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.     

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.     

The Electrochemical Behavior of Neurotransmitters at a Poly (Pyrrole‐ β‐Cyclodextrin) Modified Glassy Carbon Electrode

Abstract

A glassy carbon electrode surface was modified with an electropolymerized film made of pyrrole and β‐cyclodextrin 1∶1, in a 0.1 M LiClO₄ solution using cyclic voltammetry. The resulting modified electrode (Ppy/β‐CD) exhibits interesting electrocatalytic activity toward the electrochemical oxidation of neurotransmitters such as dopamine (DA) and norepinephrine (NE). Well‐resolved and reversible cyclic voltammograms (CVs) were obtained for these organic compounds in a 0.1 M H₂SO₄ solution. The effect of the pH on the voltammetric response of DA and NE was also investigated inside the range of pH 2.8–8.4. The oxidation current of norepinephrine increase linearly with the concentration inside the range of 4×10^?7 M–2×10^?6 M. The oxidation current of dopamine also followed the same trend range of 2×10^?6 M–10^?5 M. The detection limit was 6×10^?6 M for (DA) and 8×10^?7 M for (NE). As an example, the relative standard deviation for 1×10^?5 M of DA was 2.056%. The diffusion coefficients D for the molecules studied were determined by means of the measurement of the effect of the scan rate on the CVs of the neurotransmitters. All the results showed that the electron transfer was predominantly diffusion controlled at the conducting polymer/solution interface.

Interference phenomenon due to ascorbic acid (AA) toward the neurotransmitters was also investigated. The novel modified electrodes presented capability to resolve perfectly the AA and neurotransmitters oxidation peaks. This performance could be achieved even at a concentration 20 times higher than the neurotransmitters.

Finally, the newly fabricated Ppy/β‐CD film exhibits interesting analytical performances compared with other systems in the literature, such as higher sensitivity, rapid response, good mechanical stability and reproducibility.     

Synthesis and characterization of NiFe2O4 nanoparticles using the hydrothermal method as magnetic catalysts for electrochemical detection of norepinephrine in the presence of folic acid

In this article, we present a simple and efficient method to synthesize a magnetic NiFe₂O₄ nanocatalyst under hydrothermal conditions. Fourier transform infrared spectroscopy (FT‐IR), X‐ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X‐ray spectroscopy (EDX) analyses confirmed the synthesis of NiFe₂O₄ nanoparticles. These nanoparticles showed satisfactory catalytic activity for determination of norepinephrine (NE) in the presence of folic acid (FA) using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods. Differential pulse voltammetry peak currents of NE increased linearly with their concentrations in the range of 1.0 × 10^?7–5.0 × 10^?4 M, and the detection limit for NE was 2.3 × 10^?8 M, respectively. The modified electrode displayed strong function for resolving the overlapping voltammetric responses of NE and FA into two well‐defined voltammetric peaks. In the mixture containing NE and FA, the two compounds can well separate from each other with a potential difference of 510 mV between NE and FA, which was large enough to determine NE and FA individually and simultaneously. Additionally, the prepared electrochemical sensor demonstrated a practical feasibility for real sample determination.     

Simultaneous Determination of Dopamine and Ascorbic Acid at an In‐Site Functionalized Self‐Assembled Monolayer on Gold Electrode

The in‐site functionalization of 4‐aminothiophenol (4‐ATP) self‐assembled monolayer on gold electrode at physiological pH yields a redox active monolayer of 4′‐mercapto‐N‐phenylquinone diimine (MNPD). The functionalized electrode exhibits excellent electrocatalytic responses towards dopamine (DA) and ascorbic acid (AA), reducing the overpotentials by about 0.22 V and 0.34 V, respectively, with greatly enhanced current responses. Due to its different catalytic activities toward DA and AA, the modified electrode resolves the overlapping voltammetric responses of DA and AA into two well‐defined voltammetric peaks by 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 concentration in the ranges of 5.0×10^?6?1.25×10^?4 M and 8.0×10^?6?1.3×10^?4 M with correlation coefficient of 0.999 and 0.998, respectively. The detective limits (3σ) for DA and AA were found to be 1.2×10^?6 M and 2.4×10^?6 M, respectively. The modified electrode shows good sensitivity, selectivity and stability, and has been applied to the determination of DA and AA simultaneously in samples with satisfactory results.     

