Sensitive Electrochemical Determination of Trifluralin at a Disposable Pencil Graphite Electrode

A sensitive differential pulse (DP) voltammetric method has been proposed for the determination of trifluralin (TFA) based on both its reduction and oxidation at a disposable pencil graphite electrode (PGE). DP voltammograms recorded under optimized conditions show that oxidation and reduction peak currents increased linearly in the range from 1.0 to 75.0 μM and from 0.50 to 100.0 μM TFA, respectively. LOD and sensitivity values have been determined as 0.39 μM and 11170 μA mM⁻¹ cm⁻² for oxidation and as 0.20 μM and 22167 μA mM⁻¹ cm⁻² for reduction. The acceptable recovery values (95.2–104.8 %) were obtained from real water samples.     

Voltammetric Determination of Oxybutynin Hydrochloride Utilizing Pencil Graphite Electrode Decorated with Gold Nanoparticles

A novel voltammetric method was successfully applied for the determination of an anticholinergic drug, oxybutynin hydrochloride (OXB). The method is concerned with electrooxidation of the drug on the surface of pencil graphite electrode (PGE). In order to enhance the electrode sensitivity and peak current, the electrode was coated with gold nanoparticles (Au-NPs) via electrochemical deposition using cyclic voltammetry from gold salt solution. The surface of Au-NPs modified PGE has been characterized using scanning electron microscopy and X-ray photoelectron spectroscopy. Various experimental variables were studied and optimized to enhance the sensor's response towards OXB. Quantitative determination of the drug was achieved in phosphate buffer pH 7.5 using differential pulse voltammetry by scanning the potential over range of 0.00 to 2.20 V with scan rate of 40 mV s⁻¹. Validation of the method was achieved according to ICH guidelines. The method was found to be linear over concentration range (2.0×10⁻⁷–1.0×10⁻⁶ M). The suggested sensor was efficiently developed for the quantitative determination of OXB in pure form, pharmaceutical dosage form and spiked plasma samples.     

Voltammetric Determination of Hemoglobin Using a Pencil Lead Electrode

In this paper the electrochemical behavior of hemoglobin (Hb) immobilized on a pencil lead electrode (PLE) was investigated. Immobilization of Hb on the pencil lead electrode was performed by nonelectrochemical and electrochemical methods. In phosphate buffer solution with pH 7.0 Hb showed a pair of well‐defined and nearly reversible redox waves (the anodic and cathodic peak potentials are located at ?0.18 V and ?0.22 V, respectively). The dependence of the anodic peak potential (E_pa) on the pH of the buffer solution indicated that the conversion of Hb? Fe(III)/Hb? Fe(II) is a one‐electron‐transfer reaction process coupled with one‐proton‐transfer. In addition the effect of scan rate on peak currents and peak separation potential was investigated and electrochemical parameters such as α and k_s were calculated. In the second part of this work, the ability of the electrode for determination of Hb concentration was investigated. The results showed a linear dynamic range from 0.15 to 2 µM and a detection limit of 0.11 µM. The relative standard deviation is 4.1 % for 4 successive determinations of a 1 µM Hb solution.     

蜡浸石墨碳电极伏安法测定维生素B6的研究

本文以表面直径3mm的蜡浸石墨碳为工作电极,在0.3mol/L NH_3·H_2O-NH_4Cl基底溶液中,用单扫描示波极谱仪制作VB_6的阳极化二阶导数极谱曲线,其峰电位Ep为+0.65V(vs SCE)。在1～70μg/ml范围内,峰幅高ip与浓度间呈线性关系。方法应用于药剂分析中,误差在±5％以内。     

Voltammetric Study of Aminopurines on Pencil Graphite Electrode in the Presence of Copper Ions

Electrochemical oxidations of aminopurines (adenine, 2‐aminopurine, 2,6‐diaminopurine) and their complexes with Cu(I) on a pencil graphite electrode were investigated by means of linear sweep voltammetry (LSV) and elimination voltammetry with linear scan (EVLS). The anodic process of the Cu(I)‐aminopurine complex, corresponding to the oxidation of Cu(I) to Cu(II), takes place in the potential range between 0.4 and 0.5 V (vs. Ag/AgCl/3 M KCl). At more positive potentials the aminopurines provide voltammetric peaks resulting from the oxidation of the purine ring. The stability of the accumulated complex layer was investigated by the adsorptive transfer stripping technique.     

