Electrochemical determination of dopamine and ascorbic acid at a novel gold nanoparticles distributed poly(4-aminothiophenol) modified electrode

A modified electrode is fabricated by embedding gold nanoparticles into a layer of electroactive polymer, poly(4-aminothiophenol) (PAT) on the surface of glassy carbon (GC) electrode. Cyclic voltammetry (CV) is performed to deposit PAT and concomitantly deposit Au nanoparticles. Field emission transmission electron microscopic image of the modified electrode, PAT-Au_nano-ME, indicates the presence of uniformly distributed Au nanoparticles having the sizes of 8-10 nm. Electrochemical behavior of the PAT-Au_nano-ME towards detection of ascorbic acid (AA) and dopamine (DA) is studied using CV. Electrocatalytic determination of DA in the presence of fixed concentration of AA and vice versa, are studied using differential pulse voltammetry (DPV). PAT-Au_nano-ME exhibits two well defined anodic peaks at the potential of 75 and 400 mV for the oxidation of AA and DA, respectively with a potential difference of 325 mV. Further, the simultaneous determination of AA and DA is studied by varying the concentration of AA and DA. PAT-Au_nano-ME exhibits selectivity and sensitivity for the simultaneous determination of AA and DA without fouling by the oxidation products of AA or DA. PAT and Au nanoparticles provide synergic influence on the accurate electrochemical determination of AA or DA from a mixture having any one of the component (AA or DA) in excess. The practical analytical utilities of the PAT-Au_nano-ME are demonstrated by the determination of DA and AA in dopamine hydrochloride injection and human blood serum samples.     

Electrocatalytic response of dopamine at a dl-homocysteine self-assembled gold electrode

The gold electrode self-assembled with the homocysteine monolayer (Hcy/Au) is demonstrated to catalyze the electrochemical response of dopamine (DA) by cyclic voltammetry. A pair of well-defined redox waves was obtained and the calculated standard rate constant (k_s) is 2.1×10⁻² cm/s at the self-assembled electrode. The reduction peak of DA can be used to determine the concentration of DA in presence of ascorbic acid (AA) owing to the Hcy/Au also catalyzing the electrochemical oxidation of AA.     

OH functionalized Multi-Walled Carbon Nanotube modified electrode as electrochemical sensor for the detection of Aceclofenac

ABSTRACT

The rapid electrochemical determination of Aceclofenac (ACF) has been employed by cyclic voltammetry (CV), differential pulse voltammetry (DPV) using developed OH-functionalised multiwalled carbon nanotube carbon paste electrode (OH-MWCNT/CPE). Modified electrode was characterised by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDAX), X-ray diffraction spectroscopy (XRD), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The ACF exhibits two oxidation peaks at +0.4 V, +0.66 V and one reduction peak at +0.3 V. The active surface area of the bare carbon paste electrode (BCPE) and modified electrode have been characterised by using K₃[Fe(CN)₆] solution containing 0.1 M KCl. In DPV mode, variation of ACF gave the limit of detection (LOD = 3s/m) 0.246 μM over the concentration range 1.0 to 190.0 μM (R² = 0.9994). The developed electrode has good stability, reproducibility and could be successfully validated for the detection of ACF in pharmaceutical samples and biological fluids.     

Electrochemical behavior of some triazine derivatives at glassy carbon electrode in non-aqueous media

Electroreduction of 4-amino-6-methyl-3-thio-1,2,4-triazine-5-one (I), 6-methyl-3-thio-1,2,4-triazine-5-one (II), and 2,4-dimethoxy-6-methyl-1,3,5-triazine (III) in dimethylformamide was investigated. Electrochemical techniques including differential pulse voltammetry (DPV), cyclic voltammetry (CV), chronoamperometry, and coulometry were employed to study the mechanism of the electrode process. From the analysis of the voltammetric and spectroscopic experiments a mechanism was proposed for the electroreduction of thio-triazine and triazine compounds. Compounds I and II having thiol groups exhibited similar redox behavior. Both compounds displayed two cathodic peaks, whereas the third compound (III), with no thiol group, showed only one cathodic peak in the same potential range as the second peak of compounds I and II.The results of this study show that in the former wave, the one electron reduction of thiol led to a dimer (disulfide) species and in the latter, the triazine ring was reduced in a two-electron process. The effects of various physical and electrochemical parameters were studied and the electrochemical behavior of the monomers was reported as a function of these parameters. A completely irreversible behavior was observed from cyclic voltammograms obtained under different conditions. Furthermore, in this study some numerical constants, such as diffusion constant, transfer coefficient, and rate constant of coupled chemical reaction were determined.     

