Determination of Caffeine Using a Simple Graphite Pencil Electrode with Square-Wave Anodic Stripping Voltammetry

A simple commercial graphite pencil electrode (GPE) was utilized for monitoring caffeine using the square-wave anodic stripping voltammetry (SWASV) method. This method was applied to determine the caffeine levels in several tea samples, which yielded a relative error of 1% in the concentrations. Caffeine was deposited at 0.0V (vs. Ag/AgCl), then reduced at +1.40V to strip it on the GPE. Optimal experimental conditions for the analysis were found to be as follows: pH value of 9 for the medium; deposition potential of 0.0V; deposition time of 120s; SW frequency of 25Hz; SW amplitude of 45mV, and step potential of 6mV. Given these optimum conditions, a linear range was observed within the concentration of 0500mgL^–1. At caffeine concentrations of 50.0, 250.0, and 500.0mgL^–1, the relative standard deviations in measured concentrations (n=12) were 0.19, 0.09, and 0.11%, respectively. The detection limit was found to be 9.2mgL^–1, which is comparable with the result obtained using a carbon paste electrode, equivalent to 8.2mgL^–1.     

对位叠式循环方波伏安法：Ⅱ.平行催化体系

本文提出平行催化体系的对位叠式循环方波伏安法，并对共作了系统的研究，推导了这一方法的催化电流理论方程，并用验验证这理论的正确性，得到其各脉冲电流皆为同方向，对位叠式循环催化电流相当于将电流叠加４次，而波形不受方波幅度大小的影响，因而灵敏度和分辨率有较大提高，优于其它方波伏安法。     

Simultaneous,Selective and Highly Sensitive Voltammetric Determination of Lead,Cadmium, and Zinc via Modified Pencil Graphite Electrodes

Pencil graphite electrode (PGE) modified with MWCNT and Bi³⁺ (MWCNT/Bi/PGE) was utilized in simultaneous analysis of Pb²⁺, Cd²⁺, and Zn²⁺. Surface and electrochemical characteristics of MWCNT/Bi/PGE were investigated via SEM, cyclic voltammetry, electrochemical impedance spectroscopy, and FTIR measurements. Even though modification with MWCNT did not improve the electroactive surface area, it significantly decreased the charge transfer resistance. Furthermore, modification with Bi³⁺ significantly increased the sensitivity. Finally, MWCNT/Bi/PGE exhibited the highest sensitivity and reproducibility compared to PGE and PGE modified with only MWCNT. MWCNT/Bi/PGE provided LOD values of 0.27, 0.43, and 1.63 μg L⁻¹, and linear ranges of 1–80, 5–80, and 10–80 μg L⁻¹ for Pb²⁺, Cd²⁺, and Zn²⁺, respectively. Proposed modification method offers effective electroanalytical performance with low time consumption and cost for the analyst.     

方波伏安法测定酚酞片含量

研究了酚酞在0.5 mol/L氨水-氯化铵缓冲溶液(pH 10)介质中汞膜电极上的电化学行为,并依此建立了酚酞含量的方波伏安法测定.酚酞于-0.98 V(VS.Ag/AgCl)处出现一灵敏的阴极还原峰,峰高与酚酞的浓度在3.0×10-7-5.0×10-5mol/L范围内有良好的线性关系.方法的最低检出限为1.0×10-7mol/L,方法用于酚酞片中酚酞含量的测定,结果满意.     

对位叠式循环方波伏安法：Ⅰ.简单可逆电极体系

本文提出叠式循环方波伏安法和对位叠式循环方波伏安法，对简单可逆电极体系的理论作了推导和验证，经对各种电流的比较，发位叠式循环方波伏安法有较多的优点。较之其它方波伏安法灵敏。     

络合吸附催化循环叠式方波伏安法

对受前行化学反应控制的络合吸附催化体系循环叠式方波伏安法进行了理论推导和实验验证，讨论了电流的特性。结果表明，对于络合吸附催化体系的测定，循环叠式方波伏安法的灵敏度比现行方波伏安法高约２５倍。     

Square Wave Cathodic Adsorptive Stripping Voltammetric Determination of the Anticancer Drugs Flutamide and Irinotecan in Biological Fluids Using Renewable Pencil Graphite Electrodes

A sensitive electrochemical method based on square wave cathodic adsorptive stripping voltammetry (SWCASV) using pencil graphite electrodes (PGE) was developed for the individual and simultaneous determination of the anticancer drugs flutamide (Flu) and irinotecan (Irino) in biological fluids. Calibration curves showed an excellent linear response with limits of detection of 1.68×10^?9 and 1.55×10^?8 M Irino and Flu, respectively. The statistical evaluation of within‐day repeatability (n=5) and day to day precision (n=5) showed satisfactory accuracy and precision. SWCASV using a PGE for individual and simultaneous determination of both drugs in bulk form, human urine and serum samples was demonstrated.     

