Electrochemical determination of bisphenol A at Mg-Al-CO3 layered double hydroxide modified glassy carbon electrode

The electrochemical behavior of bisphenol A (BPA) was investigated on Mg-Al layered double hydroxide (LDH) modified glassy carbon electrode (GCE) by cyclic voltammetry (CV), differential pulse voltammetry (DPV), linear sweep voltammetry (LSV) and chronocoulometry (CC). The cyclic voltammogram of BPA on the modified electrode exhibited a well defined anodic peak at 0.454 V in 0.1 M pH 8.0 phosphate buffer solution (PBS). The experimental parameters were optimized and the kinetic parameters were investigated. The probable oxidation mechanism was proposed. Under the optimized conditions, the oxidation peak current was proportional to BPA concentration in the range from 1 × 10⁻⁸ to 1.05 × 10⁻⁶ M with the correlation coefficient of 0.9959. The detection limit was 5.0 × 10⁻⁹ M (S/N = 3). The fabricated electrode showed good reproducibility, stability and anti-interference. The proposed method was successfully applied to determine BPA in plastic products and the results were satisfactory.     

Electrochemical behavior of catechol, resorcinol and hydroquinone at graphene–chitosan composite film modified glassy carbon electrode and their simultaneous determination in water samples

Graphene–chitosan composite film modified glassy carbon electrode was prepared and characterized. The fabricated electrode showed excellent electrochemical catalytic activities towards the oxidation of catechol (CT), resorcinol (RS) and hydroquinone (HQ). The oxidation overpotentials of CT, RS and HQ decreased significantly and the corresponding oxidation currents increased remarkably compared with those obtained at the bare GCE and chitosan modified GCE. Some kinetic parameters, such as the electron transfer number (n), proton transfer number (m), charge transfer coefficient (α) and the apparent heterogeneous electron transfer rate constant (k_s), were calculated. Differential pulse voltammetry was used for the simultaneous determination of CT, RS and HQ in their ternary mixture. The peak-to-peak potential separations between CT and RS, RS and HQ, and HQ and CT were 0.388, 0.484 and 0.096 V, respectively. The calibration curves for CT, RS and HQ were obtained in the range of 1 × 10⁻⁶ to 4 × 10⁻⁴, 1 × 10⁻⁶ to 5.5 × 10⁻⁴ and 1 × 10⁻⁶ to 3 × 10⁻⁴ mol L⁻¹, respectively. The detection limits were 7.5 × 10⁻⁷ mol L⁻¹ (S/N = 3).     

Simultaneous determination of dopamine and uric acid on nafion/sodium dodecylbenzenesulfonate composite film modified glassy carbon electrode

A novel electrochemical sensor has been constructed by using a glassy carbon electrode (GCE) coated with nafion/sodium dodecylbenzenesulfonate (SDBS). Differential pulse voltammetry (DPV) was used to study the electrochemical behaviors of dopamine (DA) and uric acid (UA). An optimum of 5 mM SDBS together with 0.05 wt% of nafion was used to improve the resolution and the determination sensitivity successfully. In 0.1 M phosphate buffer solution (pH 6.5), the modified electrode exhibited high electrocatalytical activity toward the oxidation of DA and UA with obvious reduction of overpotential. Compared with bare GCE, the modified electrode resolved the voltammetric response of DA and UA into two well-defined voltammetric peaks by DPV, which can be used for simultaneous determination of these species in mixture. The peak currents obtained from DPV were linearly related to the concentrations of DA and UA in the ranges of 4.0 × 10⁻⁷–8.0 × 10⁻⁵ M and 4.0 × 10⁻⁶–8.0 × 10⁻⁴ M, respectively. The detection limit of DA and UA (signal-to-noise ration was 3) were 5.0 × 10⁻⁸ and 4.0 × 10⁻⁷ M, respectively.     

