Unmodified Carbon Paste Electrode Research Articles

Electrocatalytic oxidation of dopamine on 2,2′-[3,6-dioxa-1,8-octanediylbis(nitriloethylidyne)]-bis-hydroquinone modified carbon paste electrode

A chemically modified carbon paste electrode with 2,2′-[3,6-dioxa-1,8-octanediylbis(nitriloethylidyne)]-bis-hydroquinone (DOH) was employed to study the electrocatalytic oxidation of dopamine (DA) in buffer solution using cyclic voltammetry (CV), square wave voltammetry (SWV) and chronoamperometry (CHA). The diffusion coefficient (D = 7.4 × 10−6 cm2 s−1), and the kinetic parameter such as the electron transfer coefficient (α = 0.33) of DA oxidation at the surface of 2,2′-[3,6-dioxa-1,8-octanediylbis(nitriloethylidyne)]-bis-hydroquinone modified carbon paste electrode (DOHMCPE) was determined using electrochemical approaches. It has been found that under an optimum condition (pH 7.0), the oxidation of DA at the surface of the modified electrode occurs at a potential about 290 mV less positive than that of an unmodified carbon paste electrode. The catalytic oxidation peak currents showed a linear dependence on the DA concentration and linear analytical curves were obtained in the ranges of 3.0 × 10−5 M–2 × 10−3 M of DA with SWV. The detection limits (2σ) were determined to be 3.2 × 10−6 M. This method was also used for the determination of DA in a pharmaceutical preparation (injection) by the standard addition method.

Voltammetric sensor for D-penicillamine determination based on its electrocatalytic oxidation at the surface of ferrocenes modified carbon paste electrodes

Electrocatalytic oxidation of D-penicillamine (D-PA) at the surface of ferrocene modified carbon paste electrode (FCCPE) was thoroughly investigated in aqueous solution with various pH. The performance of this modified electrode was compared with those of 2,7-bis(ferrocenyl ethyl) fluoren-9-one modified carbon paste electrode (2,7-BFEFMCPE). In the optimum condition, the oxidation of d-PA at the surface of FCCPE and 2,7-BFEFMCPE is occurred about 480 and 320 mV less positive than that unmodified carbon paste electrode, respectively. The linear dynamic ranges 6 × 10−5 M-2 × 10−3 M, 6·5 × 10−5 M-1·1 × 10−3 M and 7 × 10−6 M-1·6 × 10−4M, 7 × 10−6 M-2 × 10−4 M of D-PA are obtained from CV and DPV methods for FCCPE and 2,7-BFEFMCPE, respectively. The detection limits (3σ) were determined as 5·4 × 10−5 M and 6·3 × 10−5 M in CV and 6·2 × 10−6 M and 6·8 × 10−6 M in DPV determinations for FCCPE and 2,7-BFEFMCPE, respectively. The proposed method was applied in a highly sensitive determination of d-PA in drug and human synthetic serum samples by standard addition and recovery methods, respectively.

Electrocatalytic activity of 6,7-dihydroxy-3-methyl-9-thia-4,4a-diazafluoren-2-one/multi-wall carbon nanotubes immobilized on carbon paste electrode for NADH oxidation: Application to the trace determination of NADH

Abstract A 6,7-dihydroxy-3-methyl-9-thia-4,4a-diazafluoren-2-one/multi-wall carbon nanotubes (DDF/MWCNT) film-modified carbon paste electrode (CPE) has been fabricated. The electrochemical oxidation of the behavior of reduced nicotinamide adenine dinucleotide (NADH) has been studied at DDF/MWCNT film-modified CPE by electrochemical methods. The DDF/MWCNT film-modified CPE showed a pair of well-defined, quasi-reversible cyclic voltammogram (CV) which corresponds to the transformation of catechol to o-benzoquinone redox couple. With this modified electrode the oxidation potential of the NADH was shifted about 0.333 V toward a less positive value, presenting a peak current much higher than those measured on an unmodified CPE. Detailed analysis of cyclic voltammograms and chronoamperogram gave fundamental electrochemical parameters including the electroactive surface coverage ( Г ), the transfer coefficient ( α ) and the catalytic rate constant ( k ′). Under the selected conditions, two linear calibration curves for NADH were obtained in the concentration ranges of 1–10 nM and 10–80 nM with the detection limit of 0.7 nM. This modified electrode was quite effective to detect the trace amounts of NADH in the presence of the ascorbic acid (AA) or uric acid (UA).

