Electrocatalytic Determination of 6‐Tioguanine at a p‐Aminophenol Modified Carbon Paste Electrode

A p‐aminophenol modified carbon paste electrode (p‐APMCPE) was constructed for determination of an anticancer drug 6‐thioguanine (6‐TG). The cyclic voltammogram showed that the electrocatalytic oxidation of 6‐TG at the surface of p‐APMCPE occurs at a potential about 840 mV less positive than at an unmodified electrode. Square‐wave voltammetry results presented that the electrocatalytic oxidation peak currents of 6‐TG in pH 9.0 had two linear dynamic ranges in the range of 0.2 to 8.0 and 8.0 to 350.0 μM 6‐TG with a detection limit of 0.08 μM. The kinetic parameters such as electron transfer coefficient (α) and rate constant were determined for the chemical reaction between 6‐TG and p‐aminophenol. Finally, this method was evaluated for the determination of 6‐TG in 6‐thioguanine tablets and urine samples.     

A Selective and Sensitive Method for Simultaneous Determination of Traces of Paracetamol and p‐Aminophenol in Pharmaceuticals Using Carbon Ionic Liquid Electrode

A reliable and simple electrochemical method has been proposed for the simultaneous determination of paracetamol (PAR) and p‐aminophenol (PAP) in pharmaceutical formulations. The oxidation and reduction peak potentials in cyclic voltammetry (CV) for PAR on carbon ionic liquid electrode (CILE) were occurred at 370 and 225 mV vs. Ag/AgCl, respectively at pH 7.0, while those for PAP on CILE appeared at 128 mV and 68 mV, respectively at the scan rate of 0.05 V s^?1. In comparison to the conventional carbon paste electrode, the apparent reversibility and kinetics of the electrochemical reactions of PAR and PAP were significantly improved on CILE. In differential pulse voltammetric technique, the peak potentials for PAR and PAP appeared at 345 and 130 mV, respectively, with the peak separation of 215 mV, sufficient for their simultaneous determination in samples containing these two species. The proposed method was used for simultaneous determination of PAR and PAP in tablets. PAR and PAP can be determined in the ranges of 2.0×10^?6–2.2×10^?3 M and 3.0×10^?7–1.0×10^?3 M, with the detection limits of 5.0×10^?7 and 1.0×10^?7 M (calculated by 3σ), respectively. The relative standard deviations for the determination of PAR and PAP were less than 2%.     

Direct Determination of Phosphite in Fertilizers by Flow‐Injection Amperometry

A sensor based on graphite electrode modified with palladium‐platinum‐palladium film is proposed for phosphite determination by flow‐injection amperometry. The modified electrode was prepared by a sequential cathodic deposition of Pd, Pt and Pd on a graphite electrode from 0.5% m/v PdCl₂+28% m/v NH₄OH and 2% m/v H₂PtCl₆+10% v/v H₂SO₄ solutions. After suitable conditioning, the electrode showed catalytic activity for phosphite oxidation when 0.15 V was applied. The proposed system handles approximately 50 samples per hour (0.01–0.05 mol L^?1 Na₂HPO₃; R²=0.9997), consuming ca. 70 μL of sample per determination. The limit of detection and amperometric sensibility were 5×10^?4 mol L^?1 and 1.5 mA L mol^?1, respectively. The proposed method was applied to analysis of fertilizer samples without pre‐treatment. Results are in agreement with those obtained by spectrophotometry and titrimetry at 95% confidence level and good recoveries (96–109%) of spiked samples were found. Relative standard deviation (n= 12) of a 0.01 mol L^?1 Na₂HPO₃ sample was 2%. The useful lifetime of modified electrode was around 220 determinations. For routine purposes it means that this electrode can be continuously used for 5 hours.     

纳米PbO2修饰电极安培检测器流动注射法快速测定化学需氧量

采用以纳米PbO₂修饰电极为工作电极的安培检测器,用流动注射法快速检测水体中的化学需氧量(COD).根据纳米PbO₂修饰电极催化氧化电流的大小测定样品的COD值,在50-1 200 mg/L COD的范围内,电流响应与标准水样中的COD_Cr值呈线性关系,检出限为20 mg/L.该法不需对水样进行预处理,不使用有毒试剂,无二次污染,具有快速、简便、进样量少及工作电极使用寿命长等优点,与COD_Cr国家标准分析法对比具有较好的相关性.     

