Simultaneous determination of dopamine, ascorbic acid and uric acid at poly (Evans Blue) modified glassy carbon electrode

A sensitive and selective electrochemical method for the determination of dopamine using an Evans Blue polymer film modified on glassy carbon electrode was developed. The Evans blue polymer film modified electrode shows excellent electrocatalytic activity toward the oxidation of dopamine in phosphate buffer solution (pH 4.5). The linear range of 1.0 x 10(-6)-3.0 x 10(-5) M and detection limit of 2.5 x 10(-7) M were observed in pH 4.5 phosphate buffer solutions. The interference studies showed that the modified electrode exhibits excellent selectivity in the presence of large excess of ascorbic acid and uric acid. The separation of the oxidation peak potentials for dopamine-ascorbic acid and dopamine-uric acid were about 182 mV and 180 mV, respectively. The differences are large enough to determine AA, DA and UA individually and simultaneously. This work provides a simple and easy approach to selectively detect dopamine in the presence of ascorbic acid and uric acid in physiological samples.     

Preparation of aminylferrocene/nanogold modified glassy carbon electrode and its electrocatalysis on dopamine

Aminylferrocene(FcAI)-Nanogold(NG) modified glassy carbon electrode (FcAI/NG/GCE) was prepared by the Au-N bond between Au and FcAI. Electrochemical impedance spectroscopy (EIS) was employed to study the surface of the modified electrode. The electrochemical behavior of dopamine (DA) on the modified electrode was investigated and it was found that the modified electrode had an obvious electrocatalytic effect on DA. Compared with a bare GCE, the modified electrode exhibited an apparent shift of the oxidation peak potential in the negative potential direction and a marked enhancement in the current response for DA. We investigated the determination of DA on the modified electrode by differential pulse voltammetry (DPV). Linear calibration curve was obtained in the range of 7.0 x 10(-7) mol/L to 6x10(-4) mol/L of DA in 0.1 mol/L phosphate buffer solution (pH = 7.0) with a correlation coefficient of 0.9989. The detection limit (S/N = 3) of DA was estimated to be 1.0 x 10(-7) mol/L. Especially, by using the modified electrode, we can separate the oxidation peaks of ascorbic acid (AA) and DA in the PBS and it was satisfactory for the determination of DA with the interference of AA.     

柠檬酸修饰电极对抗坏血酸、多巴胺和尿酸的同时检测

研究柠檬酸(CA)修饰玻碳电极(CA/GC)在抗坏血酸(AA)、多巴胺(DA)和尿酸(UA)混合体系中的循环伏安(CV)行为.结果表明,AA、DA和UA在CA/GC电极上氧化峰电流增大,且三者氧化峰电位明显分离(ΔEp(DA,AA)=170 mV,ΔEp(DA,UA)=130 mV,ΔEp(AA,UA)=300 mV).据此,可同时检测AA、DA和UA.在优化的实验条件下,AA、DA和UA的氧化峰电流与其浓度分别在2.0×10-6～1.5×10-3mol.L-1,6.0×10-7～1.0×10-3mol.L-1和6.0×10-7～1.0×10-3mol.L-1范围内呈线性关系.该电极重现性好,可用于盐酸多巴胺针剂DA、VC片剂AA及人体尿液UA的测定.     

Selective Detection of Uric Acid in the Presence of Ascorbic Acid and Dopamine Using Polymerized Luminol Film Modified Glassy Carbon Electrode

Electrochemically polymerized luminol film on a glassy carbon electrode (GCE) surface has been used as a sensor for selective detection of uric acid (UA) in the presence of ascorbic acid (AA) and dopamine (DA). Cyclic voltammetry was used to evaluate the electrochemical properties of the poly(luminol) film modified electrode. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) have been used for surface characterizations. The bare GCE failed to distinguish the oxidation peaks of AA, DA and UA in phosphate buffer solution (pH 7.0), while the poly(luminol) modified electrode could separate them efficiently. In differential pulse voltammetric (DPV) measurements, the modified GCE could separate AA and DA signals from UA, allowing the selective determination of UA. Using DPV, the linear range (3.0×10^?5 to 1.0×10^?3 M) and the detection limit (2.0×10^?6 M) were estimated for measurement of UA in physiological condition. The applicability of the prepared electrode was demonstrated by measuring UA in human urine samples.     

