Simple and rapid method for the determination of uric acid-independent antioxidant capacity

Determination of the relative contribution of uric acid level increases to the total measured antioxidative activity could be very useful for testing antioxidative products and their effect on human health. The aim of this report is to present a simple spectrophotometric method that combines the measurement of total antioxidative capacity of a sample by ferric reducing/antioxidative power (FRAP) assay, with the uricase-reaction (specific elimination of uric acid), in order to establish and correct for the contribution of uric acid in FRAP values. We measured FRAP values, with (uric acid-independent antioxidant capacity, TAC-UA) and without (total antioxidant capacity, TAC) uricase treatment, and expressed it as μmol/L of uric acid equivalents. In such way, it was possible to determine both total and uric acid-independent antioxidant capacity, plasma uric acid (UA, as the difference between TAC and TAC-UA), and the ratio of the uric acid in total antioxidant capacity (UA/TAC).     

A poly(3-acetylthiophene) modified glassy carbon electrode for selective voltammetric measurement of uric acid in urine sample

A reliable and reproducible method for the determination of uric acid in urine samples has been developed. The method is based on the modification of a glassy carbon electrode by 3-acetylthiophene using cyclic voltammetry. The poly(3-acetylthiophene) modified glassy carbon electrode showed an excellent electrocatalytic effect towards the oxidation of uric acid in 0.1 m phosphate buffer solution (PBS) at pH 7.2. Compared with a bare glassy carbon electrode (GCE), an obvious shift of the oxidation peak potential in the cathodic direction and a marked enhancement of the anodic current response for uric acid were observed. The poly(3-acetylthiophene)/GCE was used for the determination of uric acid using square wave voltammetry. The peak current increased linearly with the concentration of uric acid in the range of 1.25 x 10(-5)-1.75 x 10(-4) M. The detection limit was 5.27 x 10(-7) M by square wave voltammetry. The poly(3-acetylthiophene)/GCE was also effective to determine uric acid and ascorbic acid in a mixture and resolved the overlapping anodic peaks of these two species into two well-defined voltammetric peaks in cyclic voltammetry at 0.030 V and 0.320 V (vs. Ag/AgCl) for ascorbic acid and uric acid, respectively. The modified electrode exhibited stable and sensitive current responses toward uric acid and ascorbic acid. The method has successfully been applied for determination of uric acid in urine samples.     

泌尿系统尿酸结石研究中的化学基础

尿酸结石是指尿酸及其盐在泌尿系统的异常矿化和积聚。本文从尿酸结石研究中涉及的化学问题入手,讨论了pH、过饱和度、尿大分子抑制剂和基因突变等方面对尿酸结石形成的分子机理,从抑制尿酸结石成核、生长和聚集的角度,讨论了尿酸结石的化学模型和动物实验模型。     

基于氢键作用的金纳米粒子比色法检测尿酸

尿酸含量高可使人产生痛风等疾病,尿酸的测定是临床检测重要的生化指标之一。金纳米粒子比色法检测尿酸实验联系实际生活,将科研前沿和教学内容有机结合起来,可以激发学生的学习兴趣,加深学生对经典理论的理解,增加学生对科研前沿的了解。本实验利用金纳米粒子吸光系数高的特点,通过尿酸与三聚氰胺反应后,抑制三聚氰胺诱导的金纳米粒子聚集,从而达到检测尿酸的目的。随着溶液中尿酸浓度的增加,溶液颜色由蓝变红,差别明显,视觉效果好,容易分辨。     

A Uricase Method for the Peak Identification of Uric Acid Appeared in a Liquid Chromatogram Amperometrically Monitored

Abstract

A uricase method for the peak identification of uric acid appeared in a liquid chromatogram monitored by aid of an electrochemical detector has been developed. Uricase (EC 1.7.3.3, from Candida utilis) catalyzes the conversion of uric acid to allantoin. We have found that uric acid can be oxidized under the chromatographic conditions employed in this study, whereas allantoin cannot be oxidized. The complete disappearance of a uric acid peak in a chromatogram of a biological sample after the uricase treatment indicates that the uric acid peak does not contain any other electroactive components. We observed the complete disappearance of the uric acid peaks in the chromatograms of human serum and gastric body.     

全血尿酸生物传感器的研制及临床应用

研制了一种利用全血来测试尿酸含量的安培型生物传感器。采用铁氰化钾作为媒介体,将尿酸氧化酶固定在羧甲基纤维素钠处理过的碳电极表面,研制成一种尿酸生物传感器。该传感器在恒电位0.3V和尿酸氧化酶的催化作用下,使被检测物尿酸氧化,铁氰化钾还原,在电极表面产生氧化-还原峰,利用安培法可对尿酸进行间接测定。该传感器经临床测试,尿酸的测定范围可达25~200mg/L,10s内即可达到稳态电流,测试结果的线性范围较好,相关系数为0.9987。另外,尿酸传感器具有好的抗干扰性,测试精度高、重复性好,RSD<2%。     

The analysis of uric acid in urine using microchip capillary electrophoresis with electrochemical detection

