Differential Pulse Anodic Stripping Voltammetric Simultaneous Determination of Copper(II) and Silver(I) with Bis(2‐hydroxyacetophenone) Butane‐2,3‐dihydrazone Modified Carbon Paste Electrodes

The behavior of a modified carbon paste electrode (CPE) for simultaneous determination of copper(II) and silver(I) by anodic adsorptive stripping voltammetry (ASV) was studied. The electrode was built incorporating the bis(2‐hydroxyacetophenone) butane‐2,3‐dihydrazone (BHAB) as a complexing agent to a Nujol‐graphite base paste. The resulting electrode demonstrated linear responses over the range of Cu(II) and Ag(I) concentrations 0.1–20 and 0.01–2.0 µM respectively. The relative standard deviation (RSD) for the determination of 5.0 µM of both metal ions were 2.9 and 3.1 % for Cu(II) and Ag(I), respectively. The method has been applied to the analysis of copper in wheat and barley seed samples and silver in developed radiological film.     

热对银电极阳极膜光电流测定的影响

利用光电流 ,光热信息和热电流方法研究了热对Ag在 1mol/LNaOH溶液中表面阳极膜光电流的影响 .所用光源为 4 88nm和 5 32nm的激光 .结果表明Ag2 O层具有半导体光电流特性 ,在Ag ,Ag2 O和AgO的转变过程中 ,光照下电极表面的温升不同 .对照循环伏安曲线 ,及光电流和热电流曲线 ,可以证明在电位朝负方向扫描过程中于 0 .37V出现的阳极光电流峰和 0 .1V出现的阴极光电流峰主要是由光照下温度升高引起的热电流所造成的 .光电流和热电流随着光强度的增强而线性增强     

Coal as a New Carbon Paste Electrode Modifier with Sorption Properties

A new type of carbon paste electrode modified with subbituminous and bituminous coal is presented. The operability of the coal carbon paste electrode with respect to the working potential window attainable was tested in various electrolytes. Cyclic voltammetry of the reference redox system [Fe(CN)₆]^3?/4? was performed to evaluate electron transfer kinetics. Open‐circuit sorption of Cd(II), Pb(II), and Cu(II) with subsequent anodic stripping voltammetry was used to pilot coal sorption ability. The coal modified carbon paste electrode was also examined as a support for mercury film deposition and anodic stripping voltammetry of metals.     

Preparation of a clay-modified carbon paste electrode based on 2-thiazoline-2-thiol-hexadecylammonium sorption for the sensitive determination of mercury.

A montmorillonite from Wyoming-USA was used to prepare an organo-clay complex, named 2-thiazoline-2-thiol-hexadecyltrimethylammonium-clay (TZT-HDTA-clay), for the purpose of the selective adsorption of the heavy metals ions and possible use as a chemically modified carbon paste electrode (CMCPE). Adsorption isotherms of Hg2+, Pb2+, Cd2+, Cu2+, and Zn2+ from aqueous solutions as a function of the pH were studied at 298 K. Conditions for quantitative retention and elution were established for each metal by batch and column methods. The organo-clay complex was very selective to Hg(II) in aqueous solution in which other metals and ions were also present. The accumulation voltammetry of Hg(II) was studied at a carbon paste electrode chemically modified with this material. The mercury response was evaluated with respect to the pH, electrode composition, preconcentration time, mercury concentration, "cleaning" solution, possible interferences and other variables. A carbon paste electrode modified by TZT-HDTA-clay showed two peaks: one cathodic peak at about 0.0 V and an anodic peak at 0.25 V, scanning the potential from -0.2 to 0.8 V (0.05 M KNO3 vs. Ag/AgCl). The anodic peak at 0.25 V presents excellent selectivity for Hg(II) ions in the presence of foreign ions. The detection limit was estimated as 0.1 microg L(-1). The precision of determination was satisfactory for the respective concentration level.     

