A quercetin-modified biosensor for amperometric determination of uric acid in the presence of ascorbic acid

The present work reports a quercetin-modified wax-impregnated graphite electrode (Qu/WGE) prepared through an electrochemical oxidation procedure in quercetin-containing phosphate buffer solution (PBS), for the purpose of detecting uric acid (UA) in the presence of ascorbic acid (AA). During modification quercetin was oxidized to the corresponding quinonic structure, and in the blank buffer solution the electrodeposited film exhibits a voltammetric response anticipated for the surface-immobilized quercetin. Retarding effect of the film towards the reaction of anionic species was found; therefore the pH of sample solutions was selected to ensure the analyte in molecular form. At suitable pHs the Qu/WGE shows excellent electrocatalytic effect towards the oxidation of both AA and UA, and separates the voltammetric signal of UA from AA by about 280 mV, allowing simultaneous detection of these two species. A linear relation between the peak current and concentration was obtained for UA in the range of 1-50 μM in the presence of 0.5 mM AA, with a detection limit 1.0 μM (S/N = 3). This sensor was stable, reproducible and outstanding for long-term use.     

Electrochemical determination of vitamin C in the presence of uric acid by a novel TiO2 nanoparticles modified carbon paste electrode

<正>The electrochemical behavior of vitamin C(ascorbic acid or AA) is investigated on the surface of a carbon-paste electrode modified with TiO_2 nanoparticles and 2,2'-(1,2 butanediylbis(nitriloethylidyne))-bis-hydroquinone(BBNBH).The prepared modified electrode showed an efficient catalytic role in the electrochemical oxidation of AA,leading to remarkable decrease in oxidation overpotential and enhancement of the kinetics of the electrode reaction.This modified electrode exhibits well-separated oxidation peaks for AA and uric acid(UA).The modified electrode is successfully applied for the accurate determination of AA in pharmaceutical preparations.     

Electrochemical determination of uric acid using a mesoporous SiO2-modified electrode

A mesoporous SiO₂-modified carbon paste electrode for the determination of uric acid is described. Owing to the regular and specific mesoporous channels, numerous active sites and a large surface area, the mesoporous SiO₂-modified electrode greatly increases the oxidation peak current of uric acid. Based on this, a highly sensitive, rapid and convenient electrochemical method was developed for the determination of uric acid after optimizing the experimental parameters (supporting electrolyte, content of mesoporous SiO₂, accumulation potential and time). The linear range is from 2.5 × 10⁻⁷ to 2.0 × 10⁻⁵ mol L⁻¹, and the limit of detection is estimated to be 8.0 × 10⁻⁸ mol L⁻¹. The relative standard deviation for 10 mesoporous SiO₂-modified electrodes is 5.8%. The method was used to determine uric acid in human serum samples. Correspondence: Kangbing Wu, Department of Chemistry, Huazhong University of Science and Technology, Wuhan 430074, P.R. China     

Selective determination of uric acid in the presence of ascorbic acid using a penicillamine self-assembled gold electrode

The electrochemical behaviors of uric acid (UA) at the penicillamine (Pen) self-assembled monolayers modified gold electrode (Pen/Au) have been studied. The Pen/Au electrode is demonstrated to promote the electrochemical response of UA by cyclic voltammetry (CV). The diffusion coefficient D of UA is 6.97 × 10⁻⁶ cm² s⁻¹. In differential pulse voltammetric (DPV) measurements, the Pen/Au electrode can separate the UA and ascorbic acid (AA) oxidation potentials by about 120 mV and can be used for the selective determination of UA in the presence of AA. The detection limit was 1 × 10⁻⁶ mol L⁻¹. The modified electrode shows excellent sensitivity, good selectivity and antifouling properties.     

