13 ± 0.78% with RSD of 2.06% for 8 mg tablet and 99.84 ± 0.89% with RSD of 2.36% for 16 mg tablet. The results obtained from the developed square-wave adsorptive stripping voltammetric method were compared with those obtained by the analytical method reported in the literature.     

Determination of cadmium (II) using H<Subscript>2</Subscript>O<Subscript>2</Subscript>-oxidized activated carbon modified electrode

Pristine activated carbon (AcC) was oxidized by H₂O₂ under ultrasonic conditions. Compared with pristine AcC, the H₂O₂-oxidized AC possesses higher accumulation ability to trace levels of Cd²⁺. Based on this, a highly sensitive, simple and rapid electrochemical method was developed for the determination of Cd²⁺. In 0.01 mol L⁻¹ HClO₄ solution, Cd²⁺ was effectively accumulated at the surface of H₂O₂-oxidized AcC modified paste electrode, and then reduced to Cd under −1.10 V. During the following potential sweep from −1.10 to −0.50 V, reduced Cd was oxidized and a sensitive stripping peak appears at −0.77 V. The stripping peak current of Cd²⁺ changes linearly with concentration over the range 5.0 × 10⁻⁸ to 5.0 × 10⁻⁶ mol L⁻¹. The limit of detection was found to be 3.0 × 10⁻⁸ mol L⁻¹ for 2-min accumulation. Finally, this new sensing method was successfully used to detect Cd²⁺ in waste water samples.     

Cationic Mobility Via Cation-Exchange Mechanism on Poly(8-Hydroxyquinoline) Matrix

The insertion of Al(III) cation into a poly(8-Hydroxyquinoline) (PHQ) instead of some metal ions such as Co(II), Ni(II), Zn(II) or Fe(III) ions via cation-exchange mechanism has been studied by several techniques. The presence of Al(III) and the absence of Co(II) cations has been proved by elemental analysis of the polymer chelates product. Molecular mechanics (MM+) calculations showed that the potential energy (PE, kJ mol⁻¹) of the optimum molecular geometric structure (OMG) of the PHQ–Al(III) matrix is about seventy-six (76.185) greater than the PE of the PHQ–Co(II) complex. The TGA thermograms show that the PHQ–Al(III) matrix is thermally unstable than the PHQ–Co(II) complex under the same conditions. These observations indicate that the PHQ–Al(III) is expanded coil-like form. So, the thermal decomposition of PHQ–Al(III) complex is easy than the compacted coil-likes form of PHQ–Co(II) complex. The incorporation of Al(III) ion via cation-exchange properties have been investigated by spectrophotometric technique. The decrease of the absorbance at about ~370 nm of PHQ–Co(II) complex associated with increasing concentration of Al(III) revealed the replacement of that metal ion by Al(III) into PHQ chain. The cation-exchange constant (K _ex) of the divalent ions [Ni(II), Co(II), Cr(II), Zn(II), Mn(II), Mg(II) and Cu(II)] from PHQ–M(II) by the additions of Al(III) according to the following series: Ni(II) > Co(II) > Cr(II) > Cu(II) > Zn(II) > Mn(II) > Mg(II).     

Electrocatalytic oxidation of hydroxylamine at Ni(II)-morin complex modified carbon nanotube paste electrode