Voltammetric determination of captopril using a novel ferrocene-based polyamide as a mediator and multi-wall carbon nanotubes as a sensor

A modified carbon paste electrode was prepared by incorporating multi-wall carbon nanotubes with a ferrocene-based polyamide (FDADO-IPC). A mixture of fine graphite powder with 10 wt % of multi-wall carbon nanotubes was applied to the preparation of the carbon paste (by dispersing in paraffin) that was finally modified with a ferrocene polyamide complex. The electrocatalytic oxidation of captopril (CAP) was investigated on the surface of the FDADO-IPC multi-wall carbon nanotubes modified carbon paste electrode (FDADO-IPC-MCNTPE) using cyclic voltammetry (CV), differential pulse voltammetry (DPV), chronoamperometry (CHA) and chronocoloumetry (CHC). Using the modified electrode, the kinetics of CAP electrooxidation was considerably enhanced by lowering the anodic overpotential through a catalytic fashion. A linear dynamic range of 0.2–200 μM for CAP was obtained in buffered solutions at pH 7.0. The detection limit was 0.08 μM. Differential pulse voltammetry as a simple, rapid, sensitive, and selective method was developed for the determination of CAP in tablet and human urine without any treatment.     

Facile deposition of [60]fullerene and carbon nanotubes on ITO electrode by electrochemical oxidative polymerization of ethylenedioxythiophene

It was found that [60]fullerene encapsulated in p-sulfonatocalix[8]arene and single-walled carbon nanotubes (SWNTs) solubilized by sodium dodecylsulfate can be readily deposited on the ITO electrode by electrochemical oxidative polymerization of ethylenedioxythiophene (EDOT) without chemical modification of these carbon clusters. The driving force for the deposition is an electrostatic interaction between the anionic complexes and the cationic charges of poly(EDOT) formed in the oxidative polymerization process. The surface morphology was thoroughly characterized by scanning electron micrograph: the [60]fullerene/poly(EDOT) film is covered by nano-particles with 20-100 nm diameters whereas the SWNTs/poly(EDOT) film is covered by nanorods with several microm length and ca. 100 nm diameter. The results indicate that the anionic complexes act as nuclei for the polymer growth in the oxidation polymerization. Interestingly, when these modified ITO electrodes were photoirradiated, the appearance of a photocurrent wave was observed. The action spectra showed that the photoexcited energy of [60]fullerene or SWNTs is efficiently collected by the electroconductive poly(EDOT) film and transferred to the ITO electrode.     

Voltammetric characteristics of diazinon on carbon paste electrode modified with tris(ethylenediamine) cobalt(II) iodide

In this study, cyclic and differential pulse voltammetric methods were used to investigate the electrochemical behavior of diazinon at carbon paste electrode modified with tris(ethylenediamine) cobalt(II) iodide ([Co(en)₃]I₂). Cobalt complex showed an anodic peak at 620 mV (vs. Ag/AgCl, in KNO₃ 0.1 M as supporting electrolyte) at carbon paste modified electrode. In the presence of diazinon, anodic peak intensity increased with increasing concentration of diazinon that confirmed electrocatalytic activity of cobalt complex for oxidation of diazinon (EC’ mechanism). Under optimized conditions, a linear calibration curve for diazinon was obtained in the range from 0.05 to 27 mg/L with detection limit 0.0075 mg/L (3S _b /m). Applications of the modified electrode to the determination of diazinon in different water samples were also tested. The results showed a very good precision (RSD < 0.04%) and very stable voltammetric response towards diazinon.     

Electrocatalytic determination of penicillamine using multiwall carbon nanotubes paste electrode and chlorpromazine as a mediator

In this study, we describe the application of carbon paste electrode modified with multiwall carbon nanotubes as a voltammetric sensor for determination of penicillamine (PA) in the presence of chlorpromazine as a mediator. This modified electrode showed very efficient electrocatalytic activity for the anodic oxidation of PA. The peak current of linear sweep voltammograms of PA increased linearly with it’s concentration in the range of 0.5–500 μM PA. The detection limit for PA was 0.2 μM. The RSDs for 1.0 and 10.0 μM PA were 1.1 and 1.7%, respectively. The proposed sensor was successfully applied for the determination of PA in human urine and tablet.     