聚甲基蓝修饰电极的制备及对多巴胺的测定

研究了聚甲基蓝修饰电极的制备及其多巴胺在聚甲基蓝修饰电极上的循环伏安特性,建立了循环伏安法测定多巴胺的新方法。在pH7.0磷酸盐缓冲溶液中,峰电流与多巴胺浓度在8.0×10-7～5.0×10-4mol L范围内呈良好的线性关系,检出限为5.0×10-8mol L。已用于药剂中多巴胺的测定。     

多巴胺在牛磺酸修饰玻碳电极上的电化学行为及其分析应用

采用电化学聚合法制备了牛磺酸修饰玻碳电极,研究了多巴胺在聚牛磺酸修饰电极上的电化学行为,建立了测定痕量多巴胺的新方法.在pH 7.2的磷酸盐缓冲溶液中,多巴胺在修饰电极上产生一对灵敏的氧化还原峰,采用差分脉冲伏安法测定,其氧化峰电流与多巴胺浓度在8.0×10-8～1.0×10-4 mol/L范围内呈良好的线性关系,检出限为1.0×10-8 mol/L.     

维生素B6在纳米金/石墨烯修饰电极上的电化学行为

将金纳米粒子电沉积在石墨烯修饰的玻碳电极表面,研究了维生素B6(VB6)在该修饰电极上的电化学行为。扫描电镜用于该修饰电极组装过程的形貌表征。实验结果表明:VB6在此修饰电极上出现一个良好的氧化峰,在最佳实验条件下,其氧化峰电流与VB6浓度在5.0×10-8～2.0×10-5 mol/L范围内呈线性关系,其线性回归方程为I(μA)=0.5697c(μmol/L)+0.06275,R=0.9992,检出限为2.0×10-8 mol/L(S/N=3)。一些常见的干扰物质如抗坏血酸不干扰VB6的检测。方法已用于片剂中VB6的含量的检测。     

Electrochemical oxidation of cisatracurium on carbon paste electrode and its analytical applications

The electrochemical oxidation of cisatracurium was investigated by cyclic voltammetry and differential pulse voltammetry at a carbon paste electrode and the experimental parameters have been optimized in order to obtain the optimum analytical signal. A differential pulse voltammetric method with carbon paste electrode is described for the determination of cisatracurium with detection limit of 0.38 μg/ml and quantitation limit of 1.26 μg/ml. The proposed method was applied to determine the content of cisatracurium in human urine and human serum, obtaining accurate and precise results.     

多巴胺在咖啡酸修饰电极上的电化学行为

研究了咖啡酸修饰玻碳电极的制备及其电化学性质,测定了电极反应的动力学常数。实验结果表明,在pH7.0的磷酸盐缓冲溶液中,多巴胺(DA)在该修饰电极上产生一灵敏的氧化峰,峰电流与DA浓度在5.0×10-6～1.0×10-4mol/L范围内良好线性关系,检出限为9.0×10-7mol/L。该修饰膜对DA有增敏作用,可望用于DA的测定。     

磷酸可待因在Nafion修饰玻碳电极上的伏安行为研究及测定

用循环伏安法和微分脉冲吸附伏安法对磷酸可待因在Nafion修饰玻碳电极上的伏安行为进行了研究。结果表明在 0 .1mol/LHCl底液中 ,磷酸可待因在 + 1 .0 6V处 (vs.SCE)产生一良好的氧化峰 ,磷酸可待因浓度在 5 .0× 1 0 - 7～2 .5× 1 0 - 5mol/L范围内与峰电流呈线性关系 ,检出限为 1 .3× 1 0 - 7mol/L。并分别对其单方药和复方药制剂进行了测定     

聚L-酪氨酸修饰电极的制备及对多巴胺的测定

用循环伏安法制备了聚L 酪氨酸修饰玻碳电极,研究了多巴胺在聚L 酪氨酸修饰电极上的电化学行为,建立了循环伏安法测定痕量多巴胺的新方法。多巴胺在pH7.0的磷酸盐缓冲溶液中,在聚L 酪氨酸修饰玻碳电极上产生一对灵敏的氧化还原峰,峰电位分别为Epa=189mV,Epc=131mV。循环伏安法测定多巴胺的线性范围为1.0×10-3～1.0×10-8mol/L,检出限:1.0×10-9mol/L。方法可用于药剂中多巴胺的测定。     

