Unmodified Carbon Paste Electrode Research Articles

A new voltammetric sensor for electrocatalytic determination of vitamin C in fruit juices and fresh vegetable juice using modified multi-wall carbon nanotubes paste electrode

The electrocatalytic oxidation of ascorbic acid (AA) has been studied by p-aminophenol modified carbon nanotubes paste electrode (APMCNTPE). Cyclic voltammetry (CV) and chronoamperometry were used to investigate the suitability of AP as a mediator for the electrocatalytic oxidation of AA in aqueous solution. The oxidation of AA occurs at a potential about 320 mV less positive than with the unmodified carbon paste electrode at pH 7.0. The catalytic reaction rate constant, kh was calculated (2.257 × 103 M−1s−1) using chronoamperometry. The differential pulsevoltammetric (DPV) peak currents of the electrode increased linearly with the corresponding AA concentration in the range of 2.0 × 10−7 M – 1.2 × 10−4 M with a detection limit of 8.0 × 10−8 M. The influence of pH and potential interfering substances on the determination of AA were studied. Finally, the proposed method was also examined as a selective, simple and precise electrochemical sensor for the determination of AA in real samples such as fruit juices and fresh vegetable juice.

Synthesis and characterization of ferrocenecarboxaldehyde immobilized on modified SiO2–Al2O3 in nanoscale, application for determination of penicillamine

In this study, we prepared a stable covalently bonded ferrocene derivative (ferrocenecarboxaldehyde) over SiO2–Al2O3 mixed-oxide in nanoscale size (Fe ions did not accumulate and were dispersed as Fe metal ion–nanoparticles). SiO2–Al2O3 mixed-oxide was functionalized with 3-aminopropyl-triethoxysilane group and ferrocenecarboxaldehyde was covalently linked to the organo-functionalized SiO2–Al2O3 mixed-oxide. Fourier transform infrared spectroscopy, UV–Vis, CHN elemental analysis, inductively coupled plasma optical emission spectroscopy (ICP–OES), scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy, transmission electron microscopy (TEM), and cyclic voltammetry were used to characterize the synthesized materials. Nitrogen sorption measurements of the modified Si/Al mixed-oxide confirm the presence of the ferrocene molecules attached to the modified Si/Al mixed-oxide. The considerable decrease in the specific surface area clearly indicates functionalization of the surface of the mixed-oxide with ferrocene. The nitrogen and Fe contents of the organometallic-modified Si/Al mixed-oxide (SAPFE) were determined by elemental analysis and ICP–OES, respectively, which were then used to compute the immobilized SAPFE content. SEM and TEM images confirm that the metal particle (Fe ions) size distribution forms a continuum between the minimal (2–5 nm) and the maximal (about 50 nm) diameters. The organo-functionalized SiO2–Al2O3 mixed-oxide was used as a mediator for the determination of penicillamine at pH 6.0. Under the optimum conditions at pH 6.0, the oxidation peak potential of penicillamine at the modified electrode shifts about 400 mV to less positive value than for the unmodified carbon paste electrode. Differential pulse voltammetry exhibited two wide linear dynamic ranges of 0.06–7.5 and 7.5–140 μmol L−1 penicillamine. The detection limit was found to be 0.01 μmol L−1 penicillamine. Kinetic parameters such as electron transfer coefficient and catalytic reaction rate constant were also determined using the electrochemical approaches. Finally, the modified electrode was used as a novel nanosensor for the determination of penicillamine in real samples such as drug, serum, and urine.

Selective voltammetric determination of norepinephrine in the presence of acetaminophen and tryptophan on the surface of a modified carbon nanotube paste electrode

A new electrochemical sensor for the determination of norepinephrine (NE), acetaminophen (AC) and tryptophan (TRP) is described. The sensor is based on carbon paste electrode (CPE) modified with 5-mino-3′,4′-dimethyl-biphenyl-2-ol (5ADB) and takes the advantages of carbon nanotubes (CNTs), which makes the modified electrode highly sensitive for the electrochemical detection of these compounds. Under the optimum pH of 7.0, the oxidation of NE occurs at a potential about 170mV less positive than that of the unmodified CPE. Also, square wave voltammetry (SWV) was used for the simultaneous determination of NE, AC and TRP at the modified electrode.

