Electrochemical behavior and detection of guanine using a sodium montmorillonite-modified carbon paste electrode

Herein, a sodium montmorillonite-modified carbon paste electrode is described for the electrochemical determination of guanine. Guanine yields a well-defined and very sensitive oxidation peak at the sodium montmorillonite-modified carbon paste electrode. Compared with the unmodified carbon paste electrode, the modified electrode facilitates the electron transfer of guanine, since it notably increases the oxidation peak current and lowers the oxidation overpotential of guanine. Based on this, a simple sensitive reliable electrochemical method is proposed for the detection of guanine after all the experimental parameters, such as solution pH value, sodium montmorillonite content in the carbon paste electrode, accumulation potential, and time, are optimized. Under the optimized conditions, the oxidation peak current of guanine varies linearly with its concentration in the range 5.0×10⁻⁸ to 2.0×10⁻⁵ M and the detection limit (signal-to-noise=3) is 2.0×10⁻⁸ M after 4-min accumulation. This method is successfully demonstrated with urine samples. Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 2, pp. 178–182. The text was submitted by the authors in English.     

Electrochemical Determination of 10-Hydroxycamptothecin Using a Multi-Wall Carbon Nanotube-Modified Electrode

We report a sensitive and convenient voltammetric method for the direct determination of 10-hydroxycamptothecin (HCPT). At a multi-wall carbon nanotube (MWNT)-modified electrode, HCPT yields a very sensitive and well-shaped oxidation peak, which can be used as analytical signal for HCPT determination. Compared with the poor electrochemical signal at the unmodified GCE, the electrochemical response of HCPT at the MWNT-modified GCE was greatly improved, as confirmed by the significant peak current enhancement. This result indicates that the MWNT-modified GCE has great potential in the sensitive determination of HCPT. Based on this, a very sensitive and simple electrochemical method was proposed for HCPT determination after all the experimental parameters were optimized. The newly-proposed method possesses very low detection limit (2 × 10⁻⁹ mol L⁻¹) and wider linear range (from 1 × 10⁻⁸ to 4 × 10⁻⁶ mol L⁻¹). Rapid and simple sample analysis is another advantage. Finally, this method was successfully demonstrated using HCPT drugs.     

Electrochemical behavior of phenol at acetylene black-dihexadecyl hydrogen phosphate composite modified glassy carbon electrode in the presence of cetyltrimethylammonium bromide

The electrochemical response of phenol at acetylene black (AB)-dihexadecyl hydrogen phosphate (DHP) composite modified glassy carbon electrode in the presence of cetyltrimethylammonium bromide (CTAB) was investigated. In this system, a sensitive oxidation peak at 0.62 V (SCE) was obtained. The electrode process and the influence of CTAB on the oxidation of phenol were explored by chronocoulometry and linear sweep voltammetry (LSV). Experimental conditions for the determination of phenol were optimized. In the range of 5.0 × 10⁻⁷ to 1.2 × 10⁻⁵ M, the phenol concentration was linear with the oxidation peak current and the detection limit was found to be 1.0 × 10⁻⁷ M for 3 min accumulation. The method was applied for the determination of phenol in lake water and the results were satisfactory. Published in Russian in Elektrokhimiya, 2008, Vol. 44, No. 2, pp. 222–229. The text was submitted by the authors in English.     

Electrochemical oxidation behavior of 2,4-dinitrophenol at hydroxylapatite film-modified glassy carbon electrode and its determination in water samples

Hydroxylapatite (HAP)-modified glassy carbon electrode (GCE) was fabricated and used to investigate the electrochemical oxidation behavior of 2,4-dinitrophenol (2,4-DNP) by cyclic voltammetry, differential pulse voltammetry, and chronocoulometry. The oxidation peak current of 2,4-DNP at the modified electrode was obviously increased compared with the bare GCE, indicating that HAP exhibits a remarkable enhancement effect on the electrochemical oxidation of 2,4-DNP. Based on this, a sensitive and simple electrochemical method was proposed for the determination of 2,4-DNP. The effects of HAP concentration, accumulation time, accumulation potential, pH, and scan rate were examined. Under optimal conditions, the oxidation peak current of 2,4-DNP was proportional to its concentration in the range from 2.0 × 10⁻⁶ to 6.0 × 10⁻⁴ M with a correlation coefficient of 0.9987. The detection limit was 7.5 × 10⁻⁷ M (S/N = 3). The proposed method was further applied to determine 2,4-DNP in water samples with recoveries from 96.75% to 106.50%.     