络合吸附催化不可逆循环叠式方波伏安法

研究了络合吸附催化不可逆体系受前行化学反应控制（Ｋ＜＜１）和不受前行化学反应控制（Ｋ＞＞１）两种情况下的循环叠式方波伏安法的电流理论，并进行了实验验证，讨论了电流特性，获得区分Ｋ＜＜１和Ｋ＞＞１的判据。对于上述体系的测定，循环叠式方波伏安法的灵敏度比普通差式采样方波伏安法高一个数理级以上。     

Sensitive,Accurate and Selective Determination of Cd(II) Using Anodic Stripping Voltammetry with in-situ Hg-Bi Film Modified Pencil Graphite Electrode After Magnetic Dispersive Solid Phase Microextraction

This paper describes a novel approach to detect Cd(II) using the combination of the differential pulse anodic stripping voltammetry and magnetic nanoparticle based dispersive solid phase microextraction as an efficient, green and accurate method. Currents of Cd(II) increased linearly in the range from 75 to 2000 ng L⁻¹ Cd(II) with a detection limit of 21.6 ng L⁻¹. The RSD values of 2.6 and 6.0 % for 1.00 and 0.10 μg L⁻¹ respectively showed that proposed method has an acceptable repeatability. Recovery values between 92.3 and 98.6 % showed that this approach can be successfully used for determination of Cd(II) in water samples.     

The Use of Ultrasound for the Analytical Determination of Nitrite on Diamond Electrodes by Square Wave Voltammetry

Abstract

This work describes an analytical methodology for the determination of nitrite ions in aqueous solutions using boron‐doped diamond electrodes and square wave voltammetry associated with ultrasound radiation. The nitrite ions were oxidized to nitrate ions in Britton‐Robinson buffer solutions 0.1 M, pH 2.0 at 1.0 V versus Ag/AgCl. The voltammetric response of nitrite in the presence of ultrasound showed a peak current five times higher than the obtained in silent conditions. Thus, the detection limit obtained in the presence of radiation was 17 nM (0.782 µg l^?1), a small value if compared with that obtained in the absence of ultrasound: 140 nM (6.44 µg l^?1).     

Pretreated Pencil Graphite Electrode as a Versatile Platform for Easy Measurement of Diclofenac Sodium in a Number of Biological and Pharmaceutical Samples

A pretreated pencil graphite electrode (PPGE) as an electrochemical sensor was developed and applied to measure diclofenac sodium (DIC). The effects of both potentiostatic and potentiodynamic strategies in the electrochemical pretreatment and performance of the electrode were studied, and it was concluded that the former offers better analytical sensitivity for electroanalytical purposes. PPGE displayed good electrocatalytic activity in comparison to nonpretreated PGE (NPGE). Differential pulse voltammetry (DPV) was used to determine DIC. Therefore, a calibration graph was plotted between the variation of anodic peak currents and the DIC concentration, which was found to be linear in the range 0.23–12.95 μmol/L with the detection limit (S/N = 3) of 0.12 μmol/L. PPGE was utilized to determine DIC in real samples such as biological and pharmaceutical ones, and the good recovery values obtained demonstrated the high accuracy of the modified electrode.     

方波伏安法评估聚苯胺膜修饰电极的电荷传输速度

研究导电聚合物的电荷传输机制与速度对于其在应用方面的研究极为重要［‘］．例如在电池的研究中，充放电的速度决定于导电聚合物的电荷传输速度；在电致变色器件的研究中，响应时间也是决定于导电聚合物在氧化还原态间的变化速度，即电荷传输速度．显然较低的电荷传输速度不利于器件的实用化，因此人们必须找到一种能够迅速准确评价电荷传输速度的方法，由于导电聚合物是一个特殊的体系，用一般的电化学方法对其电荷传输速度进行测定时常常遇到这样或那样的问题［‘j．一般说来，导电聚合物的氧化还原过程中均伴随着抗衡离子的运动．体系…     

方波伏安法测定孔雀石绿上染率

采用循环伏安法和方波伏安法研究了阳离子染料孔雀石绿(MG)在H2SO4底液(pH 1.0)中的电化学行为.在0.1 V/s的扫描速率下,MG在碳糊电极上显示一个不可逆氧化峰:0.82 V(Pa,2);一对准可逆氧化还原峰:0.51 V(Pa,1)、0.48 V(Pc)(Ep vs.SCE).在0.05～0.9 V/s的扫速范围内,3个峰的峰电流与扫速的平方根都成正比,表明MG的电氧化还原过程均受扩散控制.计时库仑法测得MG的扩散系数为2.31×10-7cm2/s,表面覆盖度是1.18×10-11mol/cm2.还原峰Pc的峰电流与MG的浓度在8.00×10-6～1.00×10-4 mol/L范围内呈线性关系,检出限为6.6 μmol/L(S/N=3),染色工艺中常用的匀染剂"平平加O"和MG染色体系中常见的无机离子不干扰测定.本方法用于测定MG上染腈纶的上染率,结果与分光光度法一致.     

