Selective and Sensitive Voltammetric Determination of Dopamine in Blood by Electrochemically Treated Pencil Graphite Electrodes

Preparation of electrochemically treated pencil graphite (ETPG) electrode and its application for the determination of DA in the presence of ascorbic (AA) and uric (UA) acids were investigated. Several important parameters were worked to control the performance of the ETPG electrode which showed a high selectivity and sensitivity toward DA. A linear relationship was obtained for dopamine (DA) over the concentration range of 0.01 and 5.0 μM with a detection limit of 0.31 nM in the presence of AA and UA. The fabrication reproducibility of the ETPG electrodes (n=10) showed an acceptable reproducibility with a RSD of 2.0% for 5.0 μM DA. The determination of DA in blood serum without any pretreatment and dilution has been reported for the first time in this work.     

Voltammetric Determination of Favipiravir Used as an Antiviral Drug for the Treatment of Covid-19 at Pencil Graphite Electrode

This work describes the sensitive voltammetric determination of favipiravir (FAV) based on its reduction for the first time with a low-cost and disposable pencil graphite electrode (PGE). In addition, the determination of FAV was also performed based on its oxidation. Differential pulse (DP) voltammograms recorded in 0.5 M H₂SO₄ for the reduction of FAV show that peak currents increase linearly in the range of 1.0 to 600.0 μM with a limit of detection of 0.35 μM. The acceptable recovery values (98.9–106.0 %) obtained from a pharmaceutical tablet, real human urine, and artificial blood serum samples spiked with FAV confirm the high accuracy of the proposed method.     

A Comparison of Edge-plane and Basal-plane Pyrolytic Graphite Electrodes towards Sensitive Determination of the Fungicide Mandipropamid

A sensitive square-wave voltammetry (SWV) method based on basal-plane pyrolytic graphite electrode (BPPGE) and edge-plane pyrolytic graphite electrode (EPPGE) was developed to determine the concentration of the pesticide mandipropamid (MAN) in spiked river water and grape juice samples. Under optimal experimental conditions, the SWV response of EPPGE and BPPGE was linear over the concentration ranges of 0.7 to 9.0 μmol L⁻¹ and 0.5 to 10.0 μmol L⁻¹, respectively. The method was successfully used to determine MAN in spiked samples with good recovery. Cyclic voltammetry (CV) was conducted to understand the mechanism underlying the electrode process of MAN.     

Electrochemically Treated Pencil Graphite Electrodes Prepared in One Step for the Electrochemical Determination of Paracetamol

This article reports the electrochemical determination of paracetamol (PC) in the presence of ascorbic acid (AA) and caffeine (CF) using an electrochemically treated pencil graphite electrode. In this study, we describe the use of an electrode prepared by overoxidation between 0.0 and +2.1 V for paracetamol determination. The electrochemically treated pencil