The Influence of Gold Nanoparticles on Simultaneous Determination of Uric Acid and Ascorbic Acid

A three-dimensional L-cysteine (L-cys) monolayer assembled on gold nanoparticles (GNP) providing simultaneous detection of uric acid (UA) and ascorbic acid (AA) was studied in this work. The cyclic voltammetry demonstrated that, at a bare glassy carbon electrode (GCE) or planar gold electrode, the mixture of UA and AA showed one overlapped oxidation peak; whereas when the electrode was modified with GNP, the oxidation peaks for UA and AA were separated. While a GNP modified electrode was further modified with L-cys monolayer (L-cys/GNP/GCE), namely, three-dimensional L-cys monolayer, a better separation for UA and AA response was obtained. Interestingly, the L-cys monolayer-modified planar gold electrode presented a block effect on the oxidation of AA, which was facilitated by the three-dimensional L-cys monolayer attributed to its distinct structure. The pH of solution presented a noticeable effect on the separation of UA and AA at GNP modified electrodes with or without L-cys monolayer. Wide concentration ranges from 2 × 10^?6?1 × 10^?3 M to UA and 2 × 10^?6?8 × 10^?4 M to AA could be obtained at L-cys/GNP/GCE.     

A Novel Sensitive Biosensor for Ca2+ Ion Based on Gold Nanoparticles Modified Electrode by Pulsed Electrodeposition

The work demonstrates a simple method for sensitive detection of Ca²⁺ ion by electrochemical response of alizarin red S (ARS) and Ca-ARS at a gold nanoparticle modified glassy carbon electrode (GCE). In the 0.1 M KOH, a sensitive reduction peak was observed at ?0.795 V at the gold nanoparticles modified electrode. The peak currents were proportional to the concentrations of Ca²⁺ ion in the range of 2.0 × 10^?7 M–1.2 × 10^?4 M. For the different pulse voltammetry (DPV) methods, the detection limit was 2.57 × 10^?8 M. The reaction mechanism was primarily determined by cyclic voltammetry, and the experimental results showed that the electrode processes were quasireversible responses of ARS and irreversible responses of ARS-Ca. In addition, the method was simple, fast, precise, and was used in the determination of calcium in blood serum with satisfactory results.     

Electrochemical determination of norepinephrine on the membrane of silver nanoparticles doped poly-glycine eliminating the interference of ascorbic acid

The silver nanoparticles doped poly-glycine composite membrane was prepared by cyclic voltammetry on the surface of the glassy carbon electrode (GCE). The morphology and electrochemical properties were characterized by scanning electron microscopy and cyclic voltammetry, respectively, and in detail, the electrochemical behaviors of the norepinephrine (NE) on this membrane were studied. The results showed that the membrane had good catalytic properties for the oxidative–reductive reaction of NE. NE had a couple of sensitive oxidative-reductive current peaks. The reductive peak currents were linearly with its concentration in the range of 1.90?×?10^?7 to 7.00?×?10^?6 and 7.00?×?10^?6 to 1.00?×?10^?4?mol l^?1, and the linear regressive equations were i _pc (A)?=?3.73?×?10^?6?+?0.70C (mol l^?1), i _pc (A)?=?9.83?×?10^?5?+?0.12C (mol l^?1), respectively, with the relate coefficient (r) of 0.9926 and 0.9944. The detection limit was 1.2?×?10^?7?mol l^?1 (S/N?=?3), which could be used to determine the content of NE and at the same time, eliminate the interference of the ascorbic acid (AA). The proposed method had high sensitivity, good selectivity and stability.     