Flow Injection Analysis of Chloramphenicol by Using a Disposable Wall‐Jet Ring Disk Carbon Electrode

A preanodized screen‐printed ring disk carbon electrode was applied to the determination of chloramphenicol (Ph? NO₂, CAP) by flow injection analysis (FIA). By setting up the first irreversible reduction reaction of Ph? NO₂ to Ph? NHOH at the disk electrode, the following reversible oxidation of hydroxylamine (Ph? NHOH) to the nitroso (Ph? NO) derivative can be monitored/collected at the ring electrode for CAP analysis. The interference from dissolved oxygen and others can thus be avoided by using this approach and precise CAP determination can be easily performed by FIA under aerobic conditions. Preanodization treatment helps to lower the overpotential of the electrochemical reaction of CAP and favors the selective detection in aqueous medium. Under the optimum conditions, ten repetitive determinations at 1 μM and 10 μM CAP resulted in relative standard deviations of less than 4%, indicating good reproducibility of the system. A linear calibration range of 0.1–20 μM with a detection limit of 0.074 μM (S/N=3) was obtained. Veterinary pharmaceutics were finally analyzed by this sensor to validate its practical applicability.     

Flow Injection Analysis of Ascorbyl Glucoside in Cosmetics by a Disposable Printed‐Circuit Board Waste Modified Electrode

Ascorbyl glucoside, i.e., ascorbic acid 2‐glucoside (AA‐2G), is anew type of stable vitamin C derived compound used in many cosmetic skin‐lightening formulations, but rarely studied in the literature. In this study, a screen printed electrode modified with copper‐enriched printed circuit‐board waste (designated as Cu_PCB/SPE) was applied to study the electrochemical characteristics of AA‐2G. Cyclic voltammogram of the Cu_PCB/SPE showed an electrocatalytic oxidative feature at ?0.6 V vs. Ag/AgCl in 0.15 M NaOH solution. Flow injection analysis coupled with the Cu_PCB/SPE was further developed for sensitive AA‐2G determination. The calibration plot was linear in the window of 2.5–160 ppm with slope and regression coefficient of 0.0169 μA/ppm and 0.9971, respectively. The detection limit (S/N = 3) was 0.247 ppm. Real sample analysis was demonstrated for different skin‐lightening cosmetic products with appreciable results.     

Flow Injection Analysis of Lactate and Lactate Dehydrogenase Using an Enzyme Membrane in Conjunction with a Modified Electrode

Abstract

A modified electrode for H₂O₂ oxidation, consisting of Pd/Au sputtered on carbon was covered with a lactate oxidase membrane and used in a FIA manifold for selective determination of lactate. The linear range was 0.01-3 mM lactate and up to 200 samples per hour were measured with a relative standard deviation of 1%. Interferences from ascorbic acid and NADH were small because of the low potential of the modified electrode. The lactate oxidase membrane electrode was also used for measurement of lactate dehydrogenase activity using direct injection of the sample into a carrier stream containing pyruvate and NAD⁺.     

Electrocatalytic Oxidation of Some Carbohydrates by Nickel/Poly(o‐Aminophenol) Modified Carbon Paste Electrode

This study investigates the electrocatalytic oxidation of glucose and some other carbohydrates on nickel/poly(o‐aminophenol) modified carbon paste electrode as an enzyme free electrode in alkaline solution. Poly(o‐aminophenol) was prepared by electropolymerization using a carbon paste electrode bulk modified with o‐aminophenol and continuous cyclic voltammetry in HClO₄ solution. Then Ni(II) ions were incorporated to electrode by immersion of the polymeric modified electrode having amine group in 1 M Ni(II) ion solution. Cyclic voltammetric and chronoamperometric experiments were used for the electrochemical study of this modified electrode; a good redox behavior of Ni(OH)₂/NiOOH couple at the surface of electrode can be observed, the capability of this modified electrode for catalytic oxidation of glucose and other carbohydrates was demonstrated. The amount of α and surface coverage (Γ*) of the redox species and catalytic chemical reaction rate constant (k) for each carbohydrate were calculated. Also, the electrocatalytic oxidation peak currents of all tested carbohydrates exhibit a good linear dependence on concentration and their quantification can be done easily.     