Electrochemical determination of hesperidin using mesoporous SiO2 modified electrode

Mesoporous SiO2 was synthesized and used for modification of the surface of a carbon paste electrode (CPE). In pH 8.0 phosphate buffer, an irreversible oxidation peak at 0.38 V is observed for hesperidin. Compared to the unmodified CPE, the modified CPE remarkably increases the oxidation signal of hesperidin. The effects of pH value, amount of mesoporous SiO2 and accumulation time were examined. As a result, a sensitive and convenient electroanalytical method was developed for hesperidin. Its linear range is from 0.5 to 25 μM, and the limit of detection is 0.25 μM. The method was applied to determine hesperidin in several traditional Chinese medicines.

Surface effects of mesoporous silica modified electrode and application in electrochemical detection of dopamine

Mesoporous silica nanoparticles (meso-SiO 2) were synthesized and used to modify the surface of carbon paste electrode (CPE). The surface properties of CPE and meso-SiO 2/CPE were examined. Compared with the unmodified CPE, meso-SiO 2/CPE remarkably enhances the peak currents of K 3[Fe(CN) 6]. The effective surface areas of CPE and meso-SiO 2/CPE were calculated to be 0.042 cm 2 and 0.208 cm 2, indicating that meso-SiO 2 possesses notable surface enhancement effect. Moreover, the electrochemical behaviors of dopamine (DA) were examined. At the meso-SiO 2/CPE, the oxidation signals of DA greatly increase, and the oxidation potential shifts negatively, suggesting that meso-SiO 2/CPE exhibits catalytic activity to DA. Based on this, a sensitive and simple electrochemical method was developed for the detection of DA. The linear range is from 0.4 μM to 25 μM, and the limit of detection is as low as 0.1 μM.

Selective Detection of Uric Acid in the Presence of Ascorbic Acid and Acetaminophen at a Glassy Carbon Paste Electrode in an Alkaline Solution

Abstract Selective determination of uric acid (UA) was conducted in the presence of ascorbic acid (AA) and acetaminophen (APAP) as interference species at an unmodified glassy carbon paste electrode (GCPE). Using the GCPE prepared in our lab, we succeeded in detecting UA in the presence of AA in acidic and alkaline media. In addition, the oxidation peak potential of APAP is very close to that of UA in neutral media, but in alkaline media, a peak separation of ca. 140 mV was obtained between UA and APAP on the differential pulse voltammogram (DPV).

Electrochemical determination of phenol using CTAB‐functionalized montmorillonite electrode

Montmorillonite calcium (MMT) was modified with cetyltrimethylammonium bromide (CTAB) via replacement of its inorganic exchangeable cations. The resulting CTAB‐modified MMT (CTAB/MMT) was used to modify the carbon paste electrode (CPE). The electrochemical behaviours of phenol at the unmodified CPE, MMT‐modified CPE and CTAB/MMT‐modified CPE were examined. It was found that the oxidation signal of phenol was remarkably improved at the CTAB/MMT‐modified CPE, which was attributed to the higher accumulation efficiency of CTAB/MMT. Based on this, a sensitive and convenient electrochemical method was proposed for the determination of phenol. The effect of supporting electrolyte on the oxidation of phenol was examined, and 0.1 mol l−1 NaOH was finally employed. In addition, the influences of mass content of CTAB/MMT and accumulation time were also investigated. The optimal mass content of CTAB/MMT is 25%, and the accumulation time is 3 min. Under the optimized conditions, the oxidation peak current of phenol is proportional to its concentration over the range from 1.0×10−7 to 3.0×10−5 mol l−1, and the limit of detection is estimated to be 6.0×10−8 mol l−1. Finally, the CTAB/MMT‐modified CPE was successfully applied to determine phenol in water samples.