Nickel and Tungsten Bimetallic Nanoparticles Modified Pencil Graphite Electrode: A High-performance Electrochemical Sensor for Detection of Endocrine Disruptor Bisphenol A

In this work, an economically viable, very low cost, indigenous, ubiquitously available electrochemical sensor based on bimetallic nickel and tungsten nanoparticles modified pencil graphite electrode (NiNP-WNP@PGE) was fabricated for the sensitive and selective detection of bisphenol A (BPA). The NiNP-WNP@PGE sensor was prepared by a facile electrochemical one step co-deposition method. The prepared nanocomposite was morphologically characterized by scanning electron microscopy (SEM), energy dispersive X-ray (EDX), X-ray diffraction (XRD), electrochemically by cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The proposed sensor displayed high electrocatalytic activity towards electro-oxidation of BPA with one irreversible peak. The fabricated sensor displayed a wide detection window between 0.025 μM and 250 μM with a limit of detection of 0.012 μM. PGE sensor was successfully engaged for the detection of BPA in bottled water, biological, and baby glass samples.     

Electroanalytical Determination of Promethazine Hydrochloride in Pharmaceutical Formulations on Highly Boron‐Doped Diamond Electrodes Using Square‐Wave Adsorptive Voltammetry

The electrochemical oxidation of promethazine hydrochloride was made on highly boron‐doped diamond electrodes. Cyclic voltammetry experiments showed that the oxidation mechanisms involved the formation of an adsorbed product that is more readily oxidized, producing a new peak with lower potential values whose intensity can be increased by applying the accumulation potential for given times. The parameters were optimized and the highest current intensities were obtained by applying +0.78 V for 30 seconds. The square‐wave adsorptive voltammetry results obtained in BR buffer showed two well‐defined peaks, dependent on the pH and on the voltammetric parameters. The best responses were obtained at pH 4.0, frequency of 50 s^?1, step of 2 mV, and amplitude of 50 mV. Under these conditions, linear responses were obtained for concentrations from 5.96×10^?7 to 4.76×10^?6 mol L^?1, and calculated detection limits of 2.66×10^?8 mol L^?1 (8.51 μg L^?1) for peak 1 and of 4.61×10^?8 mol L^?1 (14.77 μg L^?1) for peak 2. The precision and accuracy were evaluated by repeatability and reproducibility experiments, which yielded values of less than 5.00% for both voltammetric peaks. The applicability of this procedure was tested on commercial formulations of promethazine hydrochloride by observing the stability, specificity, recovery and precision of the procedure in complex samples. All results obtained were compared to recommended procedure by British Pharmacopeia. The voltammetric results indicate that the proposed procedure is stable and sensitive, with good reproducibility even when the accumulation steps involve short times. It is therefore very suitable for the development of the electroanalytical procedure, providing adequate sensitivity and a reliable method.     

Enhanced Specificity and Sensitivity for the Determination of Nickel(II) by Square-wave Adsorptive Cathodic Stripping Voltammetry at Disposable Graphene-modified Pencil Graphite Electrodes

Chemical sensors relying on graphene-based materials have been widely used for electrochemical determination of metal ions and have demonstrated excellent signal amplification. This study reports an electrochemically reduced graphene oxide (ERGO)/mercury film (HgF) nanocomposite-modified pencil graphite electrode (PGE) prepared through successive electrochemical reduction of graphene oxide (GO) sheets and an in situ plated HgF. The ERGO-PG-HgFE, in combination with dimethylglyoxime (DMG) and square-wave adsorptive cathodic stripping voltammetry (SW-AdCSV), was evaluated for the determination of Ni²⁺ in tap and natural river water samples. A single-step electrode pre-concentration approach was employed for the in situ Hg-film electroplating, metal-chelate complex formation, and non-electrolytic adsorption at –0.7 V. The current response due to nickel-dimethylglyoxime [Ni(II)-DMG₂] complex reduction was studied as a function of experimental paratmeters including the accumulation potential, accumulation time, rotation speed, frequency and amplitude, and carefully optimized for the determination of Ni²⁺ at low concentration levels (μg?L^?1) in pH 9.4 of 0.1 M NH₃–NH₄Cl buffer. The reduction peak currents were linear with the Ni²⁺ concentration between 2 and 16?μg?L^?1. The limits of detection and quantitation were 0.120?±?0.002?µg?L^?1 and 0.401?±?0.007?µg?L^?1 respectively, for the determination of Ni²⁺ at an accumulation time of 120?s. The ERGO-PG-HgFE further demonstrated a highly selective stripping response toward Ni²⁺ determination compared to Co²⁺. The electrode was found to be sufficiently sensitive to determine metal ions in water samples at 0.1?µg?L^?1, well below the World Health Organization standards.     