Electrochemical behavior and determination of L-tryptophan on carbon ionic liquid electrode

A carbon ionic liquid electrode (CILE) was fabricated by mixing N-butylpyridinium hexafluoro-phosphate (BPPF ₆ ) with graphite powder and further used for the investigation on the electrochemical behavior of L-tryptophan (Trp). The fabricated CILE showed good conductivity, inherent electrocatalytic ability and strong promotion to the electron transfer of Trp. On the CILE, an irreversible oxidation peak appeared at 0.948 V (vs. saturated calomel reference electrode). For 5.0 × 10⁻⁵ M Trp the oxidation peak current increased about 5 times and the oxidation peak potential decreased on 0.092 V compared to carbon paste electrode. The results indicated that an electrocatalytic reaction occurred on CILE. The conditions for the electrochemical detection were optimized and the electrochemical parameters of Trp on CILE were carefully investigated. Under the selected conditions, the oxidation peak current showed linear relationship with Trp concentration in the range of 8.0 × 10⁻⁶ ∼1.0 × 10⁻³ M for cyclic voltammetry and the detection limit was estimated as 4.8 × 10⁻⁶ M (3σ). The interferences of other amino acids or metal ions on the determination were tested and the proposed method was successfully applied to the synthetic sample analysis.     

Fast and sensitive determination of captopril by voltammetric method using ferrocenedicarboxylic acid modified carbon paste electrode

A ferrocenedicarboxylic acid modified carbon paste electrode was constructed and used as a fast and sensitive tool for the determination of captopril at trace level. It has been shown by direct current cyclic voltammetry and double step chronoamperometry that ferrocenedicarboxylic acid can catalyze the oxidation of captopril in aqueous buffer solution and produces a sharp oxidation peak current at about +0.49 vs. Ag/AgCl reference electrode. The square wave voltammetric peak currents of the electrode increased linearly with the corresponding captopril concentration in the range of 3.0 × 10⁻⁷–1.4 × 10⁻⁴M with a detection limit of 9.1 × 10⁻⁸ M. The influence of pH and potential interfering substances on the determination of captopril were studied. Electrochemical impedance spectroscopy was used to study the charge transfer properties at the electrode–solution interface. Finally, the sensor was examined as a selective, simple, and precise new electrochemical sensor for the determination of captopril in real samples, such as drug and urine, with satisfactory results.     

Multi-walled carbon nanotube paste electrode for selective voltammetric detection of isoniazid

A multi-walled carbon nanotube paste electrode (MWCPE) is prepared as an electrochemical sensor with high sensitivity and selectivity in responding to isoniazid. The electrochemical oxidation of isoniazid is investigated in buffered solution by cyclic and differential pulse voltammetry. The electrode is shown to be very effective for the detection of isoniazid in the presence of other biological reductant compounds. The electrochemical oxidation of cysteine, due to the high overvoltage, is completely stopped at the surface of MWCPE. The electrode exhibits a very good resolution between the voltammetric peak of isoniazid and the peaks of ascorbic acid (AA) and dopamine (DA). A resolution of more than 450 mV between the anodic peak potentials makes the MWCPE suitable for simultaneous detection of isoniazid in the presence of AA or DA in clinical and pharmaceutical preparations. Differential pulse voltammetry (DPV) is applied as a sensitive method for the determination of isoniazid. The linear range in these determinations is 1 × 10⁻⁶–1 × 10⁻³ M for isoniazid and the detection limit is 5 × 10⁻⁷ M. The electrode was applied to the simultaneous determinations in isoniazid and AA mixtures and also, isoniazid and DA mixture over a wide concentration range. The slope variation for the calibration curves of isoniazid (RSD) was less than 4.5% (based on ten measurements over a period of three months).     

Direct electrochemistry and electrocatalysis of nitrite based on nano-alumina-modified electrode

Simple and sensitive electrochemical method for the determination of nitrite, based on a nano-alumina-modified glassy carbon electrode (GCE), is described. Nitrite yields a well-defined oxidation peak whose potential is 0.74 V at the nano-alumina-coated GCE in 0.1 mol L⁻¹ phosphate buffer (pH 5.0). Compared with bare GCE, the nano-alumina-modified GCE has evident catalytic effect towards the oxidation of nitrite, and its peak current can be significantly enhanced. Some of the experimental parameters were optimized for the determination of nitrite. The oxidation peak current was proportional to nitrite concentration in the range of 5.0 × 10⁻⁸–1.1 × 10⁻³ mol L⁻¹, and a detection limit of 1.0 × 10⁻⁸ mol L⁻¹ was obtained. This method has been successfully used to the determination of nitrite in sausage sample. Furthermore, results obtained by the method have been compared with spectrophotometric method.     