Clinical studies have linked irregular concentrations of uric acid in urine to several diseases. Conventional methods for the measurement of uric acid are however temperature-dependent, expensive, and require labile reagents. The miniaturization of analytical techniques, specifically capillary electrophoresis, offers an ideal alternative for clinical analyses such as uric acid determination. The added benefits include reduced reagent and analyte consumption, decreased maintenance costs, and increased throughput and portability. A microchip capillary electrophoresis-electrochemical system for the analysis of uric acid in urine is described. The poly(dimethylsiloxane) (PDMS)/glass microchip utilizes amperometric detection via an off-chip platinum working electrode. Linear responses from 1 to 165 microM and 15 to 110 microM were found for dopamine and uric acid, respectively. The limit of detection for both compounds was 1 microM. Once characterized, the system was used to measure the concentration of uric acid in a dilute urine sample in less than 30 s. The measured uric acid concentration was verified with the uricase reaction and found to be acceptable. Six additional urine samples were evaluated with the microchip device and the uric acid concentration for each sample was found to be in the expected clinical concentration range.     

Graphene Doped Molecularly Imprinted Electrochemical Sensor for Uric Acid

A highly sensitive uric acid molecularly imprinted electrochemical sensor was prepared by using graphene doped chitosan as the functional matrix and uric acid as the template molecule; a electrodeposition technique was used to form a controllable graphene–chitosan–uric acid composited film on glassy carbon electrode whose uric acid was removed via electrochemical induce elution. Under the optimized preparation and detection conditions, the detection sensitivity of uric acid at graphene doped molecularly imprinted sensor was improved significantly compared with the undoped molecularly imprinted sensor. The mechanisms of sensitivity enhancement were studied by a.c. electrochemical impedance, adsorption model, and chronocoulometry. The observations suggest the effect of sensitivity enhancement resulted from magnified surface area and good electronic conduction of graphene. Additionally, the developed sensor exhibited specific recognition to uric acid against the competitors which consisted of structure liked substances and coexisting interference in blood serum.     

Voltammmetric Determination of Uric Acid in the Presence of Ascorbates Using Overoxidized Polypyrrol

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Simultaneous Determination of Uric Acid and Ascorbic Acid Using Edge Plane Pyrolytic Graphite Electrodes

Edge plane pyrolytic graphite electrodes have been applied for the determination of uric acid and ascorbic acid. The separate determination of uric acid was found to produce three linear ranges from 100 nM to 3400 μM with a detection limit of 30 nM found to be possible. Uric acid detection was also explored in the presence of 200 μM ascorbic acid where a detection limit of 52 nM was found to be possible. The detection of ascorbic acid in the presence of uric acid was also explored over three linear ranges of ascorbic acid with a limit of detection of 80 nM. Last the simultaneous determination of both uric acid and ascorbic acid is investigated over the range 100 nM to 1000 μM where detection limits of 50 nM and 120 nM were obtained respectively. Analysis of uric acid in a growth tissue medium was found to be successful, confirming the applicability of the methodology to real matrices. This protocol is shown to provide low detection limits, easy handling (no electrode modification), good voltammetric peak separation of uric acid and ascorbic acid and a wide linear dynamic range.     

Simultaneous detection of epinephrine,uric acid,and ascorbic acid with graphene-modified electrode

A graphene-modified glassy carbon electrode was obtained via drop-casting method and applied to the simultaneous detection of epinephrine, uric acid, and ascorbic acid by cyclic voltammetry in a phosphate buffer solution (pH 3.0). The oxidation potentials of epinephrine, uric acid, and ascorbic acid were 0.484, 0.650, and 0.184 V at the graphene-modified glassy carbon electrode, respectively. The peak separation between epinephrine Pand uric acid, epinephrine and ascorbic acid, and uric acid and ascorbic acid was about 166, 300, and 466 mV, respectively. So, this graphene-modified electrode can be used for simultaneous determination of each component in a mixture.     

Electrochemical behavior of uric acid and epinephrine at an electrochemically activated glassy carbon electrode

A pretreated glassy carbon electrode by electrochemical activation has been proposed for simultaneous investigation and determination of epinephrine and uric acid by differential pulse voltammetry. This pretreated glassy carbon electrode exhibits a potent and persistent electron-mediating behavior followed by well-separated oxidation peaks towards epinephrine and uric acid with a potential difference of 161 mV, which is large enough to determine epinephrine and uric acid individually and simultaneously. Under the optimum condition, the detection limit of epinephrine is 8.9 x 10(-8)mol L(-1) and that of uric acid is 1.6 x 10(-7)mol L(-1). The proposed method was successfully used for the determination of epinephrine and uric acid in real samples with satisfactory results.     