Cyclodextrin Host‐Guest Recognition Approach for Simultaneous Quantification and Voltammetric Studies of Levodopa and Carbidopa in Pharmaceutical Products

An electrochemical sensor for simultaneous quantification of Levodopa (L‐dopa) and Carbidopa (C‐dopa) using a β‐cyclodextrin/poly(N‐acetylaniline) (β‐CD/PNAANI) modified carbon paste electrode has been developed. Preconcentrating effect of β‐CD as well as its different inclusion complex stability with L‐dopa and C‐dopa was used to construct an electrochemical sensor for quantification of these important analytes. The overlapping anodic peaks of L‐dopa and C‐dopa at 810 mV on bare carbon paste electrode resolved in two well‐defined voltammetric peaks at 450 and 880 mV vs. Ag/AgCl, respectively, with a drastic enhancement of the anodic peak currents. Under optimized conditions, linear calibration curves were obtained in the ranges of 0.5–117 µM and 1.6–210 µM with detection limits down to 0.2 and 0.8 µM for L‐dopa and C‐dopa, respectively. The proposed electrode was successfully applied for the determination of L‐dopa /C‐dopa in pharmaceutical formulations and the results were in close agreement with the labeled values.     

Studies on the voltammetric behaviour of a 2-mercaptoimidazole containing carbon paste electrode: determination of traces of silver

The voltammetric behaviour of a 2-mercaptoimidazole (2-MI) containing carbon paste electrode was studied. When mixed to carbon paste as an electrode modifier, 2-MI can be reduced at negative potentials (–1 V vs. SCE), but it does not give a response in the potential range where Ag(0) is oxidized to Ag(I). Silver could be accumulated from 0.1 mol l^–1 acetate buffer onto a 2-MI modified carbon paste electrode without a potential applied; after medium exchange, it was reduced at –1 V vs. SCE in 0.1 mol l^–1 acetate buffer solution and determined by differential pulse anodic stripping voltammetry. With suitable preconcentration times, the detection limit was 0.1 g l^–1; a linear relation between current and concentration was found to exist within a range of 0.5 to 1000 g l^–1. In the presence of EDTA, common metal ions have no or only little effect on the voltammetric determination of silver.     

Preconcentration and determination of mercury(II) at a chemically modified electrode containing 3-(2-thioimidazolyl)propyl silica gel.

A mercury-sensitive chemically modified graphite paste electrode was constructed by incorporating modified silica gel into a conventional graphite paste electrode. The functional group attached to the (3-chloropropyl) silica gel surface was 2-mercaptoimidazole, giving a new product denoted by 3-(2-thioimidazolyl)propyl silica gel, which is able to complex mercury ions. Mercury was chemically adsorbed on the modified graphite paste electrode containing 3-(2-thioimidazolyl)propyl silica (TIPSG GPE) by immersion in a Hg(II) solution, and the resultant surface was characterized by cyclic and differential pulse anodic stripping voltammetry. One cathodic peak at 0.1 V and other anodic peak at 0.34 V were observed on scanning the potential from -0.1 to 0.8 V (0.01 M KNO3; v = 2.0 mV s(-1) vs. Ag/AgCl). The anodic peak at 0.34 V show an excellent sensitivity for Hg(II) ions in the presence of several foreign ions. A calibration graph covering the concentration range from 0.02 to 2 mg L(-1) was obtained. The detection limit was estimated to be 5 microg L(-1). The precision for six determinations of 0.05 and 0.26 mg L(-1) Hg(II) was 3.0 and 2.5% (relative standard deviation), respectively. The method can be used to determine the concentration of mercury(II) in natural waters contaminated by this metal.     

Electrochemical determination of acetaminophen in the presence of propranolol using an electrode modified with a Schiff base from 2-hydroxy-1-naphthaldehyde and ethylenediamine and multi-walled carbon nanotubes

A carbon paste electrode, modified with N,N′-bis-(2-hydroxy-1-naphthalidene)ethylenediamine and multi-walled carbon nanotubes (HNED-MWCNPE), was used for the determination of acetaminophen (ACOP) and propranolol (PP). Cyclic voltammetry (CV), chronocoulometry, chronoamperometry and differential pulse voltammetry (DPV) techniques were employed to study electro-oxidation of ACOP. The results revealed that the modified electrode showed an electrocatalytic activity toward the anodic oxidation of acetaminophen by a marked enhancement in the current response in buffered solution at pH 8.0. Some kinetic parameters such as the electron transfer coefficient (α) were also determined for the ACOP oxidation. The linear concentration range of 1 × 10^?3?1 × 10^?6 M with a detection limit of 4.6 × 10^?8 M (n = 16) for ACOP was obtained using DPV (pH 8.0). The modified electrode shows good sensitivity, selectivity and stability. The prepared electrode was also applied for the determination of ACOP in human blood serum.     