Functionalized-graphene modified graphite electrode for the selective determination of dopamine in presence of uric acid and ascorbic acid

Graphene is chemically synthesized by solvothermal reduction of colloidal dispersions of graphite oxide. Graphite electrode is modified with functionalized-graphene for electrochemical applications. Electrochemical characterization of functionalized-graphene modified graphite electrode (FGGE) is carried out by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The behavior of FGGE towards ascorbic acid (AA), dopamine (DA) and uric acid (UA) has been investigated by CV, differential pulse voltammetry (DPV) and chronoamperommetry (CA). The FGGE showed excellent catalytic activity towards electrochemical oxidation of AA, DA and UA compared to that of the bare graphite electrode. The electrochemical oxidation signals of AA, DA and UA are well separated into three distinct peaks with peak potential separation of 193mv, 172mv and 264mV between AA-DA, DA-UA and AA-UA respectively in CV studies and the corresponding peak potential separations in DPV mode are 204mv, 141mv and 345mv. The FGGE is successfully used for the simultaneous detection of AA, DA and UA in their ternary mixture and DA in serum and pharmaceutical samples. The excellent electrocatalytic behavior of FGGE may lead to new applications in electrochemical analysis.     

Selective determination of L-dopa in the presence of ascorbic acid and uric acid using a 3D graphene foam

Three-dimensional interconnected network graphene foam (GF) was synthesized by chemical vapor deposition. The GF was transferred onto indium tin oxide glass, acting as an electrode for the selective determination of L-dopa in the presence of ascorbic and uric acid. Using differential pulse voltammetry (DPV) method, the oxidation peak current is well linear with L-dopa concentration in the range of 0.05–1 μM with a sensitivity of 2.64 μA μM^?1 and in the range of 1–40 μM with a sensitivity of 1.82 μA μM^?1. The detection limit of this electrode for L-dopa is about 20 nM. The proposed electrode can also effectively avoid the interference of ascorbic acid and uric acid, making the proposed sensor suitable for the accurate determination of L-dopa in human urine fluids. This electrode will have a wide range of potential application prospect in electrochemical detection.     

Electrochemical determination of tyrosine in the presence of uric acid at a carbon paste electrode modified with multi-walled carbon nanotubes enhanced by sodium dodecyl sulfate

Tyrosine (Tyr) was quantitated with high sensitivity and selectivity in the presence of uric acid (UA) using a carbon paste electrode modified with multi-walled carbon nanotubes. Tyr and UA were catalytically oxidized with diffusion-controlled characteristics. They were determined simultaneously by differential pulse voltammetry with a potential difference of 350 mV. The electrocatalytic currents increase linearly with Tyr and UA concentrations 4×10^?7?1×10^?4 M and 3×10^?7?2×10^?4 M. Their detection limits were 1×10^?7 and 5.1×10^?8 M respectively. In the presence of sodium dodecyl sulfate the Tyr detection limit improved from 1×10^?7 to 6.9×10^?8 M. The electrode was successfully used to quantitate Tyr and UA in serum.      

Electrochemical determination of dopamine in the presence of ascorbic acid and uric acid using the synergistic effect of gold nanoflowers and L-cysteamine monolayer at the surface of a gold electrode

This paper describes a facile and effective method to synthesize gold nanoflowers (AuNFs) by a controllable electrodeposition method induced by a L-cysteamine (L-Cys) monolayer self-assembled on the surface of a gold electrode. The AuNFs/L-Cys/Au electrodes were characterized by field emission scanning electron microscopy (FE-SEM), cyclic voltammetry, and AC impedance spectroscopy methods. This obtained AuNFs/L-Cys/Au electrode exhibits excellent electrocatalytic activity towards the oxidation of dopamine (DA) due to the synergistic effect of AuNFs and a L-Cys monolayer. Differential pulse voltammetry (DPV) experiment results show that the oxidation peak of DA is separated from the oxidation peaks of ascorbic acid (AA) and uric acid (UA), which can be used to detect DA in the presence of AA and UA, and the results are satisfactory.     

Simultaneous kinetic determination of uric acid ascorbic acid mixtures

A kinetic stopped-flow method is described for the simultaneous determination of uric acid and ascorbic acid with tris (2,2'-bipyridine)iron(III). For the least favourable ratios of uric to ascorbic acid, in a total concentration of 10^-5 M, the error in the determination of uric acid is estimated at ±10%.     