Silver Doped Poly(L‐valine) Modified Glassy Carbon Electrode for the Simultaneous Determination of Uric Acid,Ascorbic Acid and Dopamine

In this paper, a silver doped poly(L ‐valine) (Ag‐PLV) modified glassy carbon electrode (GCE) was fabricated through electrochemical immobilization and was used to electrochemically detect uric acid (UA), dopamine (DA) and ascorbic acid (AA) by linear sweep voltammetry. In pH 4.0 PBS, at a scan rate of 100 mV/s, the modified electrode gave three separated oxidation peaks at 591 mV, 399 mV and 161 mV for UA, DA and AA, respectively. The peak potential differences were 238 mV and 192 mV. The electrochemical behaviors of them at the modified electrode were explored in detail with cyclic voltammetry. Under the optimum conditions, the linear ranges were 3.0×10^?7 to 1.0×10^?5 M for UA, 5.0×10^?7 to 1.0×10^?5 M for DA and 1.0×10^?5 to 1.0×10^?3 M for AA, respectively. The method was successfully applied for simultaneous determination of UA, DA and AA in human urine samples.     

Simultaneous determination of ascorbic acid, dopamine, uric acid and xanthine using a nanostructured polymer film modified electrode

This paper describes the simultaneous determination of ascorbic acid (AA), dopamine (DA), uric acid (UA) and xanthine (XN) using an ultrathin electropolymerized film of 2-amino-1,3,4-thiadiazole (p-ATD) modified glassy carbon (GC) electrode in 0.20 M phosphate buffer solution (pH 5.0). Bare GC electrode failed to resolve the voltammetric signals of AA, DA, UA and XN in a mixture. On the other hand, the p-ATD modified electrode separated the voltammetric signals of AA, DA, UA and XN with potential differences of 110, 152 and 392 mV between AA-DA, DA-UA and UA-XN, respectively and also enhanced their oxidation peak currents. The modified electrode could sense 5 μM DA and 10 μM each UA and XN even in the presence of 200 μM AA. The oxidation currents were increased from 30 to 300 μM for AA, 5 to 50 μM for DA and 10 to 100 μM for each UA and XN, and the lowest detection limit was found to be 2.01, 0.33, 0.19 and 0.59 μM for AA, DA, UA and XN, respectively (S/N = 3). The practical application of the present modified electrode was demonstrated by the determination of AA, UA and XN in human urine samples.     

Electrochemical determination of serotonin and the competitive adsorption with dopamine at 5,5-ditetradecyl-2-(2-trimethylammonioethyl)-1,3-dioxane bromide lipid film modified by glassy carbon electrode.

A novel and effective approach to sensitively determine serotonin, known as 5-hydroxytryptamine (5-HT), has been proposed based on a 5,5-ditetradecyl-2-(2-trimethylammonioethyl)-1,3-dioxane bromide (DTDB) self-assembled lipid bilayer membrane modified glassy carbon electrode (DTDB/GCE). A DTDB/GCE shows the strong electrocatalysis for the oxidation of 5-HT, with the peak potential shifted to less positive value of 0.376 V vs. SCE, and effectively eliminates the interference from ascorbic acid (AA), even in the presence of 100-fold concentration of AA. Differential pulse voltammetry (DPV) gave a linear current for 5-HT from 2.0 x 10(-7) to 1.0 x 10(-5) M. At the DTDB/GCE, the oxidation of 5-HT was controlled by the adsorption process; for 5-HT coexisting with DA, the competitive adsorption was observed.     

Detection of Uric Acid in the Presence of Dopamine and High Concentration of Ascorbic Acid Using PDDA Modified Graphite Electrode

The properties of graphite electrode (Gr) modified with poly(diallyl dimethyl ammonium chloride) (PDDA) for the detection of uric acid (UA) in the presence of dopamine (DA) and high concentration of ascorbic acid (AA) have been investigated by cyclic voltammetry, differential pulse voltammetry and chronoamperometry. The polymer modified graphite electrode was prepared by a very simple method just by immersing the graphite electrode in PDDA solution for 20 minutes. The PDDA/Gr modified electrode displayed excellent electrocatalytic activity towards the oxidation of UA, DA and AA compared to that at the bare graphite electrode. The electrochemical oxidation signals of UA, DA and AA are well resolved into three distinct peaks with peak potential separations of 220 mV, 168 mV and 387 mV between AA‐DA, DA‐UA and AA‐UA respectively in cyclic voltammetry studies and the corresponding peak potential separations are 230 mV, 130 mV and 354 mV respectively in differential pulse voltammetry. The lowest detection limits obtained for UA, DA and AA were 1×10^?7 M, 2×10^?7 M and 800×10^?9 M respectively. The PDDA/Gr electrode efficiently eliminated the interference of DA and a high concentration of AA in the determination of UA with good selectivity, sensitivity and reproducibility. The modified electrode was also successfully applied for simultaneous determination of UA, DA and AA in their ternary mixture.     