Multi-walled carbon nanotubes modified glass carbon electrode and its electrocatalytic activity towards oxidation of paracetamol

Multi-walled carbon nanotubes (MWNTs) modified glassy carbon electrode (GCE) was simply and conveniently fabricated. The electrochemical properties of paracetamol (PCT) at the prepared modified electrode were investigated by cyclic voltammetry (CV). Based on this, an ultrasensitive and rapid electrochemical method was developed for the determination of PCT. The result indicated that the oxidation of PCT was greatly improved at the MWNTs-modified GC (MWNTs/GC) electrode as compared with the bare GC electrode, with relatively high sensitivity, stability and life time. Good linear relationship between the oxidation peak current and the PCT concentration in the range of 1 × 10⁻⁷ to 1 × 10⁻³ M (r = 0.996) was obtained in phosphate buffer solution (PBS) with pH 6.5, the detection limit was 2 × 10⁻⁸ M (S/N = 3) by use of modified electrode. The proposed method was successfully applied to the PCT determination in tablets.     

New adsorptive square wave method for trace determination of prilocain in the flow injection system by a fast fourier analysis

The determination of prilocain, used to manage tonic-clonic seizures, has been carried out at micro gold electrode (Au UME) using continuous fast Fourier transform square wave voltammetry. The Au UME electrode exhibited an effective response towards prilocaine adsorption. The peak current was also found to be significantly increased. The determination was carried out in phosphate containing electrolyte in the pH of 2.0 and a well-defined change on the peak current were noticed. The peak current was found to be linearly dependent on concentration of prilocain in the concentration range 5.0 × 10⁻⁷–1.0 × 10⁻¹¹ M with a detection limit of 5.0 × 10⁻¹² M. This paper describes development of a new analysis system to determine of prilocain by a novel square wave voltammetry method to perform a very sensitive method. The method used for determination of prilocain by measuring the changes in admittance voltammogram of a gold ultramicroelectrode (in 0.05 M H₃PO₄ solution) caused by adsorption of the prilocain on the electrode surface. Variation of admittance in the detection process is created by inhibition of oxidation reaction of the electrode surface, by adsorbed of prilocain. Furthermore, signal-to-noise ratio has significantly increased by application of discrete Fast Fourier Transform (FFT) method, background subtraction and two-dimensional integration of the electrode response over a selected potential range and time window. Also in this work some parameters such as SW frequency, eluent pH, and accumulation time were optimized. The relative standard deviation at concentration 5.0 × 10⁻⁸ M is 5.8% for 5 reported measurements.     

Covalent Modification of Glassy Carbon Electrode with L-Cysteine for the Determination of Acetaminophen

A novel L-cysteine film modified electrode has been fabricated by means of an electrochemical oxidation procedure, and it was successfully applied to the electrochemical determination of acetaminophen. This method utilizes the electrooxidation of amines to their analogous cation radicals to form a chemically stable covalent linkage between the nitrogen atom of the amine and edge plane sites at the glassy carbon electrode surface. The electrochemical behaviour of acetaminophen at the film electrode was investigated in 0.1 mol L⁻¹ phosphate buffer (pH 6.20). It was found that the redox peak current of acetaminophen was enhanced greatly on the film electrode. Linearity between the oxidation peak current and the acetaminophen concentration was obtained in the range of 1.0 × 10⁻⁴–2.0 × 10⁻⁷ mol L⁻¹ with a detection limit of 5.0 × 10⁻⁸ mol L⁻¹. For seven parallel detections of 1.0 × 10⁻⁵ mol L⁻¹ acetaminophen, the relative standard deviation (RSD) was 1.46%, suggesting that the film electrode has excellent reproducibility. Application to the determination of acetaminophen in drug tablets and human urine demonstrated that the film electrode has good stability and high sensitivity.     

Electrochemical oxidation behavior of bisphenol A at surfactant/layered double hydroxide modified glassy carbon electrode and its determination

Electrochemical behavior of bisphenol A (BPA) at glassy carbon electrode-modified with layered double hydroxide (LDH) and anionic surfactant (sodium dodecyl sulfate) is investigated by electrochemical techniques. Compared with the bare electrode and LDH-modified electrode, the oxidation peak potential of BPA shifted negatively and the peak current increased significantly due to the enhanced accumulation of BPA via electrostatic interaction with LDH at the hydrophobic electrode surface. Some determination conditions such as LDH loading, pH, scan rate, accumulation potential, and accumulation time on the oxidation of BPA were optimized. And some kinetic parameters were investigated. Under the optimized conditions, the oxidation current was proportional to BPA concentration in the range of 8 × 10⁻⁹ to 2.808 × 10⁻⁶ M with the detection limit of 2.0 × 10⁻⁹ M by amperometry. The fabricated electrode showed good reproducibility, stability, and anti-interference. The proposed method was successfully applied to determine BPA in water samples, and the results were satisfactory.     