ELECTROCHEMICAL CHARACTERIZATION OF CARBON PASTE ELECTRODES MODIFIED WITH NATURAL ZEOLITE

A comparative study between carbon paste electrodes (CPE) modified with natural zeolite (ZMCPE, 20 and 50 wt.% clinoptilolite as a major phase) and unmodified CPE (UCPE) is reported. The electro-oxidation of reactive azo-dye (C.I. Reactive Blue 69) was used as a probe to evaluate the performance of these materials. In order to understand the electro-catalytic behavior, cyclic voltammetry (CV), linear sweep voltammetry (LSV), and real time (i-t) techniques were performed. It was found that ZMCPE presents different anodic processes in both free and azo-dye based solutions as a function of zeolite concentration, compared to UCPE. According to the i-E characteristic, in a solution containing azo-dye compound, ZMCPE (50 wt.% oz zeolite) presents major catalytic activity in acid conditions, as revealed by UV-vis spectroscopy. Particle size-shape distribution and structural-textural properties in the zeolite framework and onto the CPE bulk, compared to UCPE electrodes, promote this catalytic effect.

Mesoporous silica-based electrochemical sensor for simultaneous determination of honokiol and magnolol

A kind of mesoporous SiO2 was synthesized using cationic surfactant as the structure-directing template. After that, the resulting mesoporous SiO2 was used to modify the carbon paste electrode (CPE). The electrochemical behaviors of honokiol and magnolol were examined. In pH 6.5 phosphate buffer, two well-shaped oxidation peaks at 0.31 and 0.44 V were observed at the mesoporous SiO2-modified CPE. Compared with the unmodified CPE, the mesoporous SiO2-modified CPE remarkably enhances the oxidation peak currents of honokiol and magnolol. This suggests that mesoporous SiO2 exhibits considerable surface enhancement effects to honokiol and magnolol. After optimizing the parameters such as pH value, amount of mesoporous SiO2, and accumulation time, a sensitive and simple electrochemical method was proposed for the simultaneous determination of honokiol and magnolol. As to honokiol, the calibration curve is from 2.0 to 100.0 µg L−1, and the limit of detection is 0.5 µg L−1 (1.8 × 10−9 mol L−1). For magnolol, the linear range is from 20.0 to 200.0 µg L−1, and the limit of detection is 10.0 µg L−1 (3.8 × 10−8 mol L−1). Finally, the newly proposed method was successfully employed to determine honokiol and magnolol in Chinese traditional medicines.

Electrocatalytic oxidation of ascorbic acid at a 2,2′-(1,8-octanediylbisnitriloethylidine)-bis-hydroquinone modified carbon paste electrode

Cyclic voltammetry and chronoamperometry were used to investigate the electrochemical behavior of ascorbic acid at a carbon paste electrode modified with 2,2′-(1,8-octanediylbisnitriloethylidine)-bis-hydroquinone (1,8-OBNEBHQ). The modified carbon paste electrode showed high electrocatalytic activity toward ascorbic acid; the current was enhanced significantly relative to the situation prevailing when an unmodified carbon paste electrode was used. The electrocatalytic process was highly dependent on the pH of the supporting electrolyte. The apparent charge transfer rate constant, ks, and transfer coefficient, α, for electron transfer between 1,8-OBNEBHQ and carbon paste electrode were calculated as 20.2 ± 0.5 s−1 and 0.47, respectively. Using differential pulse voltammetry, the calibration curves for AA were obtained over the range of 5–30 and 40–1,500 μM, respectively. The detection limit (kσ, k = 2) was 0.6 μM. With good selectivity and sensitivity, the present method provides a simple method for selective detection of ascorbic acid in biological samples.

