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.     

Simultaneous electrochemical determination of norepinephrine,ascorbic acid and uric acid using a graphene modified glassy carbon electrode

This paper describes the simultaneous determination of ascorbic acid (AA), norepinephrine (NE) and uric acid (UA) using a graphene modified glassy carbon electrode (GME) in pH 4.0 phosphate buffer solution. The electrochemical behaviors of AA, NE and UA at a bare glassy carbon electrode (GCE) and the GME were studied by cyclic voltammetry. Bare GCE failed to resolve the voltammetric signals of AA, NE and UA in a mixture, whereas the GME not only resolved their voltammetric signals, but also exhibited excellent electrocatalytic activity towards their electrochemical oxidation. The oxidation peak currents of AA, NE and UA were linearly proportional to their concentrations over the range of 1.0.0–1000.0, 0.6–45.0 and 1.0–100.0 μM, respectively, and their detection limits were 1.2, 0.10 and 0.60 μM, respectively, The modified electrode is of excellent sensitivity and selectivity, and has been satisfactorily used for the simultaneous determination of AA, NE and UA in their ternary mixture.     

Simultaneous electrochemical determination of uric acid and ascorbic acid on a glassy carbon electrode modified with cobalt(II) tetrakisphenylporphyrin.

A cobalt(II) tetrakisphenylporphyrin (Co(II)TPP) film modified glassy carbon electrode (Co(II)TPP-GCE) was prepared by just coating Co(II)TPP solution on the surface of the electrode. It can be used for the simultaneous determination of ascorbic acid and uric acid. The anodic peaks of AA and UA can be separated well. Owing to the strongly hydrophobic property of porphyrin, the modified electrode has good stability and long life. The linear range for UA and AA were 2.0 x 10(-6)-1.0 x 10(-4) M and 9.0 x 10(-6)-2.0 x 10(-3) M with detection limits of 5.0 x 10(-7) and 5.0 x 10(-6) M, respectively. Furthermore, metalloporphyrins of other kinds were also used to construct modified electrodes. Their performances were inferior compared with that of the Co(II)TPP modified electrode.     

Simultaneous determination of tryptophan, uric acid and ascorbic acid at iron(III) doped zeolite modified carbon paste electrode

A new chemically modified electrode is constructed based on iron(III) doped zeolite modified carbon paste electrode (Fe(3+)Y/ZCME). The electrode was evaluated as a sensor for sub-micromolar determination of tryptophan (Trp), uric acid (UA) and ascorbic acid (AA) in aqueous solutions. The measurements were carried out by application of the differential pulse voltammetry (DPV) method in phosphate buffer solution with pH 3.5. Iron(III) loaded in zeolite can increase anodic peak currents by adsorption of Trp, UA and AA on electrode surface The analytical performance was evaluated with respect to the carbon paste composition, pH of solution, accumulation time and accumulation potential. The prepared electrode shows voltammetric responses with high sensitivity and selectivity for Trp, UA and AA in optimal conditions, which makes it very suitable for simultaneous determination of these compounds. The linear calibration range for AA in the presence of 50muM UA and 50muM Trp was 0.6muM to 100muM, with a correlation coefficient of 0.9992, and a detection limit of 0.21muM (S/N=3). A linear relationship was found for UA in the range of 0.3-700muM containing 10muM AA and 50muM Trp, with a correlation coefficient of 0.9990 and a detection limit of 0.08muM. The linear calibration range for Trp in the presence of 10muM AA and 50muM UA was 0.2-150muM, with a correlation coefficient of 0.9996, and a detection limit of 0.06muM. The proposed method was successfully applied for determination Trp, UA and AA in biological systems and pharmaceutical samples.     