Electrochemical behaviour of triclosan at a screen-printed carbon electrode and its voltammetric determination in toothpaste and mouthrinse products

Cyclic voltammetry was used to investigate the electrochemical behaviour of triclosan (2,2,4′-trichloro-2′-hydroxydiphenyl ether) at a screen-printed carbon electrode (SPCE). It was found that a single anodic peak occurred over the pH range 6.0–12.0; this peak was considered to result from an irreversible oxidation reaction at the phenolic moiety. A plot of E_p versus pH was constructed and from the break point a pK_a value of 7.9 was obtained, thus agreeing with the literature value. Detailed voltammetric studies were performed at pH 10, where the analyte exists as an anion. It was demonstrated that, at an initial potential of 0 V, the anion underwent electrosorption prior to electrochemical oxidation. The oxidation reaction appeared to involve a one-electron transfer, as deduced from a calculated n_a value of 0.5; the same value was obtained at pH 7.0. In contrast to triclosan, triclosan monophosphate was found to be electrochemically inactive when subjected to voltammetry under the stated conditions.

The electrochemical oxidation of triclosan at a SPCE was exploited for its determination (0.3%) in commercial toothpaste and mouthrinse products using differential pulse voltammetry. The recovery and precision data indicated that this approach may have application in routine quality control analysis.     

头孢克洛降解产物的电化学行为和测定

研究了在0.5mol/LNaOH溶液中,头孢克洛碱性降解产物在汞膜电极上的电化学为,并依此建立了头孢克洛的微分脉冲伏安测定法。头孢克洛碱性降解产物于～-0.85V(vs.Ag/AgCl)处出一灵敏的阴极还原峰,用循环伏安法、线性扫描极谱法、微分脉冲伏安法等手段研究了其电化学行为和机理。实验表明:头孢克洛降解产物在汞膜电极上具有明显的吸附性,电化学反应的电子转移数为2。伏安峰高与头孢克洛的浓度在1.0×10-8～5.0×10-6mol/L范围内有良好的线性关系。方法的检出限为5.0×10-9mol/L,方法可用于药品欣可诺颗粒剂中头孢克洛的测定。     

Voltammetric behavior and determination of bismuth on sodium humate modified carbon paste electrode

The preconcentration and voltammetric behavior of Bi^III on a sodium humate modified carbon paste electrode was studied by means of cyclic voltammetry (CV) and differential pulse stripping voltammetry (DPSV). The proposed measurement involves an initial nonelectrolytic preconcentration step in which Bi^III is complexed by the surface modifier in a solution of 0.05 M KNO₃-0.0106 M HNO₃ (pH 2.0) and a subsequent electrochemical scan step in which the preconcentrated Bi^III was reduced and then oxidized promptly in supporting electrolyte of 0.5 M HNO₃. The resulting DPSV anodic current was proportional to the concentration of Bi^III ion over the range of 4.78 × 10⁻⁸–1.44 × 10⁻⁵ M. The detection limit was 4.78 × 10⁻⁸ M. The proposed method was used to determine bismuth in various samples. Various factors affecting the electrode behavior were also investigated at the same time.     

Simultaneous voltammetric detection of ascorbic acid, dopamine and uric acid using a pyrolytic graphite electrode modified into dopamine solution

Pyrolytic graphite electrodes (PGE) were modified into dopamine solutions using phosphate buffer solutions, pH 10 and 6.5, as supporting electrolyte. The modification process involved a previous anodization of the working electrode at +1.5 V into 0.1 mol L⁻¹ NaOH followed by other anodization step, in the same experimental conditions, into dopamine (DA) solutions. pH of the supporting electrolyte performed an important role in the production of a superficial melanin polymeric film, which permitted the simultaneous detection of ascorbic acid (AA), (DA) and uric acid (UA), ΔE_AA-DA = 222 mV; ΔE_AA-UA = 360 mV and ΔE_DA-UA = 138 mV, avoiding the superficial poisoning effects. The calculated detection limits were: 1.4 × 10⁻⁶ mol L⁻¹ for uric acid, 1.3 × 10⁻⁵ mol L⁻¹ for ascorbic acid and 1.1 × 10⁻⁷ mol L⁻¹ for dopamine, with sensitivities of (7.7 ± 0.5), (0.061 ± 0.001) and (9.5 ± 0.05) A mol⁻¹ cm⁻², respectively, with no mutual interference. Uric acid was determined in urine, blood and serum human samples after dilution in phosphate buffer and no additional sample pre-treatment was necessary. The concentration of uric acid in urine was higher than the values found in blood and serum and the recovery tests (92-102%) indicated that no matrix effects were observed.     