Anodic stripping voltammetry of silver(I) using a carbon paste electrode modified with multi-walled carbon nanotubes

We describe a silver(I)-selective carbon paste electrode modified with multi-walled carbon nanotubes and a silver-chelating Schiff base, and its electrochemical response to Ag(I). Effects of reduction potential and time, accumulation time, pH of the solution and the stripping medium were studied by differential pulse anodic stripping voltammetry and optimized. The findings resulted in a method for the determination of silver over a linear response range (from 0.5 to 235 ng?mL^?1) and with a detection limit as low as 0.08 ng?mL^?1. The sensor displays good repeatability (with the RSD of ±?2.75 % for 7 replicates) and was applied to the determination of Ag(I) in water samples and X-ray photographic films.

Photochemical and photoelectrochemical behaviour of chlorophyll a-smectite conjugate

Chlorophyll a was adsorbed onto smectite to form chlorophyll-smectite conjugate, which became photostable against light illumination. The chlorophyll-smectite conjugate caused the photoreduction of nitro blue tetrazolium, NBT, through the formation of superoxide anion, and the conjugate retained the photosensitive activity even after 20 hour illumination. Furthermore, the conjugate deposited on SnO₂ electrode caused electron transfer under light illumination. The anodic photocurrent rose at ?200 mV versus Ag/AgCl electrode (KCl saturated) and reached a maximum level at approximately +100 mV. The photocurrent spectrum was in good agreement with the absorption spectrum of chlorophyll-smectite conjugate in an aqueous solution and the quantum efficiency was approximately 1% at 670 nm.     

Simple and low-cost electrochemical sensor based on nickel nanoparticles for the determination of cabergoline

Cabergoline (CAB) is an ergot alkaloid derivative with dopamine agonist activity. In this work for the first time the electrocatalytic oxidation of CAB was carried out with nickel nanoparticles-modified carbon paste electrode using cyclic voltammetry, chronoamperometry, chronocoulometry and amperometry methods. At first, nickel nanoparticles were synthesized by non-aqueous polyol method and these nanoparticles were mixed with graphite powder to form modified carbon paste electrode. The resulting modified electrode was characterized by scanning electron microscope images. In the presence of 0.1 M NaOH a good redox behavior of the Ni(III)/Ni(II) couple at the surface of the electrode can be observed. CAB was successfully oxidized at the surface of the modified electrode. The electrocatalytic oxidation peak current of this drug was linearly dependent on its concentration. The proposed sensor exhibited a high sensitivity and was successfully applied for the determination of CAB in real samples.     

Use of adsorptive square-wave anodic stripping voltammetry at carbon paste electrode for the determination of amlodipine besylate in pharmaceutical preparations

The antihypertensive drug amlodipine has been characterized voltammetrically in a carbon paste electrode by means of anodic stripping voltammetry. An adsorptive stripping method in a carbon paste electrode for trace determination of amlodipine has been described. Cyclic voltammetric studies indicated the oxidation of amlodipine besylate at the electrode surface through a single two-electron irreversible step fundamentally controlled by adsorption. A study of the variation in the peak current with solution variables such as pH, ionic strength, concentration of amlodipine, possible interference, and instrumental variables, such as preconcentration time and accumulation potential, has resulted in the optimization of the oxidation signal for analytical purposes. By anodic adsorptive anodic stripping voltammetry, the calibration plot was linear in the range 9.9 × 10^?9 ? 1.4 × 10^?7 M with a detection limit of 2 × 10^?10 M in a carbon paste electrode at pH 11.0. The procedure was successfully applied to the assay of amlodipine besylate in some commercial products in the market (Amlopres®, Amlodipine, and Norvasc®). The percentage recoveries were in agreement with those obtained by the reference method.     

Self-assembly and characterization of a novel hydrogen-bonded nanostructure

A novel hydrogen-bonded supramolecular system of a [60]fullerene derivative with perylene bisimide was synthesized and characterized. 1H NMR spectra confirmed the existence of strong hydrogen-bonding interaction between compounds 1 and 5. Transmission electron microscopy images of 1.5 aggregates showed spherical particles having a mean diameter of 50 nm. The photocurrent response of the film was measured, and a steady and rapid anodic photocurrent response was obtained.     