Voltammetric Determination of an Anti-rheumatoid Drug Acemetacin on Graphite Flake Paste Electrode and Glassy Carbon Electrode

In this study, a simple and sensitive square wave voltammetric procedure has been developed for the determination of acemetacin (ACM) at graphite flake paste electrode (GFPE) and glassy carbon electrode (GCE). Under optimized conditions, the dependence of ACM peak current on its concentration showed wide linear range: 0.03–1.0 μmol L⁻¹ and 0.7–15.0 μmol L⁻¹ at GFPE and GCE, respectively. The developed method was successfully applied for the determination of ACM in pharmaceuticals and spiked urine with satisfying recoveries. The electrochemical oxidation of ACM is an irreversible process controlled by mixed nature of the mass transfer process.     

A Pencil Graphite Electrode In Situ Modified by Monovalent Copper: a Promising Tool for the Determination of Methylxanthines

A pencil graphite electrode (PeGE) exhibits a promising tool for the electrochemical analysis of xanthine (Xan) and its N‐methyl derivatives (1‐, 3‐, 7‐ and 9‐mXan). The changes in their level in blood, serum, urine, as products of purine catabolism, can indicate the development of some diseases. Sensitivity‐enhanced voltammetric detection of mXans was achieved by forming of complex with Cu(I) and application of elimination procedure. The Cu(I)‐mXan complex was identified by means of titration of electrochemically produced cuprous ions by mXan. Our approach enables separation of overlapped mXan oxidation signals. Based on the obtained results, we found that the effect of methyl group position on the xanthine skeleton was significant and it was also discussed.     

Development of a Diamond Nanoparticles-based Nanosensor for Detection and Determination of Antiviral Drug Favipiravir

This study developed a nanosensor for the detection and determination of favipiravir, a presumed drug that has potential therapeutic efficacy in treating COVID-19 patients, from tablets and serum samples. This nanosensor was obtained by adding the optimum amount of diamond nanoparticles into carbon paste. For the determination of favipiravir adsorptive stripping differential pulse (AdSDPV) and adsorptive stripping square wave voltammetry (AdSSWV) were used. Limit of detection values were found as 4.83×10⁻⁹ M and 2.44×10⁻⁷ M for bulk and 5.18×10⁻⁸ M and 4.38×10⁻⁸ M for serum samples using AdSDPV and AdSSWV, respectively. Recovery studies made of the tablet and serum produced satisfactory results.     

铅笔芯电极作为工作电极-导数伏安法测定核黄素

用1B铅笔芯制成聚甲基丙烯酸甲酯包裹的铅笔芯电极。将此电极置于pH 2.20磷酸盐缓冲溶液中,在-1.5~+2.0V(vs.SCE)电位区间,以0.1V·s-1扫描速率连续扫描30圈使其活化。试验表明:在pH 4.8的乙酸盐底液中,核黄素在此电极上产生还原峰,其峰电位在-0.300V(vs.SCE)。其峰电流的导数与核黄素的质量浓度在1.88×10-4~0.376mg·L-1范围内呈线性关系,其检出限(3S/N)为4.42×10-5 mg·L-1,应用此方法测定了维生素B2片剂中核黄素的含量,所得测定值与其标示值相符。在此样品的基础上做加标回收试验,测得回收率在96.5%~111%之间,测定值的相对标准偏差(n=5)为2.5%。     

Pencil Lead Electrode Modified with Hemoglobin Film as a Novel Biosensor for Nitrite Determination

In the present paper, the electrochemical reduction of nitrite at a hemoglobin modified pencil lead electrode (Hb/PLE) is described. The electrochemical properties of nitrite were studied by cyclic voltammetry and chronoamperometry. Results showed that the hemoglobin film has an excellent electrochemical activity towards the reduction of nitrite. By using voltammetric and chronoamperometric methods, α, n_α and n were calculated. Then the ability of the electrode for nitrite determination was investigated using differential pulse voltammetry. The electrocatalytic reduction peak currents were found to be linear with the nitrite concentration in the range from 10 to 220 µM with a detection limit of 5 µM. The relative standard deviation is 2 % for 3 successive determinations of a 100 µM nitrite solution. This modified electrode was successfully used for the detection of low amounts of NO₂^? in spinach sample and a spiked sample of tap water.     