Electrochemical behavior of mesoionic sydnone derivatives at wax-impregnated carbon paste electrode

The-N=N-moiety in the mesoionic 3-phenyl sydnone and its derivatives like tolyl sydnones and anisyl sydnones undergo two-electron irreversible electrochemical reduction in Britton-Robinson (BR) buffer at wax-impregnated carbon paste electrodes. Infrared, nuclear magnetic resonance, and mass-spectral data, used to characterize the reduced product, confirm the proposed mechanism. The pasting liquid at the surface of the electrode is found to decrease the electron-transfer rate and cause a higher overpotential compared to homogeneous electrodes. The influence of variation of pH on the peak current and peak potentials is studied in the acidic range. The cathodic peak shifts to more negative potentials with increase in pH, indicating the involvement of proton in the reduction process. This could be a new method of preparation of 2,4-dihydro-3-substituted 1,2,3-oxadiazole-5-one. The substituent effect and the effect of variation of scan rate, concentration, and temperature on peak currents and peak potentials is discussed. The cathodic shift in various organic co-solvents (methanol, acetonitrile, DMF, DMSO) using BRB as the supporting electrolyte is examined. Published in Russian in Elektrokhimiya, 2006, Vol. 42; No. 7, pp. 862–868. The text was submitted by the authors in English.     

Electrocatalytic response of norepinephrine at a thiolactic acid self-assembled gold electrode

The thiolactic acid (TLA) self-assembled monolayer modified gold electrode (TLA/Au) is demonstrated to catalyze the electrochemical response of norepinephrine (NE) by cyclic voltammetry. A pair of well-defined redox waves were obtained and the calculated standard rate constant (k_s) is 5.11×10⁻³ cm s⁻¹ at the self-assembled electrode. The electrode reaction is a pseudo-reversible process. The peak current and the concentration of NE are a linear relationship in the range of 4.0×10⁻⁵–2.0×10⁻³ mol l⁻¹. The detection limit is 2.0×10⁻⁶ mol l⁻¹. By ac impedance spectroscopy the apparent electron transfer rate constant (k_app) of Fe(CN)³⁻/Fe(CN)⁴⁻ at the TLA/Au electrode was obtained as 2.5×10⁻⁵ cm s⁻¹.     

聚磺胺嘧啶修饰电极伏安法测定对乙酰氨基酚

利用循环伏安法制备了聚磺胺嘧啶修饰电极, 研究了对乙酰氨基酚在该修饰电极上的电化学行为. 该电极对对乙酰氨基酚有较强的电催化作用. 在pH 9.0的PBS缓冲溶液中, 用循环伏安法和差分脉冲伏安法在该电极上测定了对乙酰氨基酚, 其线性范围分别为4.0×10-6～3.0×10-4 mol/L和2.0×10-7～1.0×10-5 mol/L, 检出限分别为9.0×10-7 mol/L和8.0×10-8 mol/L.     

多巴胺在DTNB自组装膜上的电催化研究

在金电极表面制备了DTNB(5,5′ Di thiobis(2 nitrobenzoicacid))自组装单分子层膜(DTNB/AuSAM)。多巴胺在DTNB自组装膜上有一对可逆性良好的氧化还原峰,其氧化峰电流与多巴胺的浓度在5.0×10-6mol/L～1.0×10-4mol/L的范围内呈线性关系,检出限为1.0×10-6mol/L。在pH3.5的缓冲溶液中,在DTNB自组装膜上多巴胺和抗坏血酸的电化学响应可以明显区分,氧化峰电位分离达276mV。可用于抗坏血酸存在下多巴胺的检测。测定了盐酸多巴胺注射液中多巴胺的含量,其平均回收率为104%。