Electrocatalytic oxidation of dopamine at an ionic liquid modified carbon paste electrode and its analytical application

A room-temperature ionic liquid N-butylpyridinium hexafluorophosphate was used as a binder to construct an ionic liquid modified carbon paste electrode, which was characterized by scanning electron microscopy and electrochemical impedance spectroscopy. The ionic liquid carbon paste electrode (IL-CPE) showed enhanced electrochemical response and strong analytical activity towards the electrochemical oxidation of dopamine (DA). A pair of well-defined quasireversible redox peaks of DA appeared, with the redox peaks located at 215 mV (E _pa) and 151 mV (E _pc) (vs. the saturated calomel electrode, SCE) in pH 6.0 phosphate buffer solution. The formal potential (E ^0′) was calculated as 183 mV (vs. SCE) and the peak-to-peak separation as 64 mV. The electrochemical behavior of DA on the IL-CPE was carefully investigated. Under the optimal conditions, the anodic peak currents increased linearly with the concentration of DA in the range 1.0 × 10⁻⁶–8.0 × 10⁻⁴ mol/L and the detection limit was calculated as 7.0 × 10⁻⁷ mol/L (3σ). The interferences of foreign substances were investigated and the proposed method was successfully applied to the determination of DA injection samples. The IL-CPE fabricated was sensitive, selective and showed good ability to distinguish the coexisting ascorbic acid and uric acid.     

A sensitive electrochemical sensor for detection of rutin based on a gold nanocage‐modified electrode

In this article, an electrochemical sensor based on a gold nanocage (AuNC)‐modified carbon ionic liquid electrode (CILE) was fabricated and applied to the sensitive rutin determination. The presence of AuNCs on the electrode surface greatly improved the electrochemical performance of the working electrode due to its specific microstructure and high metal conductivity. Electrochemical behavior of rutin on AuNCs/CILE was studied using cyclic voltammetry and differential pulse voltammetry with the related electrochemical parameters calculated. Under the optimal experimental conditions, the oxidation peak current of rutin and its concentration had good linear relationship in the range from 4.0 × 10^?9 to 7.0 × 10^?4 mol/L with a low detection limit of 1.33 × 10^?9 mol/L (3σ). This fabricated AuNCs/CILE was applied to direct detection of the rutin concentration in drug samples with satisfactory results, showing the real application of AuNCs in the field of chemically modified electrodes.     

Electrochemical determination of bisphenol A based on PHD/MWCNTs modified glassy carbon electrode

A novel electrochemical sensor for the determination of bisphenol A (BPA) was fabricated by block polyelectrolyte composite films, which composed of diblock polyelectrolyte poly (2-hydroxyethyl methacrylate)-b-poly (2-(dimethylamino) ethyl methacrylate) (PHEMA-b-PDMAEMA, noted as PHD in the later content) and multi-walled carbon nanotubes (MWCNTs). The tertiary amino groups of PDMAEMA can be protonated at physiological pH. The protonated PDMAEMA can thus interact with the negatively charged BPA through electrostatic attraction to increase the BPA sorption capacity and enhance the ability for highly sensitive detection of BPA. The PHD/MWCNTs composite films combine the electrocatalytic property of MWCNTs and the electrostatic attraction of protonated PHD. Because of the above-mentioned excellent property of the composite films, the PHD/MWCNTs/glassy carbon electrode exhibited good electrocatalytic activity to electrooxidation of BPA. The wide linear response range of the BPA sensor was from 4.56 × 10^?5 g L^?1 to 2.28 × 10^?2 g L^?1 with a lower detection limit of 2.28 × 10^?6 g L^?1 (S/N = 3) and high sensitivity 2442.86 μA L g^?1 cm^?2. The current reached the steady-state current with a shorter response time less than 4 s. The proposed method was successfully applied to determine BPA in real samples (PVC food package, milk, tap water and pond water) and satisfactory results were obtained. These results indicated that the block polyelectrolyte composite have potential applicability of the BPA sensor.     