Electrochemical behavior and determination of epinephrine at a mercaptoacetic acid self-assembled gold electrode

The electrochemical behavior of epinephrine (EP) at a mercaptoacetic acid (MAA) self-assembled monolayer modified gold electrode was studied. The MAA/Au electrode is demonstrated to promote the electrochemical response of epinephrine by cyclic voltammetry. The possible reaction mechanism is also discussed. The diffusion coefficient D of EP is 6.85 × 10⁻⁶ cm² s⁻¹. In 0.1 mol L⁻¹ phosphate buffer (pH 7.20), a sensitive oxidation peak was observed at 0.177 V, and the peak current is proportional to the concentration of EP in the range of 1.0 × 10⁻⁵–2.0 × 10⁻⁴ mol L⁻¹ and 1.0 × 10⁻⁷–1.0 × 10⁻⁶ mol L⁻¹. The detection limit is 5 × 10⁻⁸ mol L⁻¹. The modified electrode is highly stable and can be applied to the determination of EP in practical injection samples. The method is simple, quick, sensitive and accurate.     

Electrochemical behaviors of ofloxacin and its voltammetric determination at carbon nanotubes film modified electrode

A multi-wall carbon nanotubes (MWNTs)-Nafion film-coated glassy carbon electrode (GCE) was fabricated and the electrochemical behavior of ofloxacin on the MWNTs-Nafion film-coated GCE were investigated by cyclic voltammetry (CV), linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS). The oxidation peak current of ofloxacin increased significantly on the MWNTs-Nafion film modified GCE compared with that using a bare GCE. This nano-structured film electrode exhibited excellent enhancement effects on the electrochemical oxidation of ofloxacin. A well-defined oxidation peak attributed to ofloxacin was observed at 0.97 V and was applied to the determination of ofloxacin. The oxidation peak current was proportional to ofloxacin concentration in the ranges 1.0 × 10⁻⁸ to 1.0 × 10⁻⁶ mol/L and 1.0 × 10⁻⁶ to 2.0 × 10⁻⁵ mol/L. A detection limit of 8.0 × 10⁻⁹ mol/L was obtained for 400 s accumulation at open circuit (S/N = 3). This method for the detection of ofloxacin in human urine was satisfactory. __________ Translated from Chinese Journal of Applied Chemistry, 2007, 24(5): 540–545 [译自: 应用化学]     

Electrochemical oxidation of salicylic acid at well-aligned multiwalled carbon nanotube electrode and its detection

In this paper, an electrochemical sensor for sensitive and convenient determination of salicylic acid (SA) was constructed using well-aligned multiwalled carbon nanotubes as electrode material. Compared to the glassy carbon electrode, the electro-oxidation of SA significantly enhanced at the multiwalled carbon nanotube (MWCNT) electrode. The MWCNT electrode shows a sensitivity of 59.25 μA mM⁻¹, a low detection limit of 0.8 × 10⁻⁶ M and a good response linear range with SA concentration from 2.0 × 10⁻⁶ to 3.0 × 10⁻³ M. In addition, acetylsalicylic acid was determined indirectly after hydrolysis to SA and acetic acid, which simplified the detection process. The mechanism of electrochemical oxidation of SA at the MWCNT electrode is also discussed.     

Electrochemical determination of ascorbic acid using the poly-cysteine film-modified electrode

A poly(L-cysteine) thin film was prepared onto electrode surface via electropolymerization. In pH 7.0 phosphate buffer, L-cysteine was oxidized during the cyclic potential sweep between −0.60 and 2.00 V, forming a thin film at the glassy carbon electrode (GCE) surface. The electrochemical behaviors of ascorbic acid at the bare GCE and the poly(L-cysteine) film-coated GCE were investigated. The oxidation peak potential of ascorbic acid shifts to more negative potential at the poly(L-cysteine) film-modified GCE. Moreover, the oxidation peak current significantly increases at the poly(L-cysteine) film-modified GCE. These phenomena indicate that poly(L-cysteine) film shows highly-efficient catalytic activity to the oxidation of ascorbic acid. Based on this, a sensitive and simple electrochemical method was proposed for the determination of ascorbic acid. The oxidation peak current of ascorbic acid is proportional to its concentration over the range from 1.0 × 10⁻⁶ to 5.0 × 10⁻⁴ mol l⁻¹. The limit of detection is evaluated to be 4.0 × 10⁻⁷ mol l⁻¹.     