Electrochemical Behavior of a Gold Electrode Modified with SWNTs/DDAB Films and Its Electrocatalytic Activity Towards Ascorbic Acid

A film of single-wall carbon nanotubes (SWNTs) and didodecyldimethylammonium bromide (DDAB) is prepared by casting a solution of SWNTs and DDAB onto the surface of a gold electrode. The electrochemical behavior of the film is investigated by electrochemical impedance spectroscopy and cyclic voltammetry. In a 0.10 M phosphate buffer solution of pH 7.0, the film-modified electrode gives a pair of redox peaks in cyclic voltamograms, with the anodic and cathodic peak potentials of 0.095 and 0.042 V. The peak currents change linearly with the scan rate at 30–500 mV/s. The modified electrode has an excellent electrocatalytic activity towards the oxidation of ascorbic acid (AA). The catalysis currents are proportional to the AA concentration in the range of 5.0 × 10⁻⁴ to 3.2 × 10⁻² M. The linear-regression equation is i (μA) = 1.2079 + 1.3987 × 10³ c _AA (M), with a correlation coefficient of 0.9995. The detection limit is 2.2 × 10⁻⁴ M (signal-to-noise ratio of 3). The Michaelis-Menten constant (K _m) is 1.0 × 10⁻⁴ M by the Lineweaver-Burk equation. __________ From Elektrokhimiya, Vol. 41, No. 10, 2005, pp. 1193–1199. Original English Text Copyright ? 2005 by Cheng, Jin, Zhang. The text was submitted by the authors in English.     

Catalytic Oxidation of Dopamine at a Nickel Hexacyanoferrate Surface Modified Graphite Wax Composite Electrode Coated with Nafion

A chemically modified electrode was successfully fabricated by means of depositing a thin layer of nickel hexacyanoferrate (NiHCF) on an amine adsorbed graphite paraffin wax composite electrode using a new approach. The electrode was further coated with Nafion. The electrochemical characteristics of the modified electrode were studied using cyclic voltammetry and electrochemical impedance spectroscopy (EIS). The modified electrode catalyzed dopamine (DA) oxidation in the concentration range of 1.5×10^?6 to 1.2×10^?3 M without the interference from ascorbic acid (AA). A detection limit of 4.9×10^?7 M was obtained for DA in the presence of AA with a correlation coefficient of 0.9972 based on S/N=3. Flow injection analysis was used for the determination of dopamine with excellent reproducible results. The analytical utility of the sensor was evaluated for detection of DA in urine.     

Square Wave Voltammetry for Selective Detection of Dopamine Using Polyglycine Modified Carbon Ionic Liquid Electrode

The electrochemical polymerization of glycine on carbon ionic liquid electrode (CILE) was described. The presence of ionic liquid on the surface of CILE facilitated the electropolymerization of glycine. The polyglycine modified CILE provided a valid and simple approach to selectively detect dopamine in the presence of AA in physiological environment. The proposed sensor not only decreased the voltammetric responses of AA but also dramatically enhanced the oxidation peak current of DA compared to bare CILE. Using square wave voltammetry, the modified CILE showed good electrochemical behavior to DA, a linear range of 1.0×10^?7–3.0×10^?4 M in the presence of 1 mM ascorbic acid (AA) and a detection limit of 5.0×10^?9 M was estimated (S/N=3).     

Electrochemical Analysis of D‐Penicillamine Using a Carbon Paste Electrode Modified with Ferrocene Carboxylic Acid

The electrochemical behavior of D ‐penicillamine (D ‐PA) studied at the surface of ferrocene carboxylic acid modified carbon paste electrode (FCAMCPE) in aqueous media using cyclic voltammetry and double step potential chronoamperometry. It has been found that under optimum condition (pH 7.00), the oxidation of D ‐PA at surface of such an electrode is occurred about 420 mV less positive than that an unmodified carbon paste electrode (CPE). The catalytic oxidation peak current was linearly dependent on the D ‐PA concentration and a linear calibration curve was obtained in the ranges 7.5×10^?5 M – 1.0×10^?3 M and 6.5×10^?6 M?1.0×10^?4 M of D ‐PA with cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods respectively. The detection limits (3σ) were determined as 6.04×10^?5 M and 6.15×10^?6 M. This method was also used for the determination of D ‐PA in pharmaceutical preparation (capsules) by standard addition method.     