Ferrocenedicarboxylic acid modified carbon paste electrode: a sensor for electrocatalytic determination of hydrochlorothiazide

The electrocatalytic oxidation of hydrochlorothiazide has been studied by ferrocenedicarboxylic acid modified carbon paste electrode. Cyclic voltammetry and chronoamperometry were used to investigate the suitability of ferrocenedicarboxylic acid as a mediator for the electrocatalytic oxidation of hydrochlorothiazide in aqueous solution. The oxidation of hydrochlorothiazide occurs at a potential about 300 mV less positive than with the unmodified carbon paste electrode at pH 9.0. The catalytic reaction rate constant, kh was calculated (3.38 × 102 cm3 mol-1 s-1) using chronoamperometry.Under the optimized conditions, the electrocatalytic oxidation peak current of hydrochlorothiazide showed two linear dynamic ranges with a detection limit of 0.037 µmol L-1 hydrochlorothiazide. The linear calibration ranges were between 0.08-5.8 µmol L-1 and 5.8-500.0 µmol L-1 hydrochlorothiazide using square wave voltammetric method. Finally, the proposed method was also examined as a selective, simple and precise electrochemicalsensor for the determination of hydrochlorothiazide in real samples such as drug and urine.

Electrochemical Study of Dopamine and Ascorbic Acid by Means of Supramolecular Systems

The present research work presents the results concerning the effect of the modifications done on a carbon paste electrode, CPE, through using supramolecular systems, such as: multiwalled carbon nanotubes, MWCNT, b-cyclodextrin, b-CD, and a new conducting polymer electrochemically formed on the CPE, via polymerization of the b-CD, polyb-CD. Such systems induced increases in the heterogeneous reaction constants k0 and on the ratio jap/jcp, and a decrease in the Ep difference, as compared to the unmodified CPE. Also, the determination of dopamine, DA, was carried out from a commercial pharmaceutical product in the presence of ascorbic acid, AA, with the CPE/poly-b-CD and the CPE/MWCNT/b-CD, because these gave the best analytical parameters for the quantification of DA, giving satisfactory results.

Voltammetric determination of hypoxanthine based on the enhancement effect of mesoporous TiO 2-modified electrode

A mesoporous TiO 2 was synthesized according to the reported method, and then used to modify the carbon paste electrode (CPE). The electrochemical behavior of hypoxanthine was investigated with great detail. Compared with the unmodified CPE, the mesoporous TiO 2-modified CPE greatly enhances the oxidation signal of hypoxanthine. Due to huge surface area, well-defined and special mesopores, the mesoporous TiO 2-modified CPE shows considerable enhancement effect toward hypoxanthine. Based on this, a sensitive, rapid and convenient electrochemical method was developed for the determination of hypoxanthine. The linear range is over the range from 2.0 × 10 −7 to 5.0 × 10 −5 mol L −1, and the limit of detection is estimated to be 5.0 × 10 −8 mol L −1. The relative standard deviation (RSD) for 10 mesoporous TiO 2-modified CPEs is 5.7%. Finally, this sensing method was successfully used to determine hypoxanthine in human blood serum samples.

Sensitive and rapid determination of catechol in tea samples using mesoporous Al-doped silica modified electrode

A mesoporous Al-doped silica (Al/SiO 2) was synthesised according to the published method, and then used to modify the carbon paste electrode (CPE). The electrochemical behaviour of catechol was investigated. Compared with the unmodified CPE, the resulting mesoporous Al/SiO 2 modified CPE remarkably increases the peak currents of catechol, and greatly lowers the peak potential separation. Therefore, the mesoporous Al/SiO 2 exhibits catalytic activity to catechol and significantly improves the determining sensitivity. Based on this, a sensitive, rapid and convenient electrochemical method was proposed for the determination of catechol. The linear range is between 5.0 × 10 −7 and 5.0 × 10 −5 mol L −1 with a correlation coefficient of 0.998. The limit of detection is as low as 1.0 × 10 −7 mol L −1. Finally, this novel method was employed to determine catechol in tea samples, which testified by high-performance liquid chromatography.