Electrochemical behaviors of guanosine on carbon ionic liquid electrode and its determination

The electrochemical behaviors of guanosine on the ionic liquid of N-butylpyridinium hexafluorophosphate (BPPF₆) modified carbon paste electrode (CPE) was studied in this paper and further used for guanosine detection. Guanosine showed an adsorption irreversible oxidation process on the carbon ionic liquid electrode (CILE) with the oxidation peak potential located at 1.12 V (vs. SCE) in a pH 4.5 Britton-Robinson (B-R) buffer solution. Compared with that on the traditional carbon paste electrode, small shift of the oxidation peak potentials appeared but with a great increment of the oxidation peak current on the CILE, which was due to the presence of ionic liquid in the modified electrode adsorbed the guanosine on the surface and promoted the electrochemical response. The electrochemical parameters such as the electron transfer coefficient (α), the electron transfer number (n), and the electrode reaction standard rate constant (k_s) were calculated as 0.74, 1.9 and 1.26 × 10⁻⁴ s⁻¹, respectively. Under the optimal conditions the oxidation peak current showed a good linear relationship with the guanosine concentration in the range from 1.0 × 10⁻⁶ to 1.0 × 10⁻⁴ mol/L by cyclic voltammetry with the detection limit of 2.61 × 10⁻⁷ mol/L (3σ). The common coexisting substances showed no interferences to the guanosine oxidation. The CILE showed good ability to distinguish the electrochemical response of guanosine and guanine in the mixture solution. The urine samples were further detected by the proposed method with satisfactory results.     

金-石墨烯修饰电极电化学检测塑料瓶中双酚A

在离子液体碳糊电极(CILE)表面上采用一步电还原法制备了纳米金(nAu)-石墨烯(GR)复合膜修饰电极(nAu-GR/CILE).研究了双酚A(BPA)在nAu-GR/CILE上的电化学行为,BPA的电极反应过程为受吸附控制的不可逆过程;采用示差脉冲伏安法研究了BPA氧化峰电流和浓度之间的关系,在0.08～400.0...     

Poly(methylene blue) functionalized graphene modified carbon ionic liquid electrode for the electrochemical detection of dopamine

An ionic liquid 1-butylpyridinium hexafluorophosphate based carbon ionic liquid electrode (CILE) was used as the substrate electrode and a poly(methylene blue) (PMB) functionalized graphene (GR) composite film was co-electrodeposited on CILE surface by cyclic voltammetry. The PMB–GR/CILE exhibited better electrochemical performances with higher conductivity and lower electron transfer resistance. Electrochemical behavior of dopamine (DA) was further investigated by cyclic voltammetry and a pair of well-defined redox peaks appeared with the peak-to-peak separation (ΔE_p) as 0.058 V in 0.1 mol L⁻¹ pH 6.0 phosphate buffer solution, which proved a fast quasi-reversible electron transfer process on the modified electrode. Electrochemical parameters of DA on PMB–GR/CILE were calculated with the electron transfer number as 1.83, the charge transfer coefficients as 0.70, the apparent heterogeneous electron transfer rate constant as 1.72 s⁻¹ and the diffusional coefficient (D) as 3.45 × 10⁻⁴ cm² s⁻¹, respectively. Under the optimal conditions with differential pulse voltammetric measurement, the linear relationship between the oxidation peak current of DA and its concentration was obtained in the range from 0.02 to 800.0 μmol L⁻¹ with the detection limit as 5.6 nmol L⁻¹ (3σ). The coexisting substances exhibited no interference and PMB–GR/CILE was applied to the detection of DA injection samples and human urine samples with satisfactory results.     

抗坏血酸在离子液体修饰玻碳电极上的电化学行为

利用离子液体1-丁基-3-甲基咪唑四氟硼酸盐(BMIMBF4)对玻碳电极(GCE)进行修饰,制备了BMI-MBF4/GCE电极.在0.1mol/L的磷酸盐缓冲溶液中,采用循环伏安法研究了抗坏血酸在BMIMBF4/GCE电极和裸玻碳电极(GCE)上的电化学行为.结果表明,pH=5.7的磷酸盐缓冲溶液为最佳测定底液,最佳富集时间为120s;BMIMBF4/GCE对抗坏血酸的氧化反应有很好的电化学催化作用.抗坏血酸的氧化峰电流与其浓度在2.0×10-4～1.0×10-2 mol/L的范围内呈良好的线性关系,相对标准偏差为4.53%(n=5).     