Individual and simultaneous determination of uric acid and ascorbic acid by flow injection analysis

Flow injection methods for the individual and simultaneous determination of ascorbic acid and uric acid are proposed. A spectrophotometer and a miniamperometric detector are connected in sequence. The calibration graphs for uric acid obtained by measuring its absorbance at 293 nm and its current at +0.6 V are linear up to at least 80 and 70 mug/ml, respectively, with an rsd (n = 10) of 1 % for both methods at mid-range concentrations. The calibration graph for ascorbic acid with amperometric detection is linear up to 80 mg/l. with an rsd (n = 10) of 0.8% at 30 mg/l. The simultaneous determination of uric acid and ascorbic acid is based on measurement of the absorbance of uric acid at 393 nm and amperometric determination of both analytes at +0.6 V. The average relative errors of the analysis of binary mixtures of uric acid and ascorbic acid are 2.2 and 4.2%, respectively.     

Separation and simultaneous determination of uric acid and ascorbic acid on a dynamically modified poly(dimethylsiloxane) microchip.

Poly(dimethylsiloxane) microfluidic channels alternately modified by poly(diallyldimethylammonium chloride) and poly(sodium 4-styrenesulfonate) were successfully used to separate uric acid and ascorbic acid. Results show that uric acid and ascorbic acid can be well separated and detected simultaneously in modified microchips coupled with in-channel electrochemical detection. Under the optimal conditions, the linear ranges of uric acid and ascorbic acid were both from 25 to 600 microM, with the correlation coefficients of 0.997 and 0.996, respectively. The detection limits were 8 microM for uric acid and 5 microM for ascorbic acid. Factors influencing separation and detection, including buffer solution, detection potential and separation voltage, were investigated and optimized. In addition, the dependences of the current response on sensitivity and reproducibility were studied, and the stability of the device was also evaluated in detail. This method was successfully used to determine uric acid and ascorbic acid in human urine.     

Voltammetric determination of uric acid by using gold nanotubule electrode

Gold nanotubule membranes were prepared by using electroless deposition of gold within the pores and surfaces of polycarbonate track-etched membranes.And the gold nanotubule membrane was used as an electrode for determination of uric acid in urine samples for the first time.In Britton-Robinson buffer of pH 4.56,uric acid exhibited well-defined differential pulse voltammograms.And the interference between coexistent ascorbic acid and uric acid was overcome owing to the attractive ability of the gold nanotubule electrode to yield a large anodic peak difference ca.0.404 V(vs.SCE).The proposed method was then applied to the determination of uric acid in urine without any pretreatment.     

Titrimetric microdetermination of uric acid and thioglycollic acid by amplification reactions

A simple amplification method for determination of 0.05-2 mg of uric acid or thioglycollic acid has been worked out. It depends on iodine oxidation of the uric acid or thioglycollic acid solutions, removal of the excess of iodine, oxidation of the resulting iodide with bromine, and iodometric titration of the resulting iodate. The coefficient of variation ranges from 0.7 to 2.4% for uric acid and from 0.5 to 1.9% for thioglycollic acid, depending on the amount of the acid.     

Preparation and recognition performance of uric acid-imprinted material prepared with novel surface imprinting technique

Acrylonitrile (AN) was first graft-polymerized on the surfaces of crosslinked polyvinyl alcohol (CPVA) microspheres by initiating of cerium salt, and then the grafted polyacrylonitrile (PAN) was transformed to polyamidoxime (PAO) via amidoximation transform reaction, resulting in the functional microspheres PAO/CPVA. By adopting the novel surface-molecular imprinting technique put forward by us, uric acid molecule-imprinted material MIP-PAO/CPVA was prepared with glutaraldehyde as crosslinking agent The binding character of MIP-PAO/CPVA towards uric acid was investigated in depth with both batch and column methods and using guanine as a contrast substance whose chemical structure is similar to uric acid to a certain extent. The experimental results show that the surface imprinted material MIP-PAO/CPVA has excellent binding affinity (a great binding capacity of 104 mg/g) and high recognition selectivity for the template molecule, uric acid. The selectivity coefficient of PAO/CPVA microspheres (non-imprinted material) for uric acid relative to guanine is only 1.273, displaying no recognition selectivity for uric acid. However, after imprinting, the selectivity coefficient of MIP-PAO/CPVA for uric acid in respect to guanine is remarkably enhanced to 14.00, displaying the excellent recognition selectivity and binding affinity towards uric acid molecules.     

Radicals derived from uric acid and its methyl derivatives in aqueous solution: an EPR spectroscopy and theoretical study

The oxidation of uric and of four N-methyluric acids in aqueous solution was studied by EPR spectroscopy. The primary oxidising radicals react with uric acid and its methyl derivatives by formal hydrogen abstraction from an NH group to yield radical-anions in neutral or moderately basic solutions and the respective radical-dianions in basic media. In the case of uric acid, the radical-trianion was detected at very high pH. The pKa values of the radical-anions were determined to be in the range 9.5-11.2. The pKa of uric acid radical-dianion was estimated to be 13.0. DFT calculations were performed to assign the hyperfine coupling constants and to determine the predominant tautomeric structure of the radicals. The uric acid radical-anion exists as the N1H, N9H tautomer, while in the radical-dianion the N1H structure is the most stable one. The intrinsic acidity of the NH protons both in uric acid and in its radicals seems to follow the order N1H < N9H < N3H.     

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%.