<b>Voltammetric determination of l-cysteic acid on a 1-[4-(ferrocenyl-ethynyl)phenyl]-1-ethanone modified carbon paste electrode</b>

The electrochemical behaviour of L-cysteic acid was studied at the surface of 1-[4-(ferrocenyl-ethynyl)phenyl]-1-ethanone modified carbon paste electrode (4FEPEMCPE) in aqueous media using cyclic voltammetry and double step potential chronoamperometry. It has been found, that under optimum condition (pH 7.00) in cyclic voltammetry, the oxidation of L-cysteic acid at the surface of 4FEPEMCPE is occurred at a potential about 220 mV less positive than that an unmodified carbon paste electrode. The kinetic parameters such as electron transfer coefficient, α, and catalytic reaction rate constant, K/h, were also determined using electrochemical approaches. The electrocatalytic oxidation peak current of L-cysteic acid showed a linear dependent on the L-cysteic acid concentration and linear calibration curves were obtained in the ranges of 9 × 10-5 - 6.2 × 10-3 M and 2.0 × 10-7 - 1.17 × 10-5 M of L-cysteic acid concentration with cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods, respectively. The detection limits (3σ) were determined equal to 2.3 × 10-5 M and 8.7 × 10-8 M by CV and DPV methods. This method was also examined as a selective, simple and precise new method for voltammetric determination of L-cysteic acid in serum of patient's blood with migraine disease. KEY WORDS: 1-[4-(Ferrocenyl-ethynyl)phenyl]-1-ethanone, L-Cysteic acid, Electrocatalysis, Cyclic voltammetry, Differential pulse voltammetry, Chronoamperometry  Bull. Chem. Soc. Ethiop. 2008, 22(2), 173-182.

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

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

Carbon Paste Electrode Incorporating 1‐[4‐(Ferrocenyl Ethynyl) Phenyl]‐1‐Ethanone for Electrocatalytic and Voltammetric Determination of Tryptophan

AbstractA carbon paste electrode spiked with 1‐[4‐ferrocenyl ethynyl) phenyl]‐1‐ethanone (4FEPE) was constructed by incorporation of 4FEPE in graphite powder‐paraffin oil matrix. It has been shown by direct current cyclic voltammetry and double step chronoamperometry that this electrode can catalyze the oxidation of tryptophan (Trp) in aqueous buffered solution. It has been found that under optimum condition (pH 7.00), the oxidation of Trp at the surface of such an electrode occurs at a potential about 200 mV less positive than at an unmodified carbon paste electrode. The kinetic parameters such as electron transfer coefficient, α and rate constant for the chemical reaction between Trp and redox sites in 4FEPE modified carbon paste electrode (4FEPEMCPE) were also determined using electrochemical approaches. The electrocatalytic oxidation peak current of Trp showed a linear dependent on the Trp concentrations and linear calibration curves were obtained in the ranges of 6.00×10−6 M–3.35×10−3 M and 8.50×10−7 M–6.34×10−5 M of Trp concentration with cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods, respectively. The detection limits (3σ) were determined as 1.80×10−6 M and 5.60×10−7 M by CV and DPV methods. This method was also examined as a selective, simple and precise new method for voltammetric determination of tryptophan in real sample.

Electrochemical characterization of 2, 2′-[1, 2-ethanediylbis (nitriloethylidyne)]-bis-hydroquinone-carbon nanotube paste electrode and its application to simultaneous voltammetric determination of ascorbic acid and uric acid