Application of multi-walled carbon nanotubes modified carbon ionic liquid electrode for electrocatalytic oxidation of dopamine

A simple, sensitive, and reliable method based on a multi-walled carbon nanotubes (MWNTs) modified carbon ionic liquid electrode (CILE) has been successfully developed for determination of dopamine (DA) in the presence of ascorbic acid (AA). The acid-treated MWNTs with carboxylic acid functional groups could promote the electron-transfer reaction of DA and inhibit the voltammetric response of AA. Due to the good performance of the ionic liquid, the electrochemical response of DA on the MWNTs/CILE was better than that of other MWNTs modified electrodes. Under the optimum conditions a linear calibration plot was obtained in the range 5.0×10(-8) to 2.0×10(-4) mol L(-1) and the detection limit was 1.0×10(-8) mol L(-1).     

氧化石墨烯修饰碳离子液体电极同时测定鸟嘌呤和腺嘌呤

以离子液体1-丁基-3-甲基咪唑六氟磷酸盐为粘合剂制备了碳糊电极,然后将氧化石墨烯滴涂到碳糊电极表面制成了一种新型的氧化石墨烯修饰碳离子液体电极。研究了鸟嘌呤和腺嘌呤在修饰电极上的电化学行为。实验结果表明,在0.1 mol/L醋酸盐缓冲溶液中(pH4.5),鸟嘌呤和腺嘌呤在该修饰电极上具有良好的电化学行为,在2.0×10-7～1.5×10-5mol/L浓度范围内鸟嘌呤和腺嘌呤的浓度在该电极上与电化学响应信号呈良好的线性关系,相关系数分别为为0.992和0.996。信噪比为3时,检出限为1.0×10-8mol/L。     

Sensitive voltammetric determination of rutin at an ionic liquid modified carbon paste electrode

An ionic liquid modified carbon paste electrode (IL/CPE) had been fabricated by using hydrophilic ionic liquid 1-amyl-3-methylimidazolium bromide ([AMIM]Br) as a modifier. The IL/CPE was characterized by scanning electron microscope and voltammetry. Electrochemical behavior of rutin at the IL/CPE had been investigated in pH 3.29 Britton-Robinson (B-R) buffer solution by cyclic voltammetry (CV) and square wave voltammetry (SWV). The experimental results suggested that the modified electrode exhibited an electrocatalytic activity toward the redox of rutin. The electron transfer coefficient (α) and the standard rate constant (k_s) of rutin at the modified electrode were calculated. Under the selected conditions, the reduction peak current was linearly dependent on the concentration of rutin in the range of 4.0 × 10⁻⁸ to 1.0 × 10⁻⁵ mol L⁻¹ (r = 0.9998), with a detection limit of 1.0 × 10⁻⁸ mol L⁻¹ (S/N = 3). The relative standard deviation (R.S.D.) for six times successful determination of 8.0 × 10⁻⁷ mol L⁻¹ rutin was 1.2%. The proposed method was applied to determine rutin in tablet and urine sample. In addition, the IL/CPE exhibited a distinct advantage of simple preparation, surface renewal, good reproducibility and good stability.     

A dandelion-like carbon microsphere/MnO2 nanosheets composite for supercapacitors

This article reported the electrochemical performance of a novel cabon microsphere/MnO₂ nanosheets (CMS/MnO₂) composite prepared by a in situ self-limiting deposition method under hydrothermal condition. The results of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed that MnO₂ nanosheets homogeneously grew onto the surface of CMS to form a loose-packed and dandelion-like core/shell microstructure. The unique microstructure plays a basic role in electrochemical accessibility of electrolyte to MnO₂ active material and a fast diffusion rate within the redox phase. The results of cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectrometry indicated that the prepared CMS/MnO₂ composite presented high capacitance of 181 F·g⁻¹ and long cycle life of 61% capacity retention after 2000 charge/discharge cycles in 1 mol/L Na₂SO₄ solution, which show strong promise for high-rate electrochemical capacitive energy storage applications.     

Electroanalytical quantification of total dsDNA extracted from human sample using,an ionic liquid modified,carbon nanotubes paste electrode

Direct electrochemistry of dsDNA has been achieved by using an ionic liquid 1-butyl-4-methylpyridinium hexafluorophosphate modified carbon nanotubes paste electrode (IL-CNTPE). Oxidation peaks appeared at 0.93 and 1.26 V (vs. Ag/AgCl) on the IL- CNTPE after preconcentration of dsDNA in pH 5.0 acetate buffer, which were attributed to the oxidation of guanine and adenine residues on the dsDNA molecule structure. Based on the signal of guanine, under the optimal conditions, very low levels of dsDNA can be detected after 60 s accumulation with detection limits of 0.249 mg L⁻ 16 pM. Additionally, human DNA from a healthy volunteer is determined by use of the IL-CNTPE and it is found to be 40 ± 2, 14 pM.     