A Selective Voltammetric Method for Uric Acid Detection at a Glassy Carbon Electrode Modified with Electrodeposited Film Containing DNA and Pt‐Fe(III) Nanocomposites

A novel biosensor by electrochemical codeposited Pt‐Fe(III) nanocomposites and DNA film was constructed and applied to the detection of uric acid (UA) in the presence of high concentration of ascorbic acid (AA). Based on its strong catalytic activity toward the oxidation of UA and AA, the modified electrode resolved the overlapping voltammetric response of UA and AA into two well‐defined peaks with a large anodic peak difference (ΔE_pa) of about 380mV. The catalytic peak current obtained from differential pulse voltammetry (DPV) was linearly dependent on the UA concentration from 3.8×10^?6 to 1.6×10^?4 M (r=0.9967) with coexistence of 5.0×10^?4 M AA. The detection limit was 1.8×10^?6 M (S/N=3) and the presence of 20 times higher concentration of AA did not interfere with the determination. The modified electrode shows good sensitivity, selectivity and stability.     

Simultaneous Determination of Ascorbic Acid,Dopamine and Uric Acid at Pt Nanoparticles Decorated Multiwall Carbon Nanotubes Modified GCE

A modified electrode was fabricated by electrochemically deposition of Pt nanoparticles on the multiwall carbon nanotube covered glassy carbon electrode (Pt nanoparticles decorated MWCNT/GCE). A higher catalytic activity was obtained to electrocatalytic oxidation of ascorbic acid, dopamine, and uric acid due to the enhanced peak current and well‐defined peak separations compared with both, bare and MWCNT/GCE. The electrode surfaces were characterized by scanning electron microscopy (SEM), X‐ray diffraction (XRD) and electrochemical impedance spectroscopy (EIS). Individual and simultaneous determination of AA, DA, and UA were studied by differential pulse voltammetry. The detection limits were individually calculated for ascorbic acid, dopamine, and uric acid as being 1.9×10^?5 M, 2.78×10^?8 M, and 3.2×10^?8 M, respectively. In simultaneous determination, LODs were calculated for AA, DA, and UA, as of 2×10^?5 M, 4.83×10^?8 M, and 3.5×10^?7 M, respectively.     

Modified glassy carbon electrode by electropolymerization of tetrakis-(2-aminopheny)porphyrin for the determination of norepinephrine in the presence of ascorbic acid

A glassy carbon electrode (GCE) was modified with electropolymerization of meso-tetrakis(2-aminophenyl)porphyrin (TAPP) in acetonitrile by cyclic voltammetry (CV). The voltammetric behavior of norepinephrine (NE) in the presence of excess ascorbic acid (AA) was investigated at the modified electrode by cyclic and square wave voltammetry (SWV) in phosphate buffer solution. The modified electrode gave higher selectivity and highly effective electroactivity to NE oxidation in voltammetric measurements of NE in the presence of AA and epinephrine. In pH 7.4 phosphate buffer solution, the peak current increased linearly with the concentration of NE in two concentration ranges of 1.0×10⁻⁶ to 5.0×10⁻⁵ mol dm⁻³.     

Development of Voltammetric Sensor for Determination of Tryptophan Using MWCNTs‐modified Sol‐gel Electrode

In the present work, an electrochemical sensor was developed for simple and sensitive determination of tryptophan (Trp) using multi‐walled carbon nanotubes modified sol‐gel electrode (MWCNTs/SGE). The electrocatalytic oxidation of tryptophan was investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). It was found that the oxidation peak current of Trp at the MWCNTs/SGE was greatly improved compared with that of the bare SGE. Furthermore, at the MWCNTs/SGE, the anodic peak potential of Trp is shifted about 220 mV to more negative value indicated that modified electrode has better electrocatalytic activity for electro‐oxidation of Trp. The anodic peak currents increased linearly with the concentration of tryptophan in the range of 0.2 × 10^?6 to 15 × 10^?6 M with a detection limit of 0.139 × 10^?6 M (at an S/N = 3).     