Electrochemical determination of catechol in tea samples using anthraquinone modified carbon paste electrode

Electrochemical investigation of catechol using square wave voltammetry with anthraquinone modified carbon paste electrode was found to be very sensitive. Compared with the unmodified carbon paste electrode, the anthraquinone modified electrode remarkably increases the peak currents of catechol, and greatly lowers the peak potential separation. Two varieties of tea, namely green, and black variety: Wush Wush tea, from Ethiopia, known by its brand name were investigated. Responses for the extracts using ethanol: water (1:4) % v/v showed green tea to be superior in catechol content. Optimization of different variables such as pH of working solution, modifier composition and square wave parameters such as frequency, amplitude and step potential were made to improve the method efficiency during the experiment. The reproducibility for the nine repeated analysis of 80 μmol·L－1 of catechol gave a relative standard deviation of 3.65% and linear calibration plots were obtained in the range 6 to 80 μmol·L－1 with (R = 0.998) and the detection limit with (S/N = 3) was as low as 2.155 x 10－7 mol·L－1.

A new strategy for the selective determination of glutathione in the presence of nicotinamide adenine dinucleotide (NADH) using a novel modified carbon nanotube paste electrode

A novel electrochemical sensor for the simultaneous determination of glutathione (GSH) and nicotinamide adenine dinucleotide (NADH) is described. The sensor is based on a carbon paste electrode (CPE) modified with benzamide derivative and multiwall carbon nanotubes. This mixture makes a modified electrode that is sensitive for the electrochemical detection of these compounds. Under optimum conditions and at pH 7.0, oxidation of GSH occurs at a potential of about 330mV less positive than that at an unmodified CPE. The voltammetric peak currents are linearly dependent on GSH and NADH concentrations in the ranges 0.09–300μmolL−1 GSH and 5.0–600μmolL−1 NADH. The detection limits found for GSH and NADH were 0.05μmolL−1 and 1.0μmolL−1, respectively. The electrochemical sensor was also used for the determination of GSH in urine, pharmaceutical and hemolysed erythrocyte samples.

Ionic liquid/multiwall carbon nanotubes paste electrode for square wave voltammetric determination of methyldopa

Ionic liquid/multiwall carbon nanotubes paste electrode has been used as a novel sensor for the efficient quantitative determination of methyldopa (MDOP) in pharmaceutical and biological samples by using square wave voltammetry. This new sensor shows a better electrochemical response with lower over-potential and high sensitivity for MDOP compared with unmodified carbon paste electrode in physiological condition. The electro-oxidation of MDOP occurred in a pH-dependent 2e− and 2H+ process, and the electrode reaction followed a diffusion-controlled pathway. Under the optimum conditions, the voltammetric oxidation peak current of MDOP showed two linear dynamic ranges with a detection limit of 0.1 μM for MDOP. The novel sensor has been found selective and successfully implemented for the determination of MDOP in real samples such as tablet and patient urine.

Polyvinylpyrrolidone-enhanced electrochemical oxidation and detection of acyclovir

Polyvinylpyrrolidone (PVP), a macromolecule surfactant, was used to modify the carbon paste electrode (CPE). The electrochemical behavior of acyclovir was studied, and a sensitive oxidation peak at 1.03V was observed in pH5 acetate buffer. Compared with the unmodified CPE, the resulting PVP-modified CPE greatly increased the oxidation signal of acyclovir, exhibiting strong surface enhancement effect. The oxidation mechanism of acyclovir was discussed. It was found that the oxidation of acyclovir involved two electrons and two protons. The influences of pH value, amount of PVP, accumulation potential and time were examined on the oxidation signal of acyclovir. As a result, a novel electrochemical method was developed for the detection of acyclovir. The linear range was from 1×10−8 to 7.5×10−7M, and the detection limit was 2.5×10−9M. The proposed method was demonstrated using acyclovir injection and tablets, and the accuracy was tested using high performance liquid chromatography.