Covalent modification of glassy carbon electrodes with beta-alanine for voltammetric separation of dopamine and ascorbic acid.

beta-Alanine was covalently grafted on a glassy carbon electrode (GCE) by amine cation radical formation in the electrooxidation process of the amino-containing compound. X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry (CV) proved the immobilization of beta-alanine monolayer on GCE. The electrode shows strong electrocatalytic functions to dopamine (DA) and ascorbic acid (AA), reducing the overpotentials by 0.20 V and 0.23 V, respectively. Due to its different catalytic effects toward DA and AA, the modified electrode resolved the overlapping voltammetric responses of DA and AA into two well-defined voltammetric peaks by CV or differential pulse voltammetry (DPV), which can be used for the simultaneous determination of these species in a mixture. The catalytic peak current obtained from DPV was linearly related to DA and AA concentrations in the ranges of 4.0 x 10(-6)-5.0 x 10(-4) mol/L and 2.0 x 10(-5)-6.0 x 10(-3) mol/L with correlation coefficients of 0.997 and 0.995, respectively. The detection limits (3 sigma) for DA and AA were 2.4 x 10(-6) mol/L and 1.2 x 10(-5) mol/L, respectively. The electrode shows good sensitivity, selectivity and stability, and has been applied to the determination of DA and AA simultaneously in samples with satisfactory results.     

Electrocatalytical Oxidation and Determination of Dopamine at Redox Polymer/Nafion Modified Electrodes

ABSTRACT

The modified glassy carbon electrodes prepared by simultaneously covering with [Os(bpy)₂(PVP)₁₀Cl]⁺ redox polymer and Nafion film exhibited excellent electrocatalytic activity for the oxidation of dopamine (DA). Dual linear regions between 1.0x10^?8-1.8x10^?5 M and 1.8x10^?5-4.0x10^?4 M with correlation coefficients of 0.998 and 0.995, respectively, were obtained for log-log plots of catalytic current versus DA concentration. The detection limit for DA determination was ca. 5 nM with 3σ. The dual-film modified electrodes eliminated efficiently the interference from AA presence in a 1000-fold concentration ratio and showed excellent reproducibility for the determination of DA. The modified electrodes have been used to determine DA concentration with both cyclic voltammetric and chronoamperometric techniques. Electrocatalytic kinetics have been studied using a rotating disk electrode. Both the addition of Nafion film and an increase in DA concentration resulted in a decrease in the electrocatalytic rate constant. An apparent Michaelis-Menten constant of 1.3 mM and maximum catalytic current of 88μA were evaluated from the chronoamperometric measurements.     

Selective determination of dopamine in the presence of ascorbic acid at an over-oxidized poly(N-acetylaniline) electrode.

An over-oxidized poly(N-acetylaniline) (PNAANI)/GCE was used to determine dopamine (DA) in a large excess of ascorbic acid (AA) by differential pulse voltammetry. A linear relation between Ip and DA concentration was found over the range 5.0 x 10(-7) to 2.0 x 10(-5) M. The detection limit was 1.68 x 10(-8) M for S/N = 3 and 400 microM AA did not interfere with the DA determination. The high sensitivity was due to accumulation and selectivity was due to charge discrimination. The mechanism of selective determination of DA at over-oxidized PNAANI/GCE was also proposed.     

Differential pulse voltammetric determination of dopamine with the coexistence of ascorbic acid on boron-doped diamond surface

Electrochemical determination of dopamine (DA) in the presence of ascorbic acid (AA) was achieved on boron-doped diamond (BDD) film electrode by differential pulse voltammetry. The experimental results indicated that the oxidative peaks of DA and AA could be separated completely on anodically-treated (BDD) electrode without further modification, although these two peaks can not be separated on glassy carbon electrode. The peak separation of DA and AA was developed to be 0.44 V. High sensitivity was obtained to determine DA selectively with the coexisting of a large excess of AA in acidic media by DPV. The detection limit of DA was achieved to be 1.1 × 10^-6 M in the presence of AA with the concentration of 200 times more than DA. This technique was also applied to the determination of DA in real samples.      