Fabrication of ferrocene functionalised ionic liquid/carbon nanotube nanocomposite modified carbon-ceramic electrode: application to the determination of hydrazine

A novel ionic liquid, 1-(ferrocenyl butyl)-3-methylimidazolium tetrafluoroborate (Fc-IL), was synthesised. The nanocomposite of Fc-IL and multi-walled carbon nanotubes (MWCNTs) was constructed and used for surface modification of carbon-ceramic electrode. The modified electrode was applied to the determination of hydrazine. Operational parameters such as pH of the solution, ionic liquid volume and amount of carbon nanotubes, which affect the analytical performance of the modified electrode, were optimised. The linear range of the modified electrode toward hydrazine concentration was 0.96–106.10 μg L^–1 with a detection limit of 0.64 μg L^–1 (S/N = 3). The modified electrode displayed high repeatability, reproducibility, long-term life time and low response time (<3 s). The applicability of this method was further tested by analysing the hydrazine content in boiler-feed water samples containing different concentrations of hydrazine and the results were in good agreement with the spectrophotometry method.     

Dendrimer-rhodium nanoparticle modified glassy carbon electrode for amperometric detection of hydrogen peroxide

Metallic nanoparticles of rhodium were prepared by using the newly synthesized N,N-bis-succinamide-based dendrimer as stabilizers. The Rh nanoparticles were spherical shaped with a particle size of ∼2 nm. The dendrimer Rh-encapsulated nanoparticles (Rh-DENs) were immobilized on glassy carbon electrode (GCE) and their electrocatalytic activity towards hydrogen peroxide reduction was investigated using cyclic voltammetry and chronoamperometry. The Rh-DENs modified GCE showed excellent electrocatalytic activity for hydrogen peroxide reduction reactions. The steady-state cathodic current response of the modified electrode at −0.3 V (vs SCE) in phosphate buffer (pH 7.0) showed a linear response to hydrogen peroxide concentration ranging from 8 to 30 μM with a detection limit and sensitivity of 5 μM and 0.03103 × 10⁻⁶ A μM⁻¹, respectively.     

Direct electrochemistry of glucose oxidase based on its direct immobilization on carbon ionic liquid electrode and glucose sensing

Direct electrochemistry of glucose oxidase (GOx) has been achieved by its direct immobilization on carbon ionic liquid electrode (CILE) with a conductive hydrophobic ionic liquid, 1-butyl pyridinium hexafluophosphate ([BuPy][PF₆]) as binder for the first time. A pair of reversible peaks is exhibited on GOx/CILE by cyclic voltammetry. The peak-to-peak potential separation (ΔE_P) of immobilized GOx is 0.056 V in 0.067 M phosphate buffer solution (pH 6.98) with scan rate of 0.1 V/s. The average surface coverage and the apparent Michaelis–Menten constant are 6.69 × 10⁻¹¹ mol·cm⁻² and 2.47 μM. GOx/CILE shows excellent electrocatalytic activity towards glucose determination in the range of 0.1–800 μM with detection limit of 0.03 μM (S/N = 3). The biosensor has been successfully applied to the determination of glucose in human plasma with the average recoveries between 95.0% and 102.5% for three times determination. The direct electrochemistry of GOx on CILE is achieved without the help of any supporting film or any electron mediator. GOx/CILE is inexpensive, stable, repeatable and easy to be fabricated.     

基于碳量子点修饰硅胶荧光法测定塑料制品中的双酚A

制备了碳量子点修饰的硅胶SiO2@CDs.在盐酸介质中KBrO3能够氧化碳量子点使其荧光发射峰减弱,而双酚A(BPA)对此氧化猝灭有明显抑制作用,据此建立了荧光法测定痕量双酚A的新方法,线性范围是20~500μg·L-1,检出限3σ为5.2μg·L-1.本文作者将该方法成功用于塑料制品中双酚A的测定,回收率在95%~104%之间.     