槲皮素在聚谷氨酸修饰玻碳电极上的伏安行为及检测

制备了聚谷氨酸修饰玻碳电极,通过循环伏安法和差分脉冲伏安法研究了槲皮素在该修饰电极上的电化学行为。在pH 5.00的B-R缓冲液中,槲皮素在修饰电极上于0.28 V(vs Ag/AgCl)电位处产生一个灵敏的DPV阳极氧化峰,氧化峰电流与槲皮素的浓度在1.0×10-8～5×10-5 mol/L的范围内呈良好的线性关系,最低检测限为4.0×10-9 mol/L。实验表明,聚谷氨酸修饰电极可提高槲皮素的检测灵敏度,该电极用于芦丁水解产物中槲皮素的检测,回收率为103.4%～104.5%。     

Simultaneous determination of dopamine and ascorbic acid on poly (3,4-ethylenedioxythiophene) modified glassy carbon electrode

Detection of dopamine (DA) in the presence of excess of ascorbic acid (AA) has been demonstrated using a conducting polymer matrix, poly (3,4-ethylenedioxythiophene) (PEDOT) film in neutral buffer (PBS 7.4) solution. The PEDOT film was deposited on a glassy carbon electrode by electropolymerization of EDOT from acetonitrile solution. Atomic force microscopy studies revealed that the electrodeposited film was found to be approximately 100 nm thick with a roughness factor of 2.6 nm. Voltammetric studies have shown catalytic oxidation of DA and AA on PEDOT modified electrode and can afford a peak potential separation of ∼0.2 V. It is speculated that the cationic PEDOT film interacts with the negatively charged ascorbate anion through favorable electrostatic interaction, which results in pre-concentration at a less anodic value. The positively charged DA tends to interact with the hydrophobic regions of PEDOT film through hydrophobic–hydrophobic interaction thus resulting in favorable adsorption on the polymer matrix. Further enhancement in sensitivity to micro molar level oxidation current for DA/AA oxidation was achieved by square wave voltammetry (SWV) which can detect DA at its low concentration of 1 μM in the presence of 1000 times higher concentration of AA (1 mM). Thus the PEDOT modified electrode exhibited a stable and sensitive response to DA in the presence of AA interference.     

Simultaneous determination of ascorbic acid,epinephrine, and uric acid by differential pulse voltammetry using poly(p-xylenolsulfonephthalein) modified glassy carbon electrode

A novel poly(p-xylenolsulfonephthalein) modified glassy carbon electrode was prepared for the simultaneous determination of ascorbic acid (AA), epinephrine (EP) and uric acid (UA). Cyclic voltammetric, chronoamperometric, and differential pulse voltammetric methods were used to investigate the modified electrode for the electrocatalytic oxidation of EP, AA, and UA in aqueous solutions. The separation of the oxidation peak potentials for AA–EP and EP–UA was about 200 and 130 mV, respectively. The calibration curves obtained for AA, EP, and UA were in the ranges of 10–1343, 2–390, and 0.1–560 μmol L⁻¹, respectively. The detection limits (S/N = 3) were 4, 0.1, and 0.08 μmol L⁻¹ for AA, EP and UA, respectively. The diffusion coefficient and the catalytic rate constant for the oxidation of EP at the modified electrode were calculated as 1.40(±0.10) × 10⁻⁴ cm² s⁻¹ and 1.06 × 10³ mol⁻¹ L s⁻¹, respectively. The present method was applied to the determination of EP in pharmaceutical and urine samples, AA in commercially available vitamin C tablet, and EP plus UA in urine samples.     