Voltammetric Determination of Folic Acid Using a Graphite Paste Electrode

A simple differential pulse voltammetric method based on a graphite paste electrode (GPE) was developed for the quantitative determination of folic acid (FA) in tablets. The electrode exhibits a clear improvement of the current response. A linear response in the electroanalytical approach exists from 4.97×10^?6 to 2.94×10^?5 mol L^?1 with a limit of detection of about 2.67×10^?6 mol L^?1 in KCl solutions. The developed procedure was tested by recovery studies and compared with spectrophotometric and chromatographic methods. The results are described and discussed in the light of existing literature.     

Flow Injection Amperometric Analysis of H2O2 at Platinum Nanoparticles Modified Pencil Graphite Electrode

A Pt nanoparticle modified Pencil Graphite Electrode (PGE) was proposed for the electrocatalytic oxidation and non‐enzymatic determination of H₂O₂ in Flow Injection Analysis (FIA) system. Platinum nanoparticles (PtNPs) electrochemically deposited on pretreated PGE (p.PGE) surface by recording cyclic voltammograms of 1.0 mM of H₂PtCl₆ solution in 0.10 M KCl at scan rate of 50 mV s⁻¹ for 30 cycles. Cyclic voltammograms show that the oxidation peak potential of H₂O₂ shifts from about +700 mV at bare PGE to +50 mV at PtNPs/p.PGE vs. Ag/AgCl /KCl (sat.). It can be concluded that PtNPs/p.PGE exhibits a good electrocatalytic activity towards oxidation of H₂O₂. Then, FI amperometric analysis of H₂O₂ was performed under optimized conditions using a new homemade electrochemical flow cell which was constructed for PGE. Linear range was found as 2.5 μM to 750.0 μM H₂O₂ with a detection limit of 0.73 μM (based on S_b/m of 3). As a result, this study shows the first study on the FI amperometric determination of H₂O₂ at PtNPs/p.PGE which exhibits a simple, low cost, commercially available, disposable sensor for H₂O₂ detection. The proposed electrode was successfully applied to determination of H₂O₂ in real sample.     

浸蜡石墨电极伏安法测定抗癌药物盐酸阿霉素

本用自制浸蜡光谱纯石墨电极伏安法测定盐酸阿霉素。在ＰＨ＝６．０的磷酸缓冲溶液体系中，盐酸阿霉素在５．０×１０＾－８ｍｏｌ／Ｌ－１．０×１０＾－６ｍｏｌ／Ｌ范围内浓度与电流呈线性检测限可达１．０×１０＾－８ｍｏｌ／Ｌ。方法选择性好，抗干扰能力强，不需样品分离可直接进行测定。结果令人满意。     

Development of Simple Electrochemical Sensor for Selective Determination of Methadone in Biological Samples Using Multi‐walled Carbon Nanotubes Modified Pencil Graphite Electrode

The electrochemical sensor was developed for determination of methadone (MTD) using multi‐walled carbon nanotubes (MWCNT) modified pencil graphite electrode (MWCNT‐PGE). It was found that the oxidation peak current of MTD at the MWCNT‐PGE was greatly improved compared with that of the bare‐PGE. At the MWCNT‐PGE, well‐defined anodic peak of MTD was observed at about 0.7 V (in pH 7 solution). The influence of several parameters on the determination of MTD was investigated. At optimum experimental conditions, differential pulse voltammetry (DPV) was used for determination of MTD, which exhibited a linear calibration graph of Ip versus MTD concentration in the range of 0.1–15 µM with a correlation coefficient of 0.9992. The calculated detection limit for S/N = 3 was 87 nM. It has been shown that the peaks obtained for oxidation of ascorbic acid (AA), uric acid (UA) and MTD in their mixture could be well resolved by differential pulse voltammetry, permitting us to develop a sensitive and selective electrochemical sensor for determination of MTD in the presence of AA and UA. Finally, MWCNT‐PGE was used for determination of MTD in biological samples, such as human serum and urine, using the standard addition procedure and the results were quite promising.     

Single-Sweep Voltammetric Determination of Tamoxifen at Carbon Paste Electrode

Abstract

A single-sweep voltammetric method was proposed for the determination of tamoxifen. The proposed method took advantage of both the accumulation of carbon paste electrode toward tamoxifen and the rapidity of single-sweep voltammetry. In HAc-NaAc (pH 4.1) buffer/methanol (85:15 v/v) mixed solution, an irreversible oxidation peak of tamoxifen was observed at 1.1 V (versus SCE). The second-order derivative peak current of tamoxifen and its concentration plots were rectilinear over the range of 7.0 × 10^?10 ～ 3.0 × 10^?8 mol · l^?1 with a detection limit of 1.0 × 10^?10 mol · l^?1 without any preconcentration. The proposed method was evaluated by analyzing tamoxifen citrate tablets, which was characterized by rapidity and higher sensitivity.     