Fabrication of a new electrochemiluminescent sensor for fentanyl citrate based on glassy carbon microspheres and ionic liquid composite paste electrode

Due to the high performance of glassy carbon in the aspects of mechanical strength, electrical conductivity and high corrosion resistance, etc., glassy carbon has been widely used in the electrochemistry. A new form of glassy carbon, glassy carbon microsphere, was utilized to couple with ionic liquid in preparing a new electrochemiluminescent platform for Ru(bpy)₃Cl₂. Room temperature ionic liquid has been proposed to be very interesting and efficient pasting binder to replace the non conductive organic binders for the fabrication of composite paste electrode. Attributed to the special characteristics of glassy carbon microspheres and room temperature ionic liquid [N-octylpyridium tetrafluoroborate (OPFP)], this new electrochemiluminescent sensor exhibited excellent electrochemiluminescent performance in Ru(bpy)₃²⁺ solution. We first found that fentanyl citrate could increase the ECL of Ru(bpy)₃²⁺, hence an ECL approach was developed for the determination of fentanyl citrate based on this glassy carbon microspheres based electrochemiluminescent platform with high sensitivity. Under the optimized conditions, the enhanced electrochemiluminescent intensity versus fentanyl citrate concentration was linear in the range of 1.0 × 10⁻⁸ to 1.0 × 10⁻⁴ mol L⁻¹ with a detection limit of 8.5 × 10⁻⁹ mol L⁻¹, and the relative standard deviation for 1.0 × 10⁻⁶ mol L⁻¹ fentanyl citrate was 1.90% (n = 10). This protocol has extended the application scopes of glassy carbon material and promoted the application of glassy carbon microspheres in electroanalysis.     

萘乙酸在多壁碳纳米管-离子液体复合修饰电极上的电催化氧化及电分析方法

运用循环伏安法(CV),计时库仑法(CC),计时电流法(CA)研究了萘乙酸(NAA)在玻碳电极(GCE),多壁碳纳米管修饰玻碳电极(MWCNTs/GCE)和多壁碳纳米管-离子液体修饰玻碳电极(MWCNTs-IL/GCE)上的电化学行为及电化学动力学性质.实验结果表明,NAA在GCE电极上于1.00V附近有一不可逆氧化峰...     

Electrochemical behavior and differential pulse voltammetric determination of paracetamol at a carbon ionic liquid electrode

The electrochemical behavior of paracetamol in 0.1 M acetate buffer solution (pH 4.6) was investigated at a traditional carbon paste electrode (TCPE) and a carbon ionic liquid electrode (CILE) fabricated by replacing nonconductive organic binders with a conductive hydrophobic room temperature ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate (BmimPF₆). The results showed that the CILE exhibited better reversibility for the electrochemical redox of paracetamol. The oxidation potential of paracetamol at the CILE is +0.462 V, which is approximately 232 mV lower than that at the TCPE; the oxidation peak current response is nine times higher than that at the TCPE. The differential pulse voltammetric determination of paracetamol at the CILE was established based on this behavior. After optimizing several important parameters controlling the performance of paracetamol at the CILE, the oxidation peak current versus paracetamol concentration at the CILE showed linearity in the range from 1.0 μM to 2.0 mM (R ²  = 0.9992) with a detection limit of 0.3 μM (S/N = 3). The method has been applied to the determination of paracetamol in tablets and urine samples and the average recovery of paracetamol was 98.5% and 99.3%, respectively. The proposed CILE showed good sensitivity and reproducible response without influence of interferents commonly existing in pharmaceutical and urine samples. Figure CV curves of paracetamol illustrate the enhanced electrochemical behavior of paracetamol at the CILE (b), which forms the basis for the differential pulse voltammetric determination of paracetamol     

Sensitive detection of endocrine disrupters using ionic liquid--single walled carbon nanotubes modified screen-printed based biosensors

Simple and low cost biosensor based on screen-printed electrode for sensitive detection of some alkylphenols was developed, by entrapment of HRP in a nanocomposite gel based on single-walled carbon nanotubes (SWCNTs) and 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF₆]) ionic liquid. Raman and FTIR spectroscopy, CV and EIS studies demonstrate the interaction between SWCNTs and ionic liquid. The nanocomposite gel, SWCNT-[BMIM][PF₆] provides to the modified sensor a considerable enhanced electrocatalytic activity toward hydrogen peroxide reduction. The HRP based biosensor exhibits high sensitivity and good stability, allowing a detection of the alkylphenols at an applied potential of −0.2 V vs. Ag/AgCl, in linear range from 5.5 to 97.7 μM for 4-t-octylphenol and respectively, between 5.5 and 140 μM for 4-n-nonylphenol, with a response time of about 5 s. The detection limit was 1.1 μM for 4-t-octylphenol, and respectively 0.4 μM for 4-n-nonylphenol (S/N = 3).