A modified electrode, nickel(II)-morin complex modified multi-wall carbon nanotube paste electrode (Ni(II)-MR-MWCNT-PE), has been fabricated by electrodepositing Ni(II)-MR complex on the surface of MWCNT-PE in alkaline solution. The Ni(II)-MR-MWCNT-PE exhibits the characteristic of improved reversibility and enhanced current responses of the Ni(III)/Ni(II) couple compared with Ni(II)-MR complex modified carbon paste electrode (CPE). It also shows better electrocatalytic activity toward the oxidation of hydroxylamine than the Ni(II) modified MWCNT-PE (Ni(II)-MWCNT-PE) and Ni(II)-MR-CPE. Kinetic parameters such as the electron transfer coefficient α, rate constant k _s of the electrode reaction and the catalytic rate constant k _cat of the catalytic reaction are determined. Moreover, the catalytic currents present linear dependence on the concentration of hydroxylamine from 2.5 × 10⁻⁶ to 4.0 × 10⁻⁴ mol L⁻¹ by amperometry. The detection limit and sensitivity are 8.0 × 10⁻⁷ mol L⁻¹ and 56.2 mA L mol⁻¹, respectively. The modified electrode for hydroxylamine determination is of the property of simple preparation, good stability, fast response and high sensitivity.     

Insights into the simultaneous chronopotentiometric stripping measurement of indium(III), thallium(I) and zinc(II) in acidic medium at the in situ prepared antimony film carbon paste electrode

The simultaneous measurement of microgram per liter concentration levels of indium(III), thallium(I) and zinc(II) at the antimony film carbon paste electrode (SbF-CPE) is demonstrated. The antimony film was deposited in situ on a carbon paste substrate electrode and employed in chronopotentiometric stripping mode in deoxygenated solutions of 0.01 M hydrochloric acid (pH 2). The chronopotentiometric stripping performance of the SbF-CPE was studied and compared with constant current chronopotentiometric stripping and anodic stripping voltammetric operation. In comparison with its bismuth and mercury counterparts, the SbF-CPE exhibited advantageous electroanalytical performance; namely, at the bismuth film electrode, the measurement of zinc(II) was practically impossible due to hydrogen evolution, whereas the mercury film electrode exhibited a poorly developed signal for thallium(I). The SbF-CPE revealed favorable calculated LoDs (3σ) of 1.4 μg L⁻¹ for thallium(I) and 2.4 μg L⁻¹ for indium(III) along with good linear response in the examined concentration range from 10 to 100 μg L⁻¹ with correlations coefficients (R²) of 0.992 for thallium(I) and 0.994 for indium(III) associated with a 120 s deposition time. The chronopotentiometric stripping performance of the SbF-CPE was characterized also by satisfactory reproducibility of 1.62% for indium(III), 3.96% for thallium(I) and 2.11% for zinc(II) (c = 40 μg L⁻¹, n = 11).     

Fabrication of carbon nanotube and dysprosium nanowire modified electrodes as a sensor for determination of curcumin

Two sensitive sensors for determination of curcumin (CM) were described. CM can be detected using multiwall carbon nanotube (MWCNT)-modified electrodes and dysprosium nanowire carbon paste electrode using the technique of adsorptive stripping voltammetry (AdSV) in stationary solution and the fast Fourier transform voltammetry at the flowing solution. Both electrodes did show less passivation effect that occurs on the unmodified electrodes and displayed better stability and reproducibility. This electrode enabled selective determination of CM in the presence of interfering species. Under optimized conditions, CM could be detected over a linear range with a detection limit of 5.0 × 10⁻⁹ mol L⁻¹ and 5.0 × 10⁻¹⁰ mol L⁻¹ for the traditional square wave and fast Fourier transform square wave voltammetry (FFTSWV) with RSD between 0.2 and 0.5%. Comparison with other reported methods showed these studies are about 100 times more sensitive than previous ones. Good selectivity and high sensitivity obtained by Square wave voltammetry can open new possibilities of direct CM determination.     