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.     

Voltammetry of Benzo[a]pyrene in Aqueous and Nonaqueous Media: Adsorptive Stripping Voltammetric Determination at Pencil Graphite Electrode

A detailed study of the electrochemical oxidation of Benzo[a]pyrene (BaP) at the glassy carbon and pencil graphite electrodes was carried out in aqueous and nonaqueous media. Using square‐wave stripping mode, the compound yielded a well‐defined voltammetric response at pencil graphite electrode in acetate buffer, pH 4.8 at +1.13 V (vs. Ag/AgCl) (a preconcentration step being carried out at a fixed potential of +0.70 V for 180 s). The process could be used to determine BaP concentrations in the range 0.25–1.25 μM, with a detection limit of 0.027 μM (6.82 μg L^?1). The applicability to assay of spiked human urine samples was also illustrated.     

Cathodized Gold Nanoparticle‐Modified Graphite Pencil Electrode for Non‐Enzymatic Sensitive Voltammetric Detection of Glucose

A highly sensitive enzymeless electrochemical glucose sensor has been developed based on the simply prepared cathodized gold nanoparticle‐modified graphite pencil electrode (AuNP‐GPE). Cyclic voltammetry (CV) experiments show that AuNP‐GPE is able to oxidize glucose partially at low potential (around −0.27) whereas the bare GPE cannot oxidize glucose in the entire tested potential windows. Besides, fructose and sucrose cannot be oxidized at potential lower than +0.1 V at AuNP‐GPE. As a result, the glucose oxidation peak at around −0.27 V is suitable enough for selective detection of glucose in the presence of fructose and sucrose. Cathodization of AuNP‐GPE under optimum condition (‐1.0 V for 30 s) in the same glucose solution before voltammetric measurement enhanced glucose oxidation peak current around −0.27 V to achieve an efficient electrochemical sensor for glucose with a detection limit of 12 μM and dynamic range between 0.05 to 5.0 mM with a good linearity (R²= 0.999). Almost no interference effect was observed for sensing of glucose in the presence of ascorbic acid, alanine, phenylalanine, fructose, sucrose, and NaCl.     

Disposable Pencil Graphite Electrode for Ciprofloxacin Determination in Pharmaceutical Formulations by Square Wave Voltammetry

In this work, a new electrochemical sensor based on pencil graphite with interesting features, such as low cost (US$ 0.01 per electrode), ease manufacture, and portability was developed. The sensor showed an adequate manufacturing reproducibility with RSD <5.3 %. Under this electrochemical platform, ciprofloxacin underwent an irreversible oxidation process at 1.03 V, characterized by the diffusion of electroactive species. A simple method by square wave voltammetry (SWV) has been optimized for the determination of ciprofloxacin in pharmaceutical formulations using a pencil graphite electrode (PGE). The method showed satisfactory analytical performance, with a wide linear range (12 to 55 μmol L⁻¹), low detection limit (5.6 μmol L⁻¹), adequate precision (RSD <3.2 %), and accuracy with an average recovery of (102±15)%. Samples of pharmaceutical formulations were evaluated, obtaining levels of ciprofloxacin close to those established by the manufacturers. In addition, the samples were analyzed by liquid chromatography and there was no significant difference between the methods at the 95 % confidence level. In this sense, the method developed proved to be reliable and promising for the quality control of pharmaceutical formulations.     

Electrochemical Determination of Homocysteine at Disposable Graphite Electrodes

In the case of disruption of Hcy metabolism, the blood level of Hcy increases and it causes particularly the cardiovascular diseases, cancer, dementia and Parkinson’s disease. Thus, the sensitive analysis of Hcy levels in biological fluids is very important. Hcy analysis was performed herein using very practical and cost‐effective protocol using differential pulse voltammetry and graphite electrode. Detection limit of Hcy was found to be 1.21 µM in the linear range from 2 µM to 20 µM. The electrochemical Hcy detection in artificial urine medium was also successfully performed even in the presence of L ‐Cysteine, L ‐Methionine and Glutathione.