Electrochemical Determination of Dopamine Using a Carboxyl-functionalized Carbon Nanotube-Modified Carbon Paste Electrode Doped with Polymeric Ferric Sulfate

A novel electrochemical device for the sensitive determination of dopamine was developed based on a carbon paste electrode with polymeric ferric sulfate doped in the carbon paste and a carboxyl-functionalized carbon nanotube thin film on the surface. The modified electrode was characterized by scanning electron microscopy, electrochemical impedance spectroscopy, and cyclic voltammetry. The conditions for the preparation of electrode were optimized. The carbon nanotubes were shown to be stable on the surface of carbon paste electrode. The novel electrochemical device provided excellent activity toward dopamine. Amperometry and differential pulse voltammetry were used for the determination of dopamine in pH 7.0 phosphate buffer with a long linear range from 0.8 to 261?µM and a detection limit of 0.2?µM. The modified electrode showed excellent repeatability, good stability, and satisfactory reproducibility, thus demonstrating potential for practical applications.     

Efficient charge injection from the S2 photoexcited state of special-pair mimic porphyrin assemblies anchored on a titanium-modified ITO anode

A novel surface fabrication methodology has been accomplished, aimed at efficient anodic photocurrent generation by a photoexcited porphyrin on an ITO (indium-tin oxide) electrode. The ITO electrode was submitted to a surface sol-gel process with titanium n-butoxide in order to deposit a titanium monolayer. Subsequently, porphyrins were assembled as monolayers on the titanium-treated ITO surface via phosphonate, isophthalate, and thiolate groups. Slipped-cofacial porphyrin dimers, the so-called artificial special pair at the photoreaction center, were organized through imidazolyl-to-zinc complementary coordination of imidazolylporphyrinatozinc(II) units, which were covalently immobilized by ring-closing olefin metathesis of allyl side chains. The modified surfaces were analyzed by means of X-ray photoelectron spectroscopy. Photoirradiation of the porphyrin dimer generated a large anodic photocurrent in aqueous electrolyte solution containing hydroquinone as an electron sacrificer, due to the small reorganization energy of the dimer. The use of different linker groups led to significant differences in the efficiencies of anodic photocurrent generation. The apparent flat-band potentials evaluated from the photocurrent properties at various pH values and under biased conditions imply that the band structure of the ITO electrode is modified by the anchoring species. The quantum yield for the anodic photocurrent generation by photoexcitation at the Soret band is increased to 15 %, a surprisingly high value without a redox cascade structure on the ITO electrode surface, while excitation at the Q band is not so significant. Extensive exploration of the photocurrent properties has revealed that hot injection of the photoexcited electron from the S2 level into the conduction band of the ITO electrode takes place before internal conversion to the S1* state, through the strong electronic communication of the phosphonyl anchor with the sol-gel-modified ITO surface.     

Modified Graphite Paste Electrode with Lewatit FO36 Nanoresin/Multi-Walled Carbon Nanotubes for Determination of Quercetin

In the present study, the electrochemical oxidation of quercetin (QUR) was investigated using a graphite paste electrode (GPE) modified with multi-walled carbon nanotube and Lewatit FO36 nanoresin (LFONR-MWCNT/GPE). LFONR-MWCNT/GPE could effectively a sensitive anodic peak at around 0.23 V (vs. SCE) in a 0.10 M phosphate buffer solution. Modified electrode revealed that activated with multiwalled carbon nanotube and LFONR was capable of facilitating electron transfer and increasing surface area. The electrochemical oxidation of QUR was studied using cyclic voltammetry (CV) and linear sweep voltammetry (LSV). Some kinetic parameters for electrochemical oxidation of QUR including total number of electrons (n) and standard heterogeneous rate constant (k_s) were also determined. The calibration graph consisted of two linear segments of 1.8–25.0 μM, and 25.0–570.0 μM with a detection limit of 0.213 μM (based on 3S_b). The applicability of the method to juice of peach, red grape, sour cherry and Gincora tablets analysis was also evaluated.