Simultaneous determination of uric acid and ascorbic acid at the film of chitosan incorporating cetylpyridine bromide modified glassy carbon electrode

A glassy carbon electrode (GCE) modified with the film composed of chitosan incorporating cetylpyridine bromide is constructed and used to determine uric acid (UA) and ascorbic acid (AA) by differential pulse voltammetry (DPV). This modified electrode shows efficient electrocatalytic activity and fairly selective separation for oxidation of AA and UA in mixture solution. UA is catalyzed by this modified electrode in phosphate buffer solution (pH 4.0) with a decrease of 80 mV, while AA is catalyzed with a decrease of 200 mV in overpotential compared to GCE, and the peak separation of oxidation between AA and UA is 260 mV, which is large enough to allow the determination of one in presence of the other. Under the optimum conditions, the anodic peak currents (I _pa) of DPV are proportional to the concentration of UA in the range of 2.0 × 10⁻⁶ to 6.0 × 10⁻⁴ M, with the detection limit of 5.0 × 10⁻⁷ M at a signal-to-noise ratio of 3 (S/N = 3) and to that of AA in the range of 4.0 × 10⁻⁶ to 1.0 × 10⁻³ M, with the detection limit of 8.0 × 10⁻⁷ M (S/N = 3).     

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.     

Poly(isonicotinic acid) modified glassy carbon electrode for electrochemical detection of norepinephrine

A glassy carbon electrode (GCE) was modified with electropolymerized films of isonicotinic acid in pH 5.6 phosphate buffer solution (PBS) by cyclic voltammetry (CV). The modified electrode showed an excellent electrocatalytical effect on the oxidation of norepinephrine (NE). In PBS of pH 7.4, the oxidation current increased linearly with two concentration intervals of NE, one is 4.0×10⁻⁷ to 1.0×10⁻⁵ M, the other is 1.0×10⁻⁵ to 2.0×10⁻⁴ M. The detection limit (S/N=3) obtained by DPV was 6.0×10⁻⁹ M. Then the modified electrode was used to determine NE in an excess of ascorbic acid (AA) by difference pulse voltammetry. The peak potentials recorded in a PBS of pH 7.4 were −68 and +111 mV versus SCE for AA and NE, respectively. The high selectivity and sensitivity for NE was found to be due to the very distinct attracting interaction between NE cations and the negtively charged poly(isonicotinic acid) film in pH 7.4 PBS. The proposed method exhibited good recovery and reproducibility.     

Simultaneous voltammetric measurement of ascorbic acid and dopamine on poly(caffeic acid)-modified glassy carbon electrode

A poly(caffeic acid) thin film was deposited on the surface of a glassy carbon electrode by potentiostatic technique in an aqueous solution containing caffeic acid. The poly(caffeic acid)-modified electrode was used for the determination of ascorbic acid (AA), dopamine (DA), and their mixture by cyclic voltammetry. This modified electrode exhibited a potent and persistent electron-mediating behavior followed by well-separated oxidation peaks toward AA and DA at a scan rate of 10 mV s⁻¹ with a potential difference of 135 mV, which was large enough to determine AA and DA individually and simultaneously. The catalytic peak current obtained was linearly dependent on the AA and DA concentrations in the range of 2.0 × 10⁻⁵−1.2 × 10⁻³ and 1.0 × 10⁻⁶−4.0 × 10⁻⁵ mol L⁻¹ in 0.15 mol L⁻¹ phosphate buffer (pH 6.64). The detection limits for AA and DA were 9.0 × 10⁻⁶ and 4.0 × 10⁻⁷ mol L⁻¹, respectively. The modified electrode shows good sensitivity, selectivity, and stability and has been applied to the determination of DA and AA in real samples with satisfactory results.     

抗坏血酸在聚阿魏酸修饰玻碳电极上的电化学行为研究

研究了抗坏血酸(AA)在聚阿魏酸修饰电极上的电化学性质。在AA存在的条件下,电极过程由扩散控制,测得扩散系数为8.18×10-8cm2/s。AA浓度在0.01~5.0 mmol/L范围内与峰电流呈现良好的线性关系。通过计时安培法测得催化速率常数为8.6×103mol-1.L.s-1。     