Effect of electrolyte concentration on morphology,microstructure and electrochemical impedance of anodic oxide film on titanium alloy Ti-10V–2Fe–3Al

Anodic oxide films were fabricated on titanium alloy Ti-10V–2Fe–3Al in ammonium tartrate solutions at the concentrations: 1, 3, 5, 10 and 15 g L⁻¹. The morphological characteristics and microstructures of the films of the alloy were studied by optical microscopy (OM) and Raman spectroscopy (Raman), respectively. The electrochemical impedances of the films in 0.5 mol L⁻¹ H₂SO₄ solution were investigated by electrochemical impedance spectroscopy (EIS). It was showed that different electrolyte concentrations led to different change rates of anodizing forming voltage. The change rate significantly affected the morphology, microstructure and electrochemical impedance of anodic oxide film. When electrolyte concentration was 5 g L⁻¹, anodic oxide film was the most uniform, exhibited by the least and smallest breakpoints on the film. In addition, the amount of crystal phase of the film was the largest at 5 g L⁻¹, showed by the highest intensity of Raman peaks. Furthermore, the electrochemical impedance of the film of the alloy was the greatest at 5 g L⁻¹, demonstrated by the highest values of polarization resistances and lowest values of capacitances. These phenomenon were associated with the minimum value of the change rate of anodizing forming voltage at 5 g L⁻¹.     

Lithographically fabricated disposable bismuth-film electrodes for the trace determination of Pb(II) and Cd(II) by anodic stripping voltammetry

This work reports the photolithographic fabrication of disposable bismuth-film electrodes (BiFEs) using a thin-film deposition approach. The deposition of the bismuth layer was carried out by sputtering of metallic bismuth on a silicon substrate while the exact geometry of the BiFEs was produced by photolithography. The utility of these sensors was tested for the simultaneous trace determination of Cd(II) and Pb(II) by square wave anodic stripping voltammetry (SWASV). Using the selected conditions, the limits of detection were 0.5 μg l⁻¹ for Pb(II) and 1 μg l⁻¹ for Cd(II) at a preconcentration time of 4 min. The interference caused by Cu(II) was alleviated by the addition of ferrocyanide in the sample solution. Finally, the proposed BiFEs were successfully applied to the determination of Cd and Pb in a phosphate fertilizer and a river water sample. These sensors offer wide scope for trace metal analysis in terms of mass-production of mercury-free disposable sensors with performance comparable to their mercury counterparts.     

Separation and direct detection of heavy lanthanides using new ion-exchange chromatography: fast Fourier transform continuous cyclic voltammetry system

In this study, possibilities of heavy lanthanides (Ho³⁺, Er³⁺, Tm³⁺, Yb³⁺, and Lu³⁺) separation on Nucleosil 100-5-SA, an ion-exchange column, was investigated. Separation of lanthanides was carried out using an isocratic program of α-hydroxyisobutyric acid (HIBA) eluent. Fast Fourier transform continuous cyclic voltammetry (FFT-CCV) at a gold microelectrode was used as the detection method. Simplicity, high precision and accuracy, time efficiency, and being economic are advantages of the developed technique in comparison with the previous reported ones. In addition, removal of oxygen from the test solution is not required, the detection limit is suitable and the technique is fast enough for determination of compounds in a wide variety of chromatographic methods. The waveform potential was continuously applied on an Au disk microelectrode (12.5 μm in radius). The influence of HIBA concentration as well as pH of eluent was optimized. The best performance of the method was obtained at pH of 4.0, scan rate of 30 V s⁻¹, accumulation potential of −300 mV, and accumulation time of 0.3 s. The proposed method displays a linear dynamic range of 140 and 18,000 μg L⁻¹ and a detection limit of 50 μg L⁻¹. Precision, inter-day precision, and accuracy of the assay were reported too. A comparative evaluation of heavy lanthanides distributed in a sophisticated monazite and xenotime minerals solutions was carried out using both FFT-CCV, and inductively coupled plasma-atomic emission spectrometry (ICP-AES).     