银掺杂改性蒙脱土修饰电极测定L-色氨酸的电化学行为

以十八烷基三甲基溴化铵(OTAB)、银氨溶液对蒙脱土掺杂改性制得样品,用作电极修饰的材料。采用XRD、SEM、能谱法和交流阻抗法技术对样品表征,以循环伏安法、方波溶出伏安法探究改性蒙脱土修饰电极上L-色氨酸的电化学行为。结果表明,吸附和扩散对该电化学行为均有影响,反应转移的电子数n与质子数m为1,电极有效面积0.11 cm~2,扩散系数1.76×10-5cm~2/s。当CL-色氨酸在9.0×10-7~8.0×10-4mol/L时,其浓度与其氧化峰电流呈线性关系,检出限为6.53×10-7mol/L,加标回收率为94.3%~101.9%。     

银掺杂改性蒙脱土修饰电极测定L-色氨酸的电化学行为

以十八烷基三甲基溴化铵(OTAB)、银氨溶液对蒙脱土掺杂改性制得样品,用作电极修饰的材料。采用XRD、SEM、能谱法和交流阻抗法技术对样品表征,以循环伏安法、方波溶出伏安法探究改性蒙脱土修饰电极上L-色氨酸的电化学行为。结果表明,吸附和扩散对该电化学行为均有影响,反应转移的电子数n与质子数m为1,电极有效面积0.11 cm²,扩散系数1.76×10-5cm2,扩散系数1.76×10-5cm²/s。当CL-色氨酸在9.0×10-72/s。当CL-色氨酸在9.0×10-7⁸.0×10-4mol/L时,其浓度与其氧化峰电流呈线性关系,检出限为6.53×10-7mol/L,加标回收率为94.3%8.0×10-4mol/L时,其浓度与其氧化峰电流呈线性关系,检出限为6.53×10-7mol/L,加标回收率为94.3%¹01.9%。     

Polyaniline Langmuir-Blodgett film modified glassy carbon electrode as a voltammetric sensor for determination of Ag ions

A highly sensitive electrochemical sensor made of a glassy carbon electrode (GCE) coated with a Langmuir-Blodgett film (LB) containing polyaniline (PAn) doped with p-toluenesulfonic acid (PTSA) (LB/PAn-PTSA/GCE) has been used for the detection of trace concentrations of Ag⁺. UV-vis absorption spectra indicated that the PAn was doped by PTSA. The surface morphology of the PAn LB film was characterized by atomic force microscopy (AFM). The electrochemical properties of this LB/PAn-PTSA/GCE were studied using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry. The LB/PAn-PTSA/GCE was used as a voltammetric sensor for determination of trace Ag⁺ at pH 5.0 using linear scanning stripping voltammetry. Under the optimal experimental conditions, the stripping current was proportional to the Ag⁺ concentration over the range from 6.0 × 10⁻¹⁰ mol L⁻¹ to 1.0 × 10⁻⁶ mol L⁻¹, with a detection limit of 4.0 × 10⁻¹⁰ mol L⁻¹. The high sensitivity, selectivity, and stability of this LB/PAn-PTSA/GCE also demonstrated its practical utility for simple, rapid and economical determination of Ag⁺ in water samples.     

Electrochemical study on cobalt film modified glassy carbon electrode and its application

A novel electroactive material for ascorbic acid (AA) determination was successfully prepared by plating/potential cycling method. The cobalt film was first deposited on the surface of glassy carbon electrode (GCE) in CoSO₄ solution by potential cycling, and then a cobalt film on the surface of GCE was activated by potential cycling in 0.1 mol L⁻¹ NaOH. The electrochemical performance of the resulted film (Co/GCE) and factors affecting its electrochemical activity were investigated by cyclic voltammetry and amperometry. This film electrode exhibited good electrocatalytic activity to the oxidation of AA. This biosensor had a fast response of AA less than 3 s and excellent linear relationships were obtained in the concentration range of 3 × 10⁻⁷ to 1 × 10⁻⁴ mol L⁻¹ with a detection limit of 2 × 10⁻⁷ mol L⁻¹ (S/N = 3) under the optimum conditions. Moreover, the selectivity, stability and reproducibility of this biosensor were evaluated with satisfactory results.     

Simultaneous voltammetric determination of tramadol and acetaminophen using carbon nanoparticles modified glassy carbon electrode