Catalytic Oxidation of Ascorbic Acid at a Polyhistidine Modified Electrode and Its Application to the Voltammetric Resolution of Ascorbic Acid and Dopamine

Abstract

A new polymer (polyhistidine) modified electrode has been fabricated and was applied to the catalytic oxidation of ascorbic acid (AA), reducing the overpotential by 400 mV. The catalytic rate constant of the modified electrode for the oxidation of AA was determined using a rotating electrode. The catalytic current was linearly dependent on the ascorbic acid concentration between 5×10^?5 and 2×10^?3 M. The catalytic effect on the AA resulted in the separation of the overlapping voltammograms of AA and dopamine (DA) in a mixture. This allowed the determination of AA in the presence of DA. The electrode was rather stable even after several months; a reproducible response of AA was obtained.     

Covalent modification of glassy carbon electrode with glutamic acid for simultaneous determination of uric acid and ascorbic acid

A novel covalently modified glassy carbon electrode with glutamic acid has been fabricated via an electrochemical oxidation procedure and was applied to the catalytic oxidation of uric acid (UA) and ascorbic acid (AA), reducing the overpotentials by about 0.2 V and 0.3 V, respectively. Based on its strong catalytic function toward the oxidation of UA and AA, the modified electrode resolved the overlapping voltammetric response of UA and AA into two well-defined voltammetric peaks with both cyclic voltammetry (CV) and differential pulse voltammetry (DPV), which can be used for the simultaneous determination of these species in a mixture. The catalytic peak current obtained from DPV was linearly dependent on the UA and AA concentration in the range 2 x 10(-6)-4 x 10(-4) mol L-1 and 1.0 x 10(-6)-4 x 10(-4) mol L-1 with correlation coefficients of 0.996 and 0.997, respectively. The detection limits (3 delta) for UA and AA were 1.1 x 10(-6) mol L-1 and 9.2 x 10(-7) mol L-1, respectively. The modified electrode shows good sensitivity, selectivity and stability, and has been applied to the determination of UA and AA simultaneously in human urine samples with satisfactory results.     

Electrochemical determination of dopamine using a poly(2-picolinic acid) modified glassy carbon electrode

A poly(2-picolinic acid) chemically modified electrode (CME) for the determination of dopamine (DA) by cyclic voltammetry is described. Compared with a bare glassy carbon electrode, the CME exhibits a 200 mV shift of the oxidation potential of DA in the cathodic direction and a marked enhancement of the current response. In pH 7.0 buffer solution, a linear calibration graph is obtained over the range from 2.5 x 10(-7) to 1.0 x 10(-5) mol dm-3 with a correlation coefficient of 0.998. The detection limit is 3.0 x 10(-8) mol dm-3. The modified electrode eliminated efficiently the interference from ascorbic acid (AA) when present in a 150-fold concentration ratio. It also showed excellent stability and reproducibility.     

聚伊文思蓝修饰电极对多巴胺和抗坏血酸的电分离及同时测定

研究多巴胺(DA)和抗坏血酸(AA)在聚伊文思蓝(Evans Blue)修饰电极上的伏安行为,建立差示脉冲伏安测定法.在pH4.5磷酸盐缓冲液中,聚伊文思蓝修饰电极对DA和AA有显著的增敏和电分离作用.DA和AA氧化峰电流与浓度分别在1.0×10-6~3.0×10-5mol/L和5.0×10-6~1.05×10-4mol/L范围内呈良好的线性关系,检测限分别为2.5×10-7mol/L和3.0×10-7mol/L.当DA与AA共存时,由该修饰电极检测的二者氧化峰电位差达184 mV,故可同时测定DA和AA,并有效消除其它组分对DA测定的干扰,已用于实际样品中DA和AA含量的测定,结果令人满意.     

Covalent modification of glassy carbon electrodes with glycine for voltammetric separation of dopamine and ascorbic acid

Glycine was covalently grafted on to a glassy carbon electrode (GCE) by amine cation radical formation in electrooxidation of the amino-containing compound. X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry proved the immobilization of glycine on the GCE. The modified electrode reduced the overpotentials of dopamine (DA) and ascorbic acid (AA) by approximately 0.15 V and 0.23 V, respectively, and resolved the overlapping voltammetric response of DA and AA into two well-defined voltammetric peaks in cyclic voltammetry (CV) or differential pulse voltammetry (DPV), unlike the unmodified GCE; this can be used for the simultaneous determination of these species in a mixture. The differential pulse peak current was linearly dependent on DA and AA concentration in the range 5 x 10(-6)-8 x 10(-4) mol L(-1) and 6 x 10(-5)-4 x 10(-3) mol L(-1), with correlation coefficients of 0.996 and 0.994, respectively. The detection limits (3delta) for DA and AA were 1.8 x 10(-6) mol L(-1) and 2.1 x 10(-5) mol L(-1), respectively. The modified electrode is very sensitive, selective and stable, and has been applied to the determination of DA and AA simultaneously in samples with satisfactory results.     