用聚(L-蛋氨酸)/纳米金修饰玻碳电极同时灵敏检测多巴胺和尿酸简

A novel electrochemical sensor was fabricated by electrodeposition of gold nanoparticles on a poly(L-methionine) (PMT)-modified glassy carbon electrode (GCE) to form a nano-Au/PMT composite-modified GCE (nano-Au/PMT/GCE). Scanning electron microscopy and electrochemical techniques were used to characterize the composite electrode. The modified electrode exhibited considerable electrocatalytic activity towards the oxidation of dopamine (DA) and uric acid (UA) in phosphate buffer solution (pH = 7.00). Differential pulse voltammetry revealed that the electrocatalytic oxidation currents of DA and UA were linearly related to concentration over the range of 5.0×10^-8 to 10^-6 mol/L for DA and 7.0×10^-8 to 10^-6 mol/L for UA. The detection limits were 3.7×10^-8 mol/L for DA and 4.5×10^-8 mol/L for UA at a signal-to-noise ratio of 3. According to our experimental results, nano-Au/PMT/GCE can be used as a sensitive and selective sensor for simultaneous determination of DA and UA.     

Simultaneous determination of dopamine and ascorbic acid at a poly(toluidine blue) modified electrode.

A novel polymer modified electrode is discussed in this paper. This resulting electrode can catalyze remarkably toward the electrochemical oxidations of dopamine (DA) and ascorbic acid (AA). Moreover, it can clearly discriminate the electrochemical oxidations of DA from that of AA based on their semi-derivative voltammograms. Hence, a simultaneous determination of DA and AA based on semi-derivative voltammetry at a poly(toluidine blue) modified electrode is suggested. The detection linear range for DA is 0.4 micromol L(-1)-1.5 mmol L(-1), and AA 0.2 micromol L(-1)-2.4 mmol L(-1), respectively. The resulting modified electrode was tentatively used to determine DA and AA in brain tissue.     

A glassy carbon electrode modified with MoS<Subscript>2</Subscript> nanosheets and poly(3,4-ethylenedioxythiophene) for simultaneous electrochemical detection of ascorbic acid,dopamine and uric acid

We describe a chemical exfoliation method for the preparation of MoS₂ nanosheets. The nanosheets were incorporated into poly(3,4-ethylenedioxythiophene) (PEDOT) by electrodeposition on a glassy carbon electrode (GCE) to form a nanocomposite. The modified GCE is shown to enable simultaneous determination of ascorbic acid (AA), dopamine (DA) and uric acid (UA). Due to the synergistic effect of MoS₂ and PEDOT, this electrode displays better properties in terms of electrocatalytic oxidation of AA, DA and UA than pure PEDOT, which is illustrated by cyclic voltammetry and differential pulse voltammetry (DPV). Under optimum conditions and at pH 7.4, the respective sensitivities and best working potentials are as follows: AA: 1.20 A?mM^?1?m^?2, 30 mV; DA: 36.40 A?mM^?1?m^?2, 210 mV; UA: 105.17 A?mM^?1?m^?2, 350 mV. The calculated detection limits for AA, DA and UA are 5.83 μM, 0.52 μM and 0.95 μM, respectively. The modified electrode was applied to the detection of the three species in human urine samples and gave satisfactory results.

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Graphical abstract MoS₂ nanosheets were prepared by a facile chemical exfoliation method. MoS₂ and poly(3,4-ethylenedioxythiophene) nanocomposite modified glassy carbon electrodes were fabricated, which are shown to enable simultaneous determination of ascorbic acid, dopamine and uric acid with high sensitivity and selectivity.