A sensitive and selective electrochemical sensor was fabricated via the drop-casting of carbon nanoparticles (CNPs) suspension onto a glassy carbon electrode (GCE). The application of this sensor was investigated in simultaneous determination of acetaminophen (ACE) and tramadol (TRA) drugs in pharmaceutical dosage form and ACE determination in human plasma. In order to study the electrochemical behaviors of the drugs, cyclic and differential pulse voltammetric studies of ACE and TRA were carried out at the surfaces of the modified GCE (MGCE) and the bare GCE. The dependence of peak currents and potentials on pH, concentration and the potential scan rate were investigated for these compounds at the surface of MGCE. Atomic force microscopy (AFM) was used for the characterization of the film modifier and its morphology on the surface of GCE. The results of the electrochemical investigations showed that CNPs, via a thin layer model based on the diffusion within a porous layer, enhanced the electroactive surface area and caused a remarkable increase in the peak currents. The thin layer of the modifier showed a catalytic effect and accelerated the rate of the electron transfer process. Application of the MGCE resulted in a sensitivity enhancement and a considerable decrease in the anodic overpotential, leading to negative shifts in peak potentials. An optimum electrochemical response was obtained for the sensor in the buffered solution of pH 7.0 and using 2 μL CNPs suspension cast on the surface of GCE. Using differential pulse voltammetry, the prepared sensor showed good sensitivity and selectivity for the determination of ACE and TRA in wide linear ranges of 0.1-100 and 10-1000 μM, respectively. The resulted detection limits for ACE and TRA was 0.05 and 1 μM, respectively. The CNPs modified GCE was successfully applied for ACE and TRA determinations in pharmaceutical dosage forms and also for the determination of ACE in human plasma.     

Electrochemical behavior and adsorptive stripping voltammetric determination of quercetin at multi-wall carbon nanotubes-modified paraffin-impregnated graphite disk electrode

Multi-wall carbon nanotubes-modified paraffin-impregnated graphite disk was fabricated by using choline bond and catalyzer (MWCNT/Ch/WGE), and the properties were, respectively, investigated by field emission scanning electron microscope (FE-SEM) and X-ray photoelectron spectroscopy (XPS). Electrochemical behavior of quercetin was studied in detail by FE-SEM, UV-spectroelectrochemical and various electrochemical methods, which related with the two catechol hydroxyl groups and the other three hydroxyl groups, the former is electron-donating group with a two electron two proton reversible reaction, and is pH dependent. A highly sensitive adsorptive stripping voltammetric measurement (AdSV) for quercetin was also shown at this electrode. On the optimum conditions, the adsorptive stripping response of the peak (E = 0.15 V, 3 min accumulation) was proportional to the concentration in a range of 9.0 × 10⁻⁹ to 4.0 × 10⁻⁵ M. A detection limit of 4.8 × 10⁻⁹ M was obtained with a signal-to-noise ratio (s/n) of 3 and a good precision (R.S.D.: 2.1%, n: 9). Such attractive ability of MWCNT/Ch/WGE suggests a great promise for a quercetin amperometric sensor.     

Electrochemiluminescent behavior of luminol on the glassy carbon electrode modified with CoTPP/MWNT composite film

A glassy carbon electrode (GCE) modified with cobalt(II) meso-tetraphenylporphrine/multiwall-carbon nanotube (CoTPP/MWNT) was applied to investigate the electrochemiluminescent (ECL) behavior of luminol. The ECL intensity of luminol was found to be increased greatly on this modified electrode. The presence of cobalt(II) meso-tetraphenylporphrine (CoTPP) can catalyze the reduction of oxygen on the electrode surface to produce HOO⁻, which can increase the ECL intensity of luminol. Moreover, MWNT can provide the more effective area of the electrode, and can act as a promoter to enhance the electrochemical reaction. The proposed method enables a detection limit for luminol of 1.0 × 10⁻⁸ mol/L in the neutral solution. Under the optimum condition, the enhanced ECL intensity of luminol by H₂O₂ had a linear relationship with the concentration of H₂O₂ in the range of 1.0 × 10⁻⁷ to 8.0 × 10⁻⁸ mol/L with the detection limit of 5.0 × 10⁻⁹ mol/L.     

Electrochemical modification of glassy carbon electrode by poly-4-nitroaniline and its application for determination of copper(II)

Electrochemical modification of glassy carbon (GC) electrode by poly-4-nitroaniline (P4NA), electrochemical reduction of P4NA and applicability of electrode modified in this way for determination of copper(II) (Cu(II)) is reported in this study. Electrochemical surface modification was performed by cyclic voltammetry in the potential range between +0.9 V and +1.4 V vs. Ag/Ag⁺ (in 10 mM AgNO₃) at the scan rate of 100 mV/s by 100 cycles in non-aqueous media. In order to provide electrochemical reduction of nitro groups on the P4NA-modified GC electrode surface (P4NA/GC), the cyclic voltammograms inducing/evidencing the reduction of nitro groups were performed in the potential range between −0.1 V and −0.8 V vs. Ag/AgCl/(sat.KCl) at the scan rate of 100 mV/s. The reduced P4NA/GC surfaces (Reduced-P4NA/GC) were treated with aqueous solution of nitrilotriacetic acid. The sensitivity of GC electrode modified in described way towards Cu(II) was investigated in Britton-Robinson buffer solution, pH 5.0. The potentiometric generic pulse technique was applied as innovative electrochemical method for detection of analytical signal. It was shown that GC electrodes modified in here described way will be suitable for the determination of Cu(II) in technological waste water and/or some other solutions containing Cu(II) ions.     

