Quinoprotein glucose dehydrogenase modified carbon paste electrode for the detection of phenolic compounds

The development of an amperometric biosensor for the determination of phenolic compounds is described, using quinoprotein glucose dehydrogenase. The enzyme is integrated into carbon paste and its ability to donate electrons to oxidized phenolic compounds during glucose oxidation is exploited. The sensor response is based on electrochemical oxidation of the phenolic compound followed by its enzymatic regeneration when the bulk solution contains glucose and the electrode is potentiostated at +500 mV (vs. Ag/AgCl/0.1 mol/L KCl). As the result of the catalytic analyte regeneration the electrodes offer very sensitive measurements of redox species like p-aminophenol and hydroquinone and catecholamines such as epinephrine, norepinephrine, and dopamine. The sensor performance is characterized for the different substrates. Highest sensitivity is achieved for p-aminophenol which could be determined at sub-nanomolar level.     

镓(Ⅲ)-茜素氨羧络合剂在碳糊电极上的阳极吸附伏安法研究及应用

研究了镓(Ⅲ)-茜素氨羧络合剂(ALC)在碳糊电极上的阳极吸附伏安行为,并以此建立了一种高灵敏度、高选择性测定镓的吸附伏安法.在0.12 mol/L HAc-NaAc-0.24 mol/L邻苯二甲酸氢钾底液(pH 4.5)中,-0.10 V (vs.SCE) 富集90 s (或180 s),以250 mV/s扫速线性扫描至0.90 V, Ga3+-ALC在碳糊电极上产生灵敏的与ALC的峰电位相差近230 mV的吸附氧化峰,其二次导数峰电流与镓浓度在5.0×10-10～8.0×10-7 mol/L范围内呈线性关系;富集240 s检出限达3.0×10-10 mol/L(S/N=3).探讨了电极反应机理.该法用于粮食样品中镓的测定,结果满意.     

Effects of pretreatments and modifiers on electrochemical properties of carbon paste electrodes

The electrochemical properties of carbon paste electrodes (CPEs), including unmodified and modified with protein and polycations, were investigated by impedance spectroscopy (IS) using ferricyanide and ferrocene monocarboxylic acid (FcMA) as redox probes. Various electrochemical pretreatments were applied to the unmodified CPE. The heterogeneous charge transfer rate constant of ferro/ferricyanide couple is enhanced by 2 to 10 times compared with that obtained at untreated electrodes. It was found that for ferricyanide the more suitable pretreatments are successive cyclic voltammetric scans, cathodization and a square wave-like stepping rather than high-potential anodization. However, the pretreatment only exhibits a slight effect on the kinetics of FcMA. At the CPEs containing modifier, the electron transfer rate of the redox couple depends more on the pH of electrolyte solution if ferro/ferricyanide is used. The results can be explained by the differently charged states of the CPEs that were caused by the protonation or deprotonation of the modifiers in various pH solutions and demonstrate the importance of the electrostatic interaction on the kinetics of the highly polar species such as ferricyanide. The different adsorptive behavior of ferricyanide and FcMA is also discussed.     

Inorganic—Organic Hybrid 18—Molybdodiphosphate Nanoparticles Bullk—modified Carbon Paste Electrode and Its Electrocatalysis

A kind of inorganic‐organic hybrid 18‐molybdodiphosphate nanoparticles ([(C₄H₉)₄N]₆P₂Mo₁₈Q₆₂·4H₂O) was firstly used as a bulk‐modifier to fabricate a three‐dimensional chemically modified carbon paste electrode (CPE) by direct mixing. The electrochemical behavior of the solid nanoparticles dispersed in the CPE in acidic aqueous solution was characterized by cyclic and square‐wave voltammetry. The hybrid 18‐molybdodiphosphate nanoparticles bulk‐modified CPE (MNP‐CPE) displayed a high electrocatalytic activity towards the reduction of nitrite, bromate and hydrogen peroxide. The remarkable advantages of the MNP‐CPE over the traditional polyoxometalates‐modified electrodes are their excellent reproducibility of surface‐renewal and high stability owing to the insolubility of the hybrid 18‐molybdodiphosphate nanoparticles.     