     

Simultaneous electrochemical sensing of ascorbic acid,dopamine and uric acid at anodized nanocrystalline graphite-like pyrolytic carbon film electrode

Nanocrystalline graphite-like pyrolytic carbon film (PCF) electrode fabricated by a non-catalytic chemical vapor deposition (CVD) process was used for the simultaneous electrochemical sensing of ascorbic acid (AA), dopamine (DA), and uric acid (UA). The electrode was studied with respect to changes in electrocatalytic activity caused by a simple and fast electrochemical pretreatment. The anodized electrode exhibited excellent performance compared to many chemically modified electrodes in terms of detection limit, linear dynamic range, and sensitivity. Differential pulse voltammetry (DPV) was used for the simultaneous determination of ternary mixtures of DA, AA, and UA. Under optimum conditions, the detection limits were 2.9 μM for AA, 0.04 μM for DA, and 0.03 μM for UA with sensitivities of 0.078, 5.345, and 6.192 A M⁻¹, respectively. The peak separation was 219 mV between AA and DA and 150 mV between DA and UA. No electrode fouling was observed and good reproducibility was obtained in all the experiments. The sensor was successfully applied for the assay of DA in an injectable drug and UA in human urine by using standard addition method.     

Simultaneous determination of ascorbic acid,dopamine, uric acid and tryptophan on gold nanoparticles/overoxidized-polyimidazole composite modified glassy carbon electrode

A novel electrode was developed through electrodepositing gold nanoparticles (GNPs) on overoxidized-polyimidazole (PImox) film modified glassy carbon electrode (GCE). The combination of GNPs and the PImox film endowed the GNPs/PImox/GCE with good biological compatibility, high selectivity and sensitivity and excellent electrochemical catalytic activities towards ascorbic acid (AA), dopamine (DA), uric acid (UA) and tryptophan (Trp). In the fourfold co-existence system, the peak separations between AA–DA, DA–UA and UA–Trp were large up to 186, 165 and 285 mV, respectively. The calibration curves for AA, DA and UA were obtained in the range of 210.0–1010.0 μM, 5.0–268.0 μM and 6.0–486.0 μM with detection limits (S/N = 3) of 2.0 μM, 0.08 μM and 0.5 μM, respectively. Two linear calibrations for Trp were obtained over ranges of 3.0–34.0 μM and 84.0–464.0 μM with detection limit (S/N = 3) of 0.7 μM. In addition, the modified electrode was applied to detect AA, DA, UA and Trp in samples using standard addition method with satisfactory results.     

Simultaneous determination of ascorbic acid,dopamine and serotonin at poly(phenosafranine) modified electrode

The oxidation of phenosafranine at glassy carbon electrode gives rise to stable redox active electropolymerized film containing a polyazine moiety (poly(phenosafranine)). The redox response of the poly(phenosafranine) film was observed at the modified electrode at different pH and the pH dependence of the peak potential is 60 mV/pH, which is very close to the expected Nernstian behavior. The apparent diffusion coefficient (D_app) of poly(phenosafranine) film was measured as 2.51 × 10⁻⁹ cm²/s. This film exhibits potent and persistent electron-mediating behavior followed by well-separated oxidation peaks towards ascorbic acid (AA), dopamine (DA) and serotonin with activation overpotential, which is 200 mV lower than that of the bare electrode for AA oxidation. Using differential pulse voltammetry (DPV) studies, the limit of detection of DA in the presence of AA is estimated to be in the submicromolar regime. This method has been used for determining DA and AA concentrations in real samples with satisfactory results.     

Simultaneous determination of dopamine,ascorbic acid and uric acid with electrospun carbon nanofibers modified electrode

A novel carbon-nanofiber-modified carbon-paste electrode (CNF-CPE) was employed for the simultaneous determination of dopamine (DA), ascorbic acid (AA) and uric acid (UA) with good selectivity and high sensitivity. The CNFs were prepared by combination of electrospinning technique with thermal treatment method and were used without any pretreatment. In application to determination of DA, AA and UA in the ternary mixture, the pristine CNF-CPE exhibited well-separated differential pulse voltammetric peaks with high catalytic current. Low detection limits of 0.04 μM, 2 μM and 0.2 μM for DA, AA and UA were obtained, with the linear calibration curves over the concentration range 0.04–5.6 μM, 2–64 μM and 0.8–16.8 μM, respectively.