Electrochemical determination of thiamazole at a multi-wall carbon nanotube modified glassy carbon electrode

A simple and convenient method is described for voltammetric determination of thiamazole, a commonly used anti-hyperthyroid drug, based on its electrochemical oxidation at a multi-wall carbon nanotube modified glassy carbon electrode. Under optimized conditions, the proposed method exhibited acceptable analytical performances in terms of linearity (over the concentration range from 1.0 × 10⁻⁷ to 5.0 × 10⁻⁴ mol L⁻¹, r = 0.9983), detection limit (3.0 × 10⁻⁸ mol L⁻¹) and reproducibility (RSD = 2.64%, n = 10, for 5.0 × 10⁻⁵ mol L⁻¹ thiamazole). To further validate its possible application, the method was used for the quantification of thiamazole in pharmaceutical formulations and biological fluids.     

基于多壁碳纳米管修饰电极的磺胺的电化学检测

运用线性扫描伏安法(LSV)研究了磺胺(SA)在多壁碳纳米管修饰电极(MWNTs/GCE)上的电化学行为,探讨并确定了修饰体积和浓度、支持基质种类、最佳pH值、富集电位和时间等磺胺的最佳检测条件。结果表明,在pH=8.0的Na2HPO4-NaH2PO4缓冲体系中,磺胺在多壁碳纳米管修饰电极上检测到一个不可逆的氧化峰,且在1.0×10-5².0×10-4mol/L浓度范围内,磺胺氧化峰电流与其浓度呈现良好的线性关系,线性回归方程为Ip(μA)=0.493 6×C(μmol/L)+9.984 1,相关系数为R=0.996 3,检测下限为8.0×10-6mol/L,平行测定的相对误差(RSD)小于1.463%(n=8),样品平均加标回收率为99.21%2.0×10-4mol/L浓度范围内,磺胺氧化峰电流与其浓度呈现良好的线性关系,线性回归方程为Ip(μA)=0.493 6×C(μmol/L)+9.984 1,相关系数为R=0.996 3,检测下限为8.0×10-6mol/L,平行测定的相对误差(RSD)小于1.463%(n=8),样品平均加标回收率为99.21%¹00.93%。     

基于多壁碳纳米管修饰电极的磺胺的电化学检测

运用线性扫描伏安法(LSV)研究了磺胺(SA)在多壁碳纳米管修饰电极(MWNTs/GCE)上的电化学行为,探讨并确定了修饰体积和浓度、支持基质种类、最佳pH值、富集电位和时间等磺胺的最佳检测条件。结果表明,在pH=8.0的Na2HPO4-NaH2PO4缓冲体系中,磺胺在多壁碳纳米管修饰电极上检测到一个不可逆的氧化峰,且在1.0×10-5~2.0×10-4mol/L浓度范围内,磺胺氧化峰电流与其浓度呈现良好的线性关系,线性回归方程为Ip(μA)=0.493 6×C(μmol/L)+9.984 1,相关系数为R=0.996 3,检测下限为8.0×10-6mol/L,平行测定的相对误差(RSD)小于1.463%(n=8),样品平均加标回收率为99.21%~100.93%。     

Electrochemical simultaneous determination of nitrophenol isomers at nano-gold modified glassy carbon electrode

A novel method for simultaneous determination of nitrophenol isomers at nano-gold modified glassy carbon electrode has been developed. The gold nanoparticles were directly electrodeposited onto the glassy carbon electrode via a constant potential −0.2 V (vs. SCE) for 60 s from 0.1 mol L⁻¹ KNO₃ containing 0.4 g L⁻¹ HAuCl₄. The resulting electrode (nano-Au/GCE) was characterized with scanning electron microscopy (SEM). The electrochemistry response of nitrophenol isomers at the nano-Au/GCE was studied. The result indicated that o-, m-, and p- nitrophenol are separated entirely at nano-Au/GCE, and a semi-derivative voltammetric technology was adopted to enhance the determination sensitivity. This modified electrode could be applied to direct simultaneous voltammetric determination of nitrophenol isomers in water samples without preseparation with higher sensitivity.     