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.     

Preparation of Polypyrrole/Nuclear Fast Red Films on Gold Electrode and Its Application on the Electrocatalytic Determination of Methyl‐dopa and Ascorbic Acid

A novel voltammetric method using the Ppyox/NFR/Au (poly pyrrole – nuclear fast red – gold) modified electrode was developed for simultaneous measurement of various combinations of ascorbic acid (AA) and methyldopa (MDA). Polypyrrole film was prepared by incorporation of nuclear fast red (NFR) as doping anion, during the electropolymerization of pyrrole onto a gold (Au) electrode in aqueous solution using cyclic voltammetric (CV) method, and then it was overoxidized at constant potential. Differential pulse voltammetry was utilized for the measurement of both analytes using modified electrode. Well‐separated voltammetric peaks were observed for ascorbic acid (AA) and methyldopa at the Ppyox/NFR/Au modified electrodes with peak separation of 0.210 V. It has been found that under optimum condition (pH 3.0), the oxidation of AA and MDA at the surface of the electrode occurs at a potential about 260 and 50 mV less positive than unmodified Au electrode respectively. The current catalytic oxidation peaks showed a linear dependent on the concentration of AA and MDA in the range of 9.0×10^?6 to 1.0×10^?3 and 1.0×10^?7 to 2.0×10^?5 mol L^?1 respectively. The detection limit of 5.8×10^?6 and 5.0×10^?8 mol L^?1 (S/N=3) were obtained for AA and MDA respectively. The modified electrode was used for determination of AA and MDA in some real samples such as human serum and tablet.     

Voltammetric Determination of Adrenaline Using a Poly(1‐Methylpyrrole) Modified Glassy Carbon Electrode

A voltammetric method using a poly(1‐methylpyrrole) modified glassy carbon electrode was developed for the quantification of adrenaline. The modified electrode exhibited stable and sensitive current responses towards adrenaline. Compared with a bare GCE, the modified electrode exhibits a remarkable shift of the oxidation potentials of adrenaline in the cathodic direction and a drastic enhancement of the anodic current response. The separation between anodic and cathodic peak potentials (ΔEp) for adrenaline is 30 mV in 0.1 M phosphate buffer solution (PBS) at pH 4.0 at modified glassy carbon electrodes. The linear current response was obtained in the range of 7.5 × 10^?7 to 2.0 × 10^?4 M with a detection limit of 1.68 × 10^?7 M for adrenaline by square wave voltammetry. The poly(1‐methypyrrole)/GCE was also effective to simultaneously determine adrenaline, ascorbic acid and uric acid in a mixture and resolved the overlapping anodic peaks of these three species into three well‐defined voltammetric peaks in cyclic voltammetry. The modified electrode has been successfully applied for the determination of adrenaline in pharmaceuticals. The proposed method showed excellent stability and reproducibility.     

Fabrication of Fe3O4 Nanoparticles Modified Electrode and Its Application for Voltammetric Sensing of Dopamine

Magnetic nanoparticles of Fe₃O₄ approximately 5nm in size were synthesized and characterized by XRD and TEM. A novel gold electrode modified with Fe₃O₄ nanoparticles was then constructed and was characterized by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The modified electrode exhibited strong promoting effect and high stability toward the electrochemical oxidation of dopamine (DA), which gave reversible redox peaks with a formal potential of 0.192 V (vs. Ag/AgCl) electrode in pH 7.0 phosphate buffer solution (PB). The anodic peak currents (measured by constant potential amperometry) increased linearly with the concentration of dopamine in the range of 1.5×10^?7 to 4.0×10^?4 M. The detection limit (S/N=3) obtained was 3.0×10^?8 M. The relative standard deviation (RSD) of 8 successive scans was 3.41% for 1.5×10^?6 M DA. The interference of ascorbic acid (AA) could be eliminated efficiently. The proposed method showed excellent sensitivity and recovery.