The preparation and electrochemical characterization of a carbon nanotube paste electrode modified with 2,2′-[1,2-ethanediylbis (nitriloethylidyne)]-bis-hydroquinone, referred to as EBNBH, was investigated. The EBNBH carbon nanotube paste electrode (EBNBHCNPE) displayed one pair of reversible peaks at E pa = 0.18 V and E pc = 0.115 V vs Ag/AgCl. Half wave potential (E 1/2) and ΔE p were 0.148 and 0.065 V vs Ag/AgCl, respectively. The electrocatalytic oxidation of ascorbic acid (AA) has been studied on EBNBHCNPE, using cyclic voltammetry, differential pulse voltammetry and chronoamperometry techniques. It has been shown that the oxidation of AA occurs at a potential where oxidation is not observed at the unmodified carbon paste electrode. The heterogeneous rate constant for oxidation of AA at the EBNBHCNPE was also determined and found to be about 1.07 × 10−3 cm s−1. The diffusion coefficient of AA was also estimated as 5.66 × 10−6 cm2 s−1 for the experimental conditions, using chronoamperometry. Also, this modified electrode presented the property of electrocatalysing the oxidation of AA and uric acid (UA) at 0.18 and 0.35 V vs Ag/AgCl, respectively. The separations of anodic peak potentials of AA and UA reached 0.17 V. Using differential pulse voltammetry, the calibration curves for AA and UA were obtained over the range of 0.1–800 μM and 20–700 μM, respectively. With good selectivity and sensitivity, the present method provides a simple method for selective detection of AA and UA in biological samples.

Voltammetric sensor for nitrite determination based on its electrocatalytic reduction at the surface of p-duroquinone modified carbon paste electrode

A p-duroquinone (tetramethyl-p-benzoquinone) modified carbon paste electrode (DMCPE) was employed to study the electrocatalytic reduction of nitrite in aqueous solutions using cyclic voltammetry (CV), double potential-step chronoamperometry, and differential pulse voltammetry (DPV). It has found that under an optimum condition (pH 1.00), the reduction of nitrite at the surface of DMCPE occurs at a potential of about 660 mV less negative than that of an unmodified carbon paste electrode (CPE). The catalytic rate constant, k′h, based on Andrieux and Saveant theoretical model was calculated as \(k'_h = 4.56 \times 10^{ - 5} \,cm\,s^{ - 1} \) for scan rate 10 mV s-1. Also, the apparent diffusion coefficient, Dapp, was found as 2.5 × 10–10 and 3.61 × 10–5 cm2 s-1for p-duroquinone in carbon paste matrix and nitrite in aqueous buffered solution, respectively. The values for αnα were estimated to be −0.65 and −0.19 for the reduction of nitrite at the surface of DMCPE and CPE, respectively. The electrocatalytic reduction peak currents showed a linear dependence on the nitrite concentration, and a linear analytical curve was obtained in the ranges of 5.0 × 10–5 M to 8.0 × 10–3 M and 6.0 × 10–6 M to 8.0 × 10–4 M of nitrite concentration with CV and DPV methods, respectively. The detection limits (2σ) were determined as 2.5 × 10–5 M and 4.3 × 10–6 M by CV and DPV methods. This method was also applied as a simple, selective and precise method for determination of nitrite in real samples (the weak liquor from the wood and paper factory of Mazandaran province in Iran) by using a standard addition method.

Poly(ortho‐toluidine) Modified Carbon Paste Electrode: A Sensor for Electrocatalytic Reduction of Nitrite

AbstractThe electrocatalytic reduction of nitrite has been studied by poly(ortho‐toluidine) films modified carbon paste electrode (P‐OT/MCPE). Cyclic voltammetry and chronoamperometry techniques were used to investigate the suitability of poly(ortho‐toluidine) as a mediator for the electrocatalytic nitrite reduction in aqueous solution with various pH. Results showed that pH 0.00 is the most suitable for this purpose. In the optimum pH, the reduction of nitrite occurs at a potential about 600 mV more positive than unmodified carbon paste electrode. The catalytic reaction rate constant, (kh), was calculated 8.68×102 M−1 s−1 by the data of chronoamperometry. The catalytic reduction peak current was linearly dependent on the nitrite concentration and the linearity range obtained was 5.00×10−4 M–1.90×10−2 M. Detection limit has been found to be 3.38×10−4 M (2σ). This method has been successfully employed for quantification of nitrite in real sample.