Carbon nanotube-modified glassy carbon electrode for anodic stripping voltammetric detection of Uranyle

A multi-wall carbon nanotube (MWNT) modified glassy carbon electrode (GCE) is described for the measurement of trace levels of uranium by anodic stripping voltammetry. In a pH 4.4 NaAc-Hac buffer containing 0.010 mol L⁻¹ Mg(NO₃)₂, UO₂ ²⁺ was adsorbed onto the surface of a MWNT film coated glassy carbon electrode and then reduced at −0.40 V vs. Ag/AgCl. During the positive potential sweep the reduced uranium was oxidized and a well-defined stripping peak appeared at +0.20 V vs. Ag/AgCl. Low concentrations of Mg²⁺ significantly enhanced the stripping peak currents since they induced UO₂ ²⁺ to adsorb at the electrode surface. The response was linear up to 1.2 × 10⁻⁷ mol L⁻¹ and the relative standard deviation at 2.0 × 10⁻⁸ mol L⁻¹ uranium was 5.2%. Potential interferences were examined. The attractive behavior of the new “mercury-free” uranium sensor holds promise for on-site environmental and industrial monitoring of uranium.     

Novel bismuth/multi-walled carbon nanotubes-based electrochemical sensor for the determination of neuroprotective drug cilostazol

A very sensitive electrochemical sensor has been developed by modification of glassy carbon electrode (GCE) with nanoparticles of bismuth (III) oxide (Bi₂O₃) and multi-walled carbon nanotubes (MWCNTs). The sensor was applied for the determination of cilostazol, cyclic nucleotide phosphodiesterase inhibitors in pharmaceutical formulation and human plasma. The voltammetric responses were compared with those obtained at bare GCE under optimum conditions. The cyclic and square-wave voltammograms of cilostazol showed 3.3 and 4.9 times enhancement in the oxidation peak current at MWCNTs–Bi₂O₃/GCE as compared to a bare GCE. Bi₂O₃–MWCNTs/GCE showed a linear response for cilostazol in standard solution over the concentration range of 0.8–13 μg mL⁻¹ with the detection limit 0.76 μg mL⁻¹, whereas human plasma over the concentration range 0.8–12.5 μg mL⁻¹ with the detection limit 0.66 μg mL⁻¹.     

Preparation of Cadmium(II) Oxide Nanoparticles from a New One-Dimensional Cadmium(II) Coordination Polymer Precursor; Spectroscopic and Thermal Analysis Studies

A one-dimensional Cd(II) coordination polymer containing 2-pyridinecarboxylate (2-pyc⁻) and iodide anions [Cd(μ-2-pyc)(μ-I)] _n (1), is synthesized and characterized by elemental analysis, IR spectroscopy, thermal analysis and X-ray crystallography. The single-crystal X-ray data show that the coordination number for the Cd²⁺ ion is five. The thermal stability of 1 was studied by thermogravimetry and differential thermal analyzes. Cd(II)O nanoparticles were prepared by direct calcination of 1 at different temperatures. The Cd(II)O nanoparticles were characterized by X-ray powder diffraction and scanning electron microscopy. The results show that the morphology of the Cd(II)O nanoparticles is dependent upon the thermolysis temperature.     

One- and Two-Dimensional Cadmium(II) Tetracyanonickelate(II) Coordination Polymers With Imidazole and 2-Methylimidazole Ligands

Two novel cyano-bridged heteropolynuclear complexes, [Cd(im)₄Ni(μ-CN)₂(CN)₂] _n (1) and [Cd(mim)₂Ni(μ-CN)₄] _n (2) (im: imidazole and mim: 2-methylimidazole), have been synthesized and characterized. In 1, the trans-directed cyanide ligands of [Ni(CN)₄]²⁻ anions link two [Cd(im)₄]²⁺ units, whereas in 2, all the cyanide groups take part in bonding with two adjacent [Cd(mim)₂]²⁺ units, resulting 1D and 2D coordination polymers, respectively. The coordination environment of the Cd(II) ion described as distorted octahedral geometry, whereas around the Ni(II) centre had square planar geometry in both complexes. The crystals packing of 1 and 2 were a composite of hydrogen bonding, π···π and C–H···Ni interactions.     