Simultaneous determination of captopril, acetaminophen and tryptophan at a modified electrode based on carbon nanotubes

A novel modified carbon paste electrode (CPE) based on a new synthesized compound of (E)-3-((2-(2,4-dinitrophenyl)hydrazono)methyl)benzene-1,2-diol (DHB) and carbon nanotubes (CNTs) was prepared. At first the redox properties of the modified electrode was studied by cyclic voltammetry (CV). Then the modified electrode was used as an electrochemical sensor for oxidation of captopril (CAP). Under the optimum pH of 7.0, the overpotential of CAP oxidation decreases about 500mV at modified electrode than unmodified CPE. Differential pulse voltammetry (DPV) of CAP at the electrochemical sensor exhibited two linear dynamic ranges with a detection limit (3σ) of 70nM. Also DPV was used for selective and simultaneous determination of CAP, acetaminophen (AC) and tryptophan (Trp) by the electrochemical sensor. The proposed electrochemical sensor was used for determination of these substances in real sample.

Graphene-carbon paste electrode for cadmium and lead ion monitoring in a flow-based system

An environment friendly electrode for determining Cd2+ and Pb2+ levels in an automated flow system was successfully developed. Cyclic voltammetry and square wave anodic stripping voltammetry (SWASV) coupled with sequential injection analysis (SIA) were employed to study the electrochemical behavior of the electrode. The in situ bismuth-modified graphene-carbon paste electrode (Bi-GCPE) exhibited excellent electrooxidation of Cd2+ and Pb2+ in the automated flow system with a significantly higher peak current for both metal ions compared with the unmodified CPE. The limits of detection from this method were 0.07 and 0.04μgL−1 for Cd2+ and Pb2+, respectively, with a linear oxidation peak current response for Cd2+ and Pb2+ in the range of 0.10–50.0μgL−1 under optimum conditions. The Bi-GCPE was also applied for the determination of Cd2+ and Pb2+ in low- (tap water) and high- (sea bass fish and undulated surf clam tissues) matrix complexity samples by automated flow system. The recoveries were acceptable and ranged from 70.4% to 120% for Cd2+ and 65.8% to 113.5% for Pb2+.

Electrocatalytic determination of l-cysteine using a modified carbon nanotube paste electrode: Application to the analysis of some real samples

Abstract The electrooxidation of l -cysteine ( l -Cys) was studied using a benzoylferrocene (BF) modified multi-wall carbon nanotube paste electrode (BFCNPE) using cyclic voltammetry (CV), square wave voltammetry (SWV) and chronoamperometry (CHA). Under optimum pH in CV the oxidation of l -Cys occurs at a potential about 215 mV less positive than that at the surface of unmodified carbon paste electrode. The catalytic oxidation peak currents were dependent on the l -Cys concentration and a linear calibration curve was obtained in the range 0.7–350.0 μmol/L of l -Cys with SWV method. The detection limit (3 σ ) was determined as 0.1 μmol/L. This method was also used for the determination of l -Cys in some real samples.

Voltammetric determination of isoproterenol using a 5-amino-2′,4′-dimethoxybiphenyl-2-ol modified carbon nanotube paste electrode

Abstract A new electrochemical sensor for determination of isoproterenol (IP) is described. The sensor is based on carbon paste electrode (CPE) modified with 5-amino-2′,4′-dimethoxybiphenyl-2-ol (5ADMB) and takes the advantages of carbon nanotubes (CNTs). Under the optimum pH of 7.0, the oxidation of IP occurs at a potential about 210 mV less positive than that of the unmodified CPE. The oxidation currents increased linearly with two concentration intervals of IP, one is 0.09 to 20.0 μmol/L and, the other is 20.0 to 400.0 μmol/L. The detection limit (3 σ ) obtained by square wave voltammetry (SWV) was 39.0 nmol/L. The practical application of the modified electrode was demonstrated by determining IP in IP ampoule, urine and human blood serum samples.

Surface enhancement of WO3 nanowires toward the oxidation and electrochemical detection of honokiol in traditional Chinese medicine

WO3 nanowires (nano-WO3) were synthesized using a simple hydrothermal technique, and then used to modify the carbon paste electrode (CPE). The electrochemical behavior of honokiol on the unmodified CPE and nano-WO3 modified CPE was compared. It was found that nano-WO3 remarkably increased the oxidation signal of honokiol. The influences of supporting electrolyte, amount of nano-WO3, accumulation potential and time were studied on the oxidation peak current of honokiol. Based on the strong enhancement effect of nano-WO3, a sensitive, simple and rapid electrochemical method was developed for the detection of honokiol. The linear range was from 3×10−8 to 2.0×10−5M, and the detection limit was as low as 1×10−8M after 2-min accumulation. Finally, it was used to determine honokiol in traditional Chinese medicines, and the recovery was over the range between 96.5% and 98.8%.