Low Cost Hydrogen Peroxide Sensor from Manganese Oxides Modified Pencil Graphite Electrode

Electrodeposition of manganese oxides film onto the cheap pencil graphite electrode using potassium permanganate precursor provides the good alternative method of fabrication the low cost hydrogen peroxide sensor. Effect of deposition potential, deposition time and concentration of potassium permanganate were investigated. The modified electrode displayed electrocatalytic activity towards the oxidation of hydrogen peroxide in alkaline medium. Amperometric detection of hydrogen peroxide in ammonium buffer pH 9.0 is possible at the operation potential of +0.50V vs Ag/AgCl instead of over +0.80V vs Ag/AgCl with unmodified electrode. Linear concentration range between 0.50-138ppm of hydrogen peroxide was obtained with a detection limit of 0.28ppm.     

Determination of Cysteine at Bismuth Nanostructure – Carbon Ionic Liquid Electrode by Square Wave Voltammetry

Bismuth nanostructure‐carbon ionic liquid electrode has been employed for sensitive determination of cysteine (Cys). Bismuth nanostructure was incorporated into the carbon ionic liquid electrode (CILE) and applied for determination of cysteine. An interaction was taking place between bismuth nanostructure and the thiol group of cysteine. The bismuth cysteinate complex oxidation potential occurred at more negative potential compared to the cysteine oxidation peak obtained at bare carbon ionic liquid electrode (CILE). Square wave voltammetry (SWV) was used for the determination of the cysteine and satisfactory results were obtained. The calibration curve was linear in the concentration range of 1 to 500 µM and 0.5–2 mM of Cys. A low detection limit of 0.5 µM was achieved for Cys. The electrode showed a good selectivity for determination of cysteine in the presence of other amino acids. The proposed electrode was satisfactory applied for the determination of cysteine in human serum plasma sample.     

氧化锌修饰铅笔芯电极电致化学发光法测定苯酚的研究

采用滴涂法将氧化锌纳米颗粒滴涂在自制铅笔芯电极上制成氧化锌修饰铅笔芯电极,当以过硫酸根为共反应剂时,该修饰电极在氢氧化钠溶液中具有良好的电致化学发光(ECL)行为,对其发光机理进行了考察。基于苯酚对该修饰电极的ECL具有抑制作用,建立了一种测量苯酚的新方法,当苯酚浓度为2×10~(-8)~2×10~(-6)mol/L时,发光强度与苯酚浓度的对数呈线性关系,检出限为1×10~(-8)mol/L。该方法具有灵敏度高、方法简单、快速、稳定性好等优点,将其应用于工业废水中苯酚浓度的检测,回收率为96.5%~104.5%。     

Sensitive Flow-Injection Electrochemical Determination of Hydrogen Peroxide at a Palladium Nanoparticle-Modified Pencil Graphite Electrode

A novel flow-injection amperometric method was proposed for the sensitive and enzymeless determination of hydrogen peroxide based on its electrocatalytic reduction at a palladium nanoparticle-modified pretreated pencil graphite electrode in a laboratory-constructed electrochemical flow cell. Cyclic voltammograms of the unmodified and modified electrodes were recorded in pH 7.0 phosphate buffer containing 0.10 M KCl at a scan rate of 50?mV s^?1 for the investigation of electrocatalytic reduction of hydrogen peroxide at the palladium nanoparticle-modified pretreated pencil graphite electrode. Cyclic voltammograms of the pretreated pencil graphite electrode revealed an irreversible oxidation peak and a weak reduction peak of hydrogen peroxide at +1100?mV and –450?mV vs. an Ag/AgCl/KCl saturated reference electrode. However, the reduction of hydrogen peroxide was observed at –100?mV with an increase in current in the cyclic voltammograms of the palladium nanoparticle-modified pretreated pencil graphite electrode compared to the unmodified electrode. These results indicate that the palladium nanoparticle-modified pretreated pencil graphite electrode exhibits efficient electrocatalytic activity for the reduction of hydrogen peroxide. A linear concentration range was obtained between .01 and 10.0?mM hydrogen peroxide with a detection limit of 3.0 µM from flow injection amperometric current–time curves recorded in pH 7.0 phosphate buffer at –100?mV and a 2.0?mL min^?1 flow rate. The novelty of this work relies on its use of a laboratory-constructed flow cell constructed for the pencil graphite electrode using these inexpensive, disposable, and electrochemically reactive modified electrodes for the amperometric determination of hydrogen peroxide in a flow injection analysis system.