Decomposition and Detection of Hydrogen Peroxide Using δ‐MnO2 Thin Film Electrode with Self‐Healing Property

A thin film of δ‐type MnO₂ grown cathodically has been investigated with respect to the ability toward anodic decomposition of H₂O₂ and durability. With polarization at less positive potentials than +0.4 V vs. Ag/AgCl, the film was dissolved exclusively as a result of reduction of Mn⁴⁺ sites in the oxide by H₂O₂ to soluble Mn²⁺. At +0.9 V, MnO₂ remained unchanged and decomposed H₂O₂ in solution. At +0.8 V, the film was once dissolved in the initial stage; however, it was self‐healed via reoxidation of the liberated Mn²⁺ ions. Amperometric flow‐injection analysis of H₂O₂ was carried out with the δ‐MnO₂ film.     

壁喷电池在流动注射阳极溶出伏安法中的应用

在流动注射阳极溶出伏安法中应用壁喷电池,探讨了非稳定态电积过程的溶出峰电流理论方程,预言了峰电流正比于R~(3/4)(R为工作电极半径),并对有关参数进行了实验验证。对5×10~(-7)mol/L Cd(Ⅱ)连续测定40次,表明相对标准偏差为0.94％。     

流动注射掺杂普鲁士蓝碳糊电极测定过氧化氢

在化学法制得普鲁士蓝(PB)粉末的基础上,用固体石蜡作粘合剂,将PB粉末和石墨粉按一定比例充分混合,制得掺杂PB的碳糊电极(PBCPE)。研究了该修饰电极的制备,电化学性质及对H2O2的电催化作用。该修饰电极在0.5mol/L的KCl底液中进行循环伏安实验,于0.2V(vs.SCE)附近出现一对氧化还原峰,扫速为30mV/s时,峰电位差67mV,重现性良好。采用流动注射进样,基于PBCPE电极成功实现了恒电位快速检测医用消毒水中H2O2的浓度。最佳检测电位为-0.3V,进样频率为120次/小时。响应电流与H2O2的浓度在0.08～3.2mmol/L范围内呈良好的线性关系,线性相关系数为0.9994,检出限为2.4×10-6mol/L(S/N=3)。     

A Voltammetric Sensor Based on Modified Multiwall Carbon Nanotubes for Cysteamine Determination in the Presence of Tryptophan Using p‐Aminophenol as a Mediator

Determination of cysteamine and tryptophan is described by electrochemical methods using p‐aminophenol‐multiwall carbon nanotubes paste electrode. Cysteamine and tryptophan in mixture can each be measured independently from each other with a potential difference of 600 mV. The results showed that the electrocatalytic currents increased linearly with cysteamine and tryptophan concentrations over the ranges 0.5–300 µmol L^?1 and 10.0–650 µmol L^?1, respectively. The detection limits for cysteamine and tryptophan are found to be 0.14 and 5.9 µmol L^?1, respectively. The proposed method is successfully employed for the determination of cysteamine in both capsule and urine samples.     

Electrocatalytic Oxidation and Voltammetric Determination of Hydrazine on the Tetrabromo‐p‐Benzoquinone Modified Carbon Paste Electrode

The electrochemical properties of hydrazine studied at the surface of a carbon paste electrode spiked with p‐bromanil (tetrabromo‐p‐benzoquinone) using cyclic voltammetry (CV), double potential‐step chronoamperometry and differential pulse voltammetry (DPV) in aqueous media. The results show this quinone derivative modified carbon paste electrode, can catalyze the hydrazine oxidation in an aqueous buffered solution. It has been found that under the optimum conditions (pH 10.00), the oxidation of hydrazine at the surface of this carbon paste modified electrode occurs at a potential of about 550 mV less positive than that of a bar carbon paste electrode. The electrocatalytic oxidation peak current of hydrazine showed a linear dependent on the hydrazine concentrations and linear analytical curves were obtained in the ranges of 6.00×10^?5 M–8.00×10^?3 M and 7.00×10^?6 M–8.00×10^?4 M of hydrazine concentration with CV and differential pulse voltammetry (DPV) methods, respectively. The detection limits (3σ) were determined as 3.6×10^?5 M and 5.2×10^?6 M by CV and DPV methods. This method was also used for the determination of hydrazine in the real sample (waste water of the Mazandaran wood and paper factory) by standard addition method.     