Electrochemical oxidation of sulfodifluoroacetic acid in the presence of halogens

The electrochemical oxidation of sulfodifluoroacetic acid (HOSO₂CF₂CO₂H) in the presence of Cl₂ or Br₂ gives halodifluoromethanesulfonic acid. The anodic oxidation of sulfodifluoromethanecarboxylate ion to form the sulfodifluoromethyl radical as an intermediate is proposed as the rate-determining step. Institute of Organic Chemistry, National Academy of Sciences of Ukraine, 5 Murmanskaya ul., Kiev 253094, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 35, No. 4, pp. 246–248, July–August, 1999.     

抗坏血酸和尿酸在CPB现场修饰碳糊电极上的电化学行为及其选择性测定应用

研究了抗坏血酸(AA)和尿酸(UA)在裸碳糊电极(CPE)和溴化十六烷基吡啶(CPB)现场修饰碳糊电极(CPB/CPE)上的电化学行为.研究结果表明,在PBS水溶液中,AA和UA在CPB/CPE上氧化峰电流增加,峰电位负移,CPB/CPE对AA,UA电化学氧化反应产生了催化作用.微分脉冲法研究表明,在AA和UA共存体系中,AA和UA的氧化峰电位相差约220 mV,以此建立了AA和UA的电化学选择性测定方法.AA和UA的微分脉冲伏安氧化峰电流和其相应浓度分别在7.0×10-6～6.0×10-3 mol/L和5.0×10-7～6.0×10-4 mol/L的范围内呈良好的线性关系.在200倍AA共存时UA的检出限为5.0×10-6 mol/L,CPB修饰的碳糊电极直接应用于实际尿样中UA的测定.     

Electrochemical oxidation of N-methylated derivatives of uric acid

The electrochemical oxidation of a number of N-methylated uric acids has been studied by linear and cyclic sweep voltammetry, coulometry and thin-layer spectroelectrochemistry. The observed results support the view that the electrooxidation is a 2e reaction to give a very unstable diimine primary product. This is rapidly hydrated to give an imine-alcohol which is further hydrated to give a uric acid-4,5-diol derivative which subsequently fragments to the various products.     

Spectrofluorimetric method for the determination of uric acid in human serum

A new spectrofluorimetric method is described for the determination of uric acid (UA), that can remarkably reduce the fluorescence intensity of the enoxacin (ENX)-terbium ion (Tb³⁺) complex at 545 nm. The reduced fluorescence intensity of Tb³⁺ ion at pH 5.7 is proportional to the concentration of UA. Optimum conditions for the determination of UA have been investigated. The linear range and detection limit for the determination of UA are 6.0 × 10^?7–3.0 × 10^?5 M and 1 × 10^?7 M, respectively. The relative standard deviation (RSD) was 0.4% for 6 × 10^?6 M UA (n = 11). The method is simple, practical and relatively free of interferences. It has been successfully applied to assess UA in serum at the level of 3 × 10^?4 M with an RSD of 5–7% (n = 3). The results were evaluated by comparison with a common clinical spectrophotometric method using phosphotungstic acid as developer.     

Electroanalysis and simultaneous determination of 6-thioguanine in the presence of uric acid and folic acid using a modified carbon nanotube paste electrode

The present work describes the preparation and characterization of a carbon nanotube paste electrode modified with 2,7-bis(ferrocenyl ethyl)fluoren-9-one (2,7-BF). This electrode showed an efficient catalytic activity for the electro-oxidation of 6-thioguanine (6-TG), which leads to lowering 6-TG overpotential by more than 610 mV. Also, the values of catalytic rate constant (k = 2.7 × 10(3) mol(-1) L s(-1)), and diffusion coefficient (D = 2.7 × 10(-5) cm(2) s) were calculated. In 0.1 M phosphate buffer solution of pH 7.0, the oxidation current increased linearly with two concentration intervals of 6-TG, one is 0.06 to 10.0 μmol L(-1) and the other is 10.0 to 160.0 μmol L(-1). The detection limit (3σ) obtained by differential pulse voltammetry (DPV) was 22.0 nmol L(-1). DPV was used for simultaneous determination of 6-TG, uric acid (UA) and folic acid (FA) at the modified electrode, and for quantification of 6-TG, UA and FA in some real samples by the standard addition method.     