Electrochemical determination of acetaminophen using a glassy carbon electrode coated with a single-wall carbon nanotube-dicetyl phosphate film

Single-wall carbon nanotubes (SWNT) were dispersed into water in the presence of dicetyl phosphate (DCP), and then a SWNT-DCP film-coated glassy carbon electrode (GCE) was constructed. The electrochemical behavior of acetaminophen at bare GCE and SWNT-DCP modified GCE were compared, suggesting that the SWNT-DCP-modified GCE significantly enhances the oxidation peak current of acetaminophen. A sensitive and simple electrochemical method with a good linear relationship in the range of 1.0 × 10⁻⁷–2.0 × 10⁻⁵ mol L⁻¹, was developed for the determination of acetaminophen. The detection limit is 4.0 × 10⁻⁸ mol L⁻¹ for 3-min accumulation. This method was successfully demonstrated with tablets.     

Voltammetric determination of salbutamol on a glassy carbon electrode coated with a nanomaterial thin film

A rapid and convenient electrochemical method is described for the determination of salbutamol based on multi-carbon nanotubes (MWNT) film coated glassy carbon electrode (GCE). The electrochemical behavior of salbutamol at this modified electrode was studied by square wave voltammetry, which indicated that the oxidation peak potential of salbutamol shifted on 40 mV to less positive potential and the peak current increased 4.5 fold, in contrast to that at a bare electrode. Various experimental parameters such as pH value of supporting electrolyte, the amount of modifier, and accumulation time were optimized. Under optimal measurement conditions, there is a good linear relationship between the peak current (I _pa) and salbutamol concentration in the range from 8.0 × 10⁻⁷ to 1.0 × 10⁻⁵ M, and the detection limit is 2.0 × 10⁻⁷ M (S/N = 3) at 2 min accumulation. The method has been successfully employed to detect salbutamol in pharmaceutical formulations.     

Covalent modification of glassy carbon electrode with cysteine for the determination of dopamine in the presence of ascorbic acid

A covalently modified glassy carbon electrode with cysteine has been fabricated via an electrochemical oxidation procedure and was applied to induce the electrochemical differentiation between dopamine (DA) and ascorbic acid (AA). Based on the electrostatic interactions between the negatively charged groups on the electrode surface and DA and AA, the modified electrode enhanced the oxidation of DA, reducing the overpotential by 180 mV, and hindered the oxidation of AA, shifting the oxidation potential positively by 170 mV. The peak current for DA at the modified electrode was greatly enhanced and that for AA was significantly decreased, which allows the determination of DA in the presence of AA. The differential pulse peak current was linearly dependent on DA concentration over the range of 5 × 10⁻⁶–2 × 10⁻⁴ mol L⁻¹. The detection limit was 1.8 × 10⁻⁶ mol L⁻¹. The selectivity and sensitivity for dopamine is due to charge discrimination and analyte accumulation. The modified electrode has been applied to the determination of DA in the presence of AA. Correspondence: L. Zhang, Department of Chemistry, College of Life and Environmental Science, Shanghai Normal University, Guilin Rd 100, Shanghai 200234, P.R. China     

Electrocatalytic oxidation and determination of norepinephrine in the presence of ascorbic and uric acids at a poly (Evans Blue)—modified glassy carbon electrode

A sensitive and selective electrochemical method for the determination of norepinephrine using a poly (Evans Blue) film-modified glassy carbon electrode was developed. The polymer film-modified electrode shows excellent electrocatalytic activity toward the oxidation of norepinephrine (NE) in phosphate buffer solution (pH 5.0). The linear range of 5.0 × 10⁻⁷–1.8 × 10⁻⁵ M and detection limit of 3.5 × 10⁻⁸ M were observed for the determination of NE in pH 5.0 phosphate buffer solutions. The interference studies showed that the modified electrode had excellent selectivity for the determination of NE in the presence of large excess of ascorbic acid (AA) and uric acid (UA). The differences of the oxidation peak potentials for NE-AA and NE-UA were about 175 and 172 mV, respectively. The resolution is large enough to determine AA, NE and UA individually. This work provides a simple and easy approach to selective detection of NE in the presence of AA and UA in physiological samples. The article is published in the original.