Electrochemical sensing based on graphene oxide/Prussian blue hybrid film modified electrode

A novel graphene oxide (GO)/Prussian blue (PB) hybrid film was constructed by electropolymerizing Prussian blue onto the GO modified glassy carbon electrode, and its electrochemical behaviors were studied. Raman spectra were used to investigate the successful formation of the GO/PB hybrid film. Electrochemical experiments showed that the graphene oxide greatly enhanced electrochemical reactivity of the PB. Moreover, a much higher Prussian blue (PB) loading (6.388 × 10⁻⁸ mol cm⁻²) is obtained as compared to the bare glass carbon surface (3.204 × 10⁻⁹ mol cm⁻²). The GO/PB hybrid film modified electrode was used for the sensitive detection of hydrogen peroxide. The sensor exhibited a wide linearity range from 5.0 × 10⁻⁶ to 1.2 × 10⁻³ M with a detection limit of 1.22 × 10⁻⁷ M (S/N = 3), high sensitivity of 408.7 μA mM⁻¹ cm⁻² and good reproducibility. Furthermore, with glucose oxidase (GOD) as a model, the GO/PB/GOD/chitosan composite-modified electrode was also constructed.The resulting biosensor exhibited good amperometric response to glucose with linear range from 0.1 to 13.5 mM at 0.1 V, good reproducibility and detection limit of 3.43 × 10⁻⁷ M (S/N = 3). In addition, the biosensor presented high selectivity and long-term stability. Therefore, the PB/GO hybrid films-based modified electrode may hold great promise for electrochemical sensing and biosensing applications.     

Electrochemical behavior of phenol in alkaline media at hydrotalcite-like clay/anionic surfactants/glassy carbon modified electrode

The electrochemical behavior of phenol, using glassy carbon (GC) modified electrodes containing a hydrotalcite (HT)-like clay and anionic surfactants such as sodium octyl sulfate (SOS), sodium dodecyl sulfate (SDS), or sodium dodecylbenzenesulfonate (SDBS) in alkaline media, has been examined. Phenol oxidation at the modified electrodes, after a time accumulation under open circuit conditions, promotes increments of the current and shifts the oxidation potential to less positive values, compared to phenol oxidation at HT-GC or GC electrodes. The phenol oxidation is favored by the presence of surfactants in the films. The results suggest that the surfactant molecules intercalate between the HT layers, yielding a hydrophobic clay capable of preconcentrating phenol molecules. X-ray diffraction analyses showed a larger spacing of the HT layers when the surfactant intercalates between them. Cyclic voltammograms have shown that the SOS-HT-GC modified electrode exhibits short-lived activity for phenol oxidation as a consequence of surface fouling, while the SDS-HT-GC and SDBS-HT-GC modified electrodes showed a more stable behavior. The SDBS-HT-GC modified electrode was the most effective adsorbing phenol, since the charge (Q), obtained from the integration of the anodic peak current of the phenol, is higher at this modified electrode. This is probably because the adsolubilization capacity of phenol on the SDBS-HT-GC electrode is higher than on SDS-HT-GC electrode.     

Electrochemical sensors for hemoglobin and myoglobin detection based on methylene blue-multiwalled carbon nanotubes nanohybrid-modified glassy carbon electrode

An effective electrochemical sensors for hemoglobin (Hb) and myoglobin (Mb) detection was firstly developed using a simple procedure of self-assembled methylene blue-multiwalled carbon nanotubes (MB-MWNTs) nanohybrid modified on glassy carbon electrode without using any enzymes immobilization. The direct electrochemical and electrocatalytic behaviors of the modified electrode were studied using cyclic voltammetry (CV) and flow injection analysis (FIA) with amperometry. The performance of the sensor was investigated and optimized and the system was evaluated by monitoring Hb and Mb concentrations. The developed MB-MWNTs nanohybrid modified electrode showed excellent electrocatalytic activity for reduction of Hb and Mb with good stability, sensitivity and reproducibility (RSD = 3.05% and 4.5% for 50 successive injections of Hb and Mb, respectively). Under optimal conditions, the catalytic currents are linearly proportional to the concentrations of Hb and Mb in the wide range from 5 nM to 2 μM and 0.1 to 3 μM, and the corresponding detection limits are 1.5 nM and 20 nM (S/N = 3), respectively. This approach provides improved detection limit over other previous works and may provide a novel and efficient platform for the fabrication of sensors for other heme proteins.