流动注射分析用新型钆离子电极

功能高分子为活性材料,加热压片,制成新型钆电极。其性能较PVC式钆离子选择电极为优。取钆电极膜片制成流通式钆电极,与流动注射仪联用,测得电极斜率59mV,与静态响应相似。每次进样500μl,测定频率每小时60～100次。操作简单,重现性好。     

Flow Injection Analysis of Iodate Reduction on PEDOT Modified Electrode

Poly‐(3,4‐ethylenedioxythiophene) (PEDOT) films were electrodeposited by cyclic voltammetry on glassy carbon electrode at different anodic potentials in the range of 1.0–1.5 V (Ag/AgCl) and its electrocatalytic properties towards reduction of iodate were reported. The effect of the pH of the solution on the response of PEDOT electrode towards iodate also studied. The modified electrode was employed successfully as an amperometric sensor for iodate in a flow injection apparatus. The repeatability of the method for 14 injections of a μM iodate solution was 7%. Interference from other oxidant anions such as nitrate was not noticeable, whereas bromate, chlorate and nitrite interfere at slight levels.     

Flow Injection Analysis of Maleic Hydrazide Using an Electrochemical Sensor Based on Palladium‐Dispersed Carbon Paste Electrode

A new analytical methodology for the electrochemical detection of the herbicide maleic hydrazide (3,6‐dihydroxypyridazine) by flow injection analysis is presented. This method is supported by the novel application of a palladium‐dispersed carbon paste electrode as an amperometric sensor for this herbicide. Maleic hydrazide shows anodic electrochemical activity on carbon‐based electrodes (glassy carbon or carbon paste electrodes) in all the pH range. This electrochemical activity is enhanced using metal‐dispersed carbon paste electrodes, especially at Pd‐dispersed CPE which displays good oxidation signals at 690 mV (0.050 M phosphate buffer pH 7.0), 140 mV lower than at unmodified electrodes. Under the optimized conditions, the electroanalytical performance of Pd‐dispersed CPE in flow injection analysis was excellent, with good reproducibility (RSD 3.3%) and a wide linear range (1.9×10^?7 to 1.0×10^?4 mol L^?1). A detection limit of 1.4×10^?8 mol L^?1 (0.14 ng maleic hydrazide) was obtained for a sample loop of 100 μL at a fixed potential of 700 mV in 0.050 M phosphate buffer solution at pH 7.0 and a flow rate of 2.0 mL min^?1. The proposed method was applied for the maleic hydrazide detection in natural drinking water samples.     

A PVC/TTF‐TCNQ Composite Electrode for Use as a Detector in Flow Injection Analysis

A new polyvinyl chloride (PVC)/tetrathiafulvalene‐tetracyanoquinodimethane (TTF‐TCNQ) composite electrode was prepared and tested for electroanalytical performance. Different PVC/TTF‐TCNQ–graphite proportions were used in order to obtain the best possible detector for accommodation in a wall‐jet electrochemical cell of use in flow injection analysis. A PVC/TTF‐TCNQ w/w ratio of 1/10 provided the best results in terms of sensitivity, coefficients of variation and mechanical resistance. The voltammetric and flow‐injection amperometric detection responses of the electrode to ascorbic acid (AA) were measured and compared with those of a PVC–graphite electrode. The resulting electrode provided good electrode kinetics with a low background current and a relatively reproducible signal. In addition, the electrode can be readily prepared and its surface readily renewed.     

聚2-吡啶甲酸修饰电极伏安法测定多巴胺

用循环伏安法制备了聚２－吡啶甲酸修饰玻碳电极，研究了神经递质多巴胺（ＤＡ）在该聚合物薄膜修饰电极上的电化学行为。实验结果表明，在ｐＨ７．０的磷酸盐缓冲溶液中，ＤＡ在该电极上的线性范围为１．０×１０－７～１．０×１０－５ｍｏｌ／Ｌ。该修饰电极对抗坏血酸（ＡＡ）无响应，从而可有效消除其对ＤＡ测定的干扰。     

Flow‐Injection Pulsed‐Amperometric Determination of Free Glycerol in Biodiesel at a Gold Electrode

This work reports the highly‐sensitive amperometric determination of free glycerol in biodiesel at a gold electrode adapted in a flow‐injection analysis (FIA) cell. The amperometric method involved the continuous application of three sequential pulses to the working electrode (+250 mV, +700 mV, and ?200 mV, for 100 ms each). This sequence of potential pulses eliminated electrode passivation and dramatically increased the analytical signal. The proposed FIA‐amperometric method presented low relative standard deviation between injections (1.5 %, n=15), high analytical frequency (85 h^?1), satisfactory recovery values (93–118 %) for spiked samples, wide linear range (from 1 to 300 µmol L^?1), and low detection limit (0.5 µmol L^?1).