Electrochemical behavior of ascorbic acid at a 2,2'-[3,6-Dioxa-1,8-octanediylbis(nitriloethylidyne)]-bis-hydroquinone carbon paste electrode

Electrocatalytic oxidation of ascorbic acid (AA) at a carbon paste electrode, chemically modified 2,2'-[3,6-dioxa-1,8-octanediylbis(nitriloethylidyne)]-bis-hydroquinone, was thoroughly investigated. The results of cyclic voltammetry, double potential-step chronoamperometry, linear sweep voltammetry and differential pulse voltammetry (DPV) studies were used for the prediction of the mechanism of electrochemical oxidation of AA mediated with 2,2'-[3,6-dioxa-1,8-octanediylbis(nitriloethylidyne)]-bis-hydroquinone at the surface of the modified electrode. The diffusion coefficient (D = 2.45 x 10(-5) cm(2) s(-1)) and the kinetic parameters such as the electron transfer coefficient (alpha = 0.34) were also determined. The results of DPV using the 2,2'-[3,6-dioxa-1,8-octanediylbis(nitriloethylidyne)]-bis-hydroquinone-modified electrode were applied in a highly sensitive determination of AA in drug samples. A linear range of 3.0 x 10(-6) - 1.2 x 10(-4) M and the detection limit (3sigma) 3.8 x 10(-7) M were obtained for DPV determination of AA in buffered pH 7.00 solutions (0.1 M phosphate buffer).     

Ion-exchange voltammetry of dopamine at Nafion-coated glassy carbon electrodes: quantitative features of ion-exchange partition and reassessment on the oxidation mechanism of dopamine in the presence of excess ascorbic acid

The incorporation/exclusion features of dopamine (DA), ascorbic acid (AA) and uric acid (UA) are evaluated for Nafion (NA)-coated glassy carbon electrodes (GCE) of different thicknesses. The ion-exchange partition of DA(+) between the NA film and the sodium phosphate electrolyte is evaluated by determining the partition coefficient (k(D)) and the apparent diffusion coefficient (D(app)) in thick NA films which were 401 and 1.5 x 10(-9) cm(2) s(-1), respectively. The solution diffusion coefficient was found to be 6.0 x 10(-6) cm(2) s(-1). Also, the effect of NA loading and of the voltammetric timescale on DA voltammetry in the presence of excess AA is assessed, at physiologic like conditions. It is demonstrated that, although AA is excluded at the NA coating, a catalytic regeneration of DA, induced by AA, occurs at the interface NA film/electrolyte resulting from the diffusion of the o-quinone product of DA oxidation from the electrode surface to that interface. The interference of AA in the voltammetric signal of DA is eliminated using 18 microg mm(-2) NA films and v> or =0.5 V s(-1). Therefore, fast, selective and sensitive voltammetric analysis of DA at concentrations<100 microM in the presence of excess AA, e.g., 1 mM is achieved.     

Enhanced sensing of dopamine in the present of ascorbic acid based on graphene/poly(p-aminobenzoic acid) composite film

Graphene/p-aminobenzoic acid composite film modified glassy carbon electrode (Gr/p-ABA/GCE) was first employed for the sensitive determination of dopamine (DA). The electrochemical behavior of DA at the modified electrode was investigated by cyclic voltametry (CV), differential pulse voltametry (DPV) and amperometric curve. The oxidation peak currents of DA increased dramatically at Gr/p-ABA/GCE. The modified electrode was used to electrochemically detect dopamine (DA) in the presence of ascorbic acid (AA). The Gr/p-ABA composite film showed excellent electrocatalytic activity for the oxidation of DA in phosphate buffer solution (pH 6.5). The peak separation between DA and AA was large up to 220 mV. Using DPV technique, the calibration curve for DA determination was obtained in the range of 0.05-10 μM. The detection limit for DA was 20 nM. AA did not interfere with the determination of DA because of the very distinct attractive interaction between DA cations and the negatively Gr/p-ABA composite film. The proposed method exhibited good stability and reproducibility.