Electrochemical Determination of Tyrosine in the Presence of Dopamine and Uric Acid at the Surface of Gold Nanoparticles Modified Carbon Paste Electrode

AbstractA gold nanoparticles modified carbon paste electrode (GN‐CPE) was used as a highly sensitive electrochemical sensor for determination of tyrosine (Tyr), dopamine (DA) and uric acid (UA) in phosphate buffer solution (PBS). The study and measurements were carried out by using cyclic voltammetry (CV), differential pulse voltammetry (DPV) and chronoamperometry methods. In DPV, the GN‐CPE could separate the oxidation peak potentials of DA and UA present in the same solution, though at the unmodified CPE the peak potentials were indistinguishable. The prepared electrode showed voltammetric responses with high sensitivity and selectivity for Tyr, DA and UA in optimal conditions, which makes it very suitable for simultaneous determination of these compounds. The calibration curves for Try, DA and UA were linear for the concentrations of each species. The proposed voltammetric approach was also applied to the determination of Tyr concentration in human serum as a real sample.

An electrochemical sensor for p-aminophenol based on the mesoporous silica modified carbon paste electrode

A mesoporous silica was synthesised and used to modify the surface of carbon paste electrode (CPE). The electrochemical behaviours of p-aminophenol were investigated. Compared to the unmodified CPE, the mesoporous silica-modified CPE obviously lowers the oxidation potential of p-aminophenol, and remarkably increases its oxidation peak current. The effects of pH value, amount of mesoporous silica, accumulation potential and time were examined. As a result, a sensitive, rapid and convenient electroanalytical method was developed for p-aminophenol. The linear range is from 0.025 mg L−1 to 3 mg L−1, and the limit of detection is 0.01 mg L−1 after 2-min accumulation. Finally, the method was successfully used to determine p-aminophenol in water samples.

Electrochemical behavior of a carbon paste electrode modified with 5-amino-3′,4′-dimethyl-biphenyl-2-ol/carbon nanotube and its application for simultaneous determination of isoproterenol, acetaminophen and N-acetylcysteine

In this study, a carbon paste electrode modified with carbon nanotubes and 5-amino-3′,4′-dimethyl-biphenyl-2-ol (5ADB) was used to prepare a novel electrochemical sensor. The objective of this novel electrode modification was to seek new electrochemical performances for the detection of isoproterenol (IP) in the presence of acetaminophen (AC) and N-acetylcysteine (NAC). The peak potentials recorded in a phosphate buffer solution (PBS) of pH 7.0 were 265, 445 and 950mV vs. Ag/AgCl/KCl (3.0M) for IP, AC and NAC, respectively. Under the optimum pH of 7.0, the oxidation of IP occurred at a potential about 215mV less positive than that of the unmodified CPE. The response of catalytic current with IP concentration showed a linear relation in the range from 4.0×10−7 to 9.0×10−4M with a detection limit of 2.0×10−7M.

New voltammetric strategy for determination of dopamine in the presence of high concentrations of acetaminophen, folic acid and N-acetylcysteine

A new electrochemical sensor for the simultaneous determination of dopamine (DA), acetaminophen (AC), folic acid (FA) and N-acetylcysteine (NAC) is described. The sensor is based on carbon-paste electrode (CPE) modified with 5-amino-3′,4′-dimethyl -biphenyl-2-ol (5ADB) and takes the advantages of carbon nanotubes (CNTs), which makes the modified electrode highly sensitive for the electrochemical detection of these compounds. Under the optimum pH of 7.0, the oxidation of DA occurs at a potential about 170mV less positive than that of the unmodified CPE. Also, square wave voltammetry was used for the simultaneous determination of DA, AC, FA and NAC at the modified electrode.