Simultaneous preconcentration of Cd(II), Cu(II) and Pb(II) on Nano-TiO2 modified with 2-mercaptobenzothiazole prior to flame atomic absorption spectrometric determination

Nano-TiO₂ modified with 2-mercaptobenzothiazole (MBT) was investigated as a new adsorbent for preconcentration of Cd(II), Cu(II) and Pb(II). The metal ions are adsorbed onto nano-TiO₂-MBT, eluted by nitric acid and determined by flame atomic absorption spectrometry. The parameters affecting the adsorption were investigated. Under optimized conditions, the calibration curves were linear in the range of 0.2–25.0, 0.2–20.0, and 3.0–70.0 ng mL⁻¹ for cadmium, copper and lead, respectively. The limits of detection for Cd(II), Cu(II) and Pb(II) were 0.12, 0.15 and 1.38 ng mL⁻¹, respectively. The method was applied to determination of Cd(II), Cu(II) and Pb(II) in water and ore samples.     

A Novel Twofold Interpenetrating 2D (3,5)-Connected Cd(II) Coordination Framework with (52.6)(55.64.7) Topology

The self-assembly of 4′-(4-carboxyphenyl)-4,2′:6′4″-terpyridine (HL) with Cd(II) cation afforded one novel twofold interpenetrating 2D coordination polymer, [Cd(L)₂(H₂O)_1.5] _n . In this compound, the Cd(II) atoms as 5-connected nodes are linked by the bridging ligands L acting as both linear connectors and 3-connected nodes to form a novel (3, 5)-connected 2D framework with the (5².6)(5⁵.6⁴.7) topology. Two equivalents of such 2D framework interpenetrate with each other to form a more complicated supramolecular network. Furthermore, fluorescent measurement on the powder sample shows that the complex strongly emits at 399 nm with the excitation of 331 nm.     

Anodic stripping voltammetric measurement of trace heavy metals at antimony film carbon paste electrode

The antimony film carbon paste electrode (SbF-CPE) was prepared in situ on the carbon paste substrate electrode as a “mercury-free” electrochemical sensor. Its aptitude for measuring some selected trace heavy metals has been demonstrated in combination with square-wave anodic stripping voltammetry in non-deaerated model solutions of 0.01 M hydrochloric acid with pH 2. Some important operational parameters, such as deposition potential, deposition time, and concentration of antimony ions were optimized, and the electroanalytical performance of the SbF-CPE was critically compared with both bismuth film carbon paste electrode (BiF-CPE) and mercury film carbon paste electrode (MF-CPE) using Cd(II) and Pb(II) as test metal ions. In comparison with BiF-CPE and MF-CPE, the SbF-CPE exhibited superior electroanalytical performance in more acidic medium (pH 2) associated with favorably low hydrogen evolution, improved stripping response for Cd(II), and moreover, stripping signals corresponding to Cd(II) and Pb(II) at the SbF-CPE were slightly narrower than those observed at bismuth and mercury counterparts. In addition, the comparison with antimony film electrode prepared at the glassy carbon substrate electrode displayed higher stripping current response recorded at the SbF-CPE. The newly developed sensor revealed highly linear behavior in the examined concentration range from 5 to 50 μg L⁻¹, with limits of detection (3σ) of 0.8 μg L⁻¹ for Cd(II), and 0.2 μg L⁻¹ for Pb(II) in connection with 120 s deposition step, offering good reproducibility of ±3.8% for Cd(II), and ±1.2% for Pb(II) (30 μg L⁻¹, n = 10). Preliminary experiments disclosed that SbF-CPE and MF-CPE exhibit comparable performance for measuring trace concentration levels of Zn(II) in acidic medium with pH 2, whereas its detection with BiF-CPE was practically impossible. Finally, the practical applicability of SbF-CPE was demonstrated via measuring Cd(II) and Pb(II) in a real water sample.