HPLC法测定人尿中尿酸含量

建立了一种人体尿液中尿酸含量的高效液相色谱测定方法.采用ACE5 AQ亲水色谱柱,pH3.2的乙酸水溶液为流动相,检测波长280nm.尿酸含量在7.1～224.6μg/mL范围内线性关系良好,平均加样回收率为99.7%～100.5%,RSD小于1.4%.将该法用于健康人和肝硬化病人尿液样本的测定,两类样本中尿酸含量无显...     

Joint voltammetric determination of dopamine and uric acid

Electrocatalytic activities of gold particles deposited onto an electrode unmodified and modified with a self-organized monolayer of cystamine in oxidation of dopamine and uric acid were compared. The possibility of joint determination of dopamine and uric acid on an electrode modified with self-organized monolayer of cystamine with gold nanoparticles was examined.     

Electrochemical and peroxidase-catalyzed redox chemistry of 9-Methyl uric acid

The electrochemical and peroxidase/H₂O₂ oxidation of 9-methyl uric acid has been studied over a wide pH range. Electrochemical, spectral, kinetic and analytical results support the view that the electrochemical and enzymic oxidations proceed by virtually identical mechanisms.     

Modification of carbon paste with congo red supported on multi-walled carbon nanotube for voltammetric determination of uric acid in the presence of ascorbic acid

A chemically modified carbon-paste electrode (CPE) is prepared by incorporating congo red (CR) immobilized on multi-walled carbon nanotube (MWCNT). The results show that CR is effectively immobilized on the surface of MWCNT under the ultrasonic agitation in aqueous solution and further incorporating the nafion. The prepared electrode, due to the electrostatic repulsions between the CR and ascorbate anion, is capable to mask the response of the ascorbic acid (AA) completely and provide an effective method for the detection of minor amounts of uric acid (UA) in the presence of high concentrations of AA. On the other hand, an increase in the microscopic area of the electrode by addition of MWCNT together with the electrocatalytic activity caused to a significant enhancement in the voltammetric response to UA. Optimization of the amounts of composite modifier in the matrix of CPE is performed by cyclic and differential pulse voltammetric measurements. The modified electrode shows a linear response to UA in the range of 1.0 × 10⁻⁷–1.0 × 10⁻⁴ M with a detection limit of 1.0 × 10⁻⁸ M. The electrode exhibits excellent accuracies for the determination of UA in the presence of high concentrations of AA (a recovery of 97.6%). The response of the electrode toward sulfhydryl compounds such as cysteine, penicillamine, and glutathione is not considerable. This reveals a good selectivity for the voltammetric response toward UA. The effective electrocatalytic property, ability for masking the voltammetric responses of the other biologically reducing agents, ease of preparation, and surface regeneration by simple polishing together with high reproducibility and stability of the responses make the modified electrode suitable for the selective and sensitive voltammetric detection of sub-micromolar amounts of UA in clinical and pharmaceutical preparations.     

Electrochemical cleavage of DNA in the presence of copper-sulfosalicylic acid complex

Electrochemical cleavage of DNA in the presence of copper-sulfosalicylic acid [Cu(ssal)(2)(2+)] complex was studied. The cleavage was observed in a certain potential region where redox cycling of Cu(ssal)(2)(2+)/Cu(ssal)(2)(+) took place. Cu(ssal)(2)(2+) complex mediate generation of reactive oxygen species from O(2) by the Fenton reaction, these radicals are capable of damaging DNA. The cleaved DNA fragments were separated by high-performance liquid chromatography (HPLC). The experimental results indicated that the method for electrochemical cleavage of DNA by Cu(ssal)(2)(2+) complex was simple and efficient.     

Uricase based methods for determination of uric acid in serum

The most common methods for determination of uric acid in serum are based on the use of the enzyme uricase. Uric acid is enzymatically oxidized by oxygen to produce hydrogen peroxide, allantoin, and carbon dioxide. The four most often applied uricase methods are critically compared in this review.