Electrocatalytic oxidation and voltammetric determination of levodopa in the presence of carbidopa at the surface of a nanostructure based electrochemical sensor

In the present paper, the use of a carbon paste electrode modified by meso-tetrakis(3-methylphenyl) cobalt porphyrin (CP) and TiO2 nanoparticles for the determination of levodopa (LD) and carbidopa (CD) was described. Initially, cyclic voltammetry was used to investigate the redox properties of this modified electrode at various scan rates. Next, the mediated oxidation of LD at the modified electrode was described. At the optimum pH of 7.0, the oxidation of LD occurs at a potential about 150mV less positive than that of an unmodified carbon paste electrode. Based on differential pulse voltammetry (DPV), the oxidation of LD exhibited a dynamic range between 0.1 and 100.0μM and a detection limit (3σ) of 69±2nM. DPV was used for simultaneous determination of LD and CD at the modified electrode, and quantitation of LD and CD in some real samples (such as tablets of Parkin-C Fort and Madopar, water, urine, and human blood serum) by the standard addition method.

Electrocatalytic determination of sulfite using a modified carbon nanotubes paste electrode: application for determination of sulfite in real samples

This paper introduces a carbon paste electrode modified with ferrocene and carbon nanotubes as a voltammetric sensor for determination of sulfite at pH 7.0. The results showed that under the optimum condition (pH 7.0) in cyclic voltammetry, the oxidation of sulfite occurred at a potential about 280 mV less positive than the unmodified carbon paste electrode. Kinetic parameters such as electron transfer coefficient (α) and heterogeneous rate constant (k) for sulfite were also determined using electrochemical approaches. Under the optimized conditions, the electrocatalytic oxidation peak current of sulfite showed two linear dynamic ranges with a detection limit of 0.1 μM for sulfite. The proposed method was examined as a selective, simple, and precise method for voltammetric determination of sulfite in some real samples such as weak liquor from wood and paper industry, boiler water, river water, industrial water, and tap water.

Simultaneous determination of dopamine, uric acid, and tryptophan using an MWCNT modified carbon paste electrode by square wave voltammetry

A highly sensitive method was investigated for the simultaneous determination of dopamine (DA), uric acid (UA), and tryptophan (TRP) using a multiwall carbon nanotubes/5-amino-3',4'-dimethoxy-biphenyl-2-ol modified carbon paste electrode (5ADMBCNPE). The 5ADMBCNPE displayed excellent electrochemical catalytic activities towards the oxidation of DA, UA, and TRP. The electrochemical profile of the proposed modified electrode was analyzed by cyclic voltammetry (CV), which showed a shift in the oxidation peak potential of DA at 160 mV to a less positive value compared with an unmodified carbon paste electrode. Square wave voltammetry (SWV) in 0.1 M phosphate buffer solution (PBS) at pH 7.0 was performed to determine DA in the range from 1.2 to 800.0 \mu M, with a detection limit of 0.16 \mu M. The present method was applied to the determination of DA in some real samples.

Electrochemical Behavior and Determination of Rutin on Modified Carbon Paste Electrodes

The performances of ionic liquid (1-hexyl-3-methylimidazolium-bis(trifluoromethylsulfonyl)imide, IL/CPE) and iron phthalocyanine (IP/CPE) modified carbon paste electrodes in electroanalytical determinations of rutin were evaluated and compared to the performance of unmodified carbon paste electrode (CPE). Cyclic voltammetry (CV), differential pulse voltammetry (DPV), differential pulse adsorptive stripping voltammetry (DPAdSV), and amperometry were used for rutin analysis. The best current responses of rutin were obtained at pH 4.0 for all tested techniques. IL/CPE electrode was found to perform best with DPAdSV technique, where a detection limit (LOD) as low as 5 nmol L−1 of rutin was found. On the other hand, IP/CPE showed itself to be an optimum choice for DPV technique, where LOD of 80 nmol L−1 was obtained. Analytical applicability of newly prepared electrodes was demonstrated on determination of rutin in the model samples and the extracts of buckwheat seeds. To find an optimum method for buckwheat seeds extraction, a boiling water extraction (BWE), Soxhlet extraction (SE), pressurized solvent extraction (PSE), and supercritical fluid extraction (SFE) were tested.