A selective voltammetric method for uric acid detection at Nafion(R)-coated carbon paste electrodes

A square-wave voltammetric method together with Nafion®-coated carbon paste electrodes were used for the selective determination of uric acid in the presence of a high concentration of ascorbic acid. Since the oxidation potential of uric acid is about 200 mV more positive than that of ascorbic acid at the Nafion®-coated carbon paste electrode, the selectivity can be greatly improved simply by applying an electrolysis potential of +0.4 V vs. Ag/AgCl where only ascorbic acid is oxidised. The acceptable tolerance of ascorbic acid concentration for the determination of uric acid is as high as 1.5 mM. With 30 s of electrolysis time, a linear calibration curve is obtained over the 0–50 μM range in 0.05 M citrate buffer solution, pH 4.0, with slope (μA/μM) and correlation coefficient of 0.34 and 0.9984, respectively. The detection limit (3σ) is 0.25 μM. The practical analytical utility is illustrated by selective measurements of uric acid in human urine without any preliminary treatment.     

An ionic liquid-type carbon paste electrode and its polyoxometalate-modified properties

The replacement of a non-conductive organic binder with a conductive room temperature ionic liquid in fabricating carbon paste electrode has been made. This new electrode due to its enhanced conductivity presented very large current response from electroactive substrates. The novel carbon paste electrode was bulk-modified via the uniform dispersion of Keggin-type phospho polyoxomolybdate (PMo₁₂) in bulky carbons, which possessed excellent electrocatalytic activity for the reduction of nitrite. The pronounced multi-electron catalytic ability was ascribed to the used hydrophobic ionic liquid which constructed an excellent charge-transfer bridge in the bulk of carbon paste electrode, thus facilitated the intake of electrons from reduced PMo₁₂ mediators. In view of their prominent properties, the carbon paste electrode using ionic liquid binder and its bulk-modified electrode take on good prospects of the application in physical chemistry and electroanalytical chemistry fields.     

碳糊电极阳极吸附伏安法测定大黄酸

在pH4.2的HAc-NaAc底液中,大黄酸在碳糊电极(CPE)上有一灵敏的吸附氧化峰,峰电位为1.14V(vs.SCE)。该氧化峰的二阶导数峰电流与大黄酸的浓度在8.0×10-9~8.0×10-7mol/L(富集120s)范围内呈良好的线性关系(r=0.998),检出限为2×10-9mol/L(S/N=3,富集180s)。探讨了大黄酸在CPE上的伏安性质和电极反应机理,并将本法应用于中药大黄中的大黄酸的测定,结果良好。     

An Inexpensive Biosensor for Uric Acid Determination in Human Serum by Flow‐Injection Analysis

An inexpensive and easy to construct miniaturized biosensor is described for the determination of uric acid in biological fluids. The amperometric biosensor was prepared by using a carbon paste electrode prepared with uricase from Arthrobacter globiforms and tetracyanoquinodimethane as electron transfer mediator. When incorporated into a flow‐injection system it was enabled to perform 50 measurements/h of uric acid in the analytical range of 1–100 μmol dm^?3 with a relative standard deviation of 0.20% (n=14). The system was applied to human serum samples analysis providing good data correlation with those obtained by the reference spectrophotometric method. A linear relationship AM (μmol dm^?3)=1.02 (±0.05) SP (μmol dm^?3) ?0.12 (±0.13) was obtained evidencing the absence of significant error. The constructed biosensor was successfully used for at least four months (250 assays) with only a 13% of decrease in the enzymatic activity.     

聚酰胺修饰碳糊电极测定槲皮素的研究

用聚酰胺修饰碳糊电极在ｐＨ３６０的Ｂｒｉｔｏｎ－Ｒｏｂｉｎｓｏｎ缓冲溶液中，将槲皮素开路富集一定时间后，从０４５Ｖ（ｖｓ．Ａｇ／ＡｇＣｌ）向阴极化扫描至－０５５Ｖ获得Ｉ－Ｅ曲线。槲皮素的峰电位为０１８Ｖ。峰电流与槲皮素浓度在１０～４００μｍｏｌ／Ｌ范围内呈良好的线性关系。所拟定方法用于芦丁水解产物测定，结果满意。     

Chemical species produced in the reaction between ethanedial (glyoxal) and 5-amino-1,10-phenanthroline and their iron(II) complexes: electrochemical studies and analytical applications

The cyclic voltammetric behavior of carbon paste electrodes modified by direct admixing with the products of the reactions between ethanedial (glyoxal) and 5-amino-1,10-phenanthroline at 100°C and that of their iron(II) complexes is reported. The ligand(s) produced in absence of iron(II) are able to complex iron(II) and copper(II) ions reversibly, but other ions such as nickel(II), cobalt(II), cadmium(II) and manganese(II), if complexed, show no electrochemical activity. Admixing with the products of the reaction in the presence of excess of iron(II) ion, because of high insolubility and fast electron exchange, produces surfaces useful for amperometric detection in continuous-flow systems. The voltammetric and amperometric behavior in the presence of HSO^?₃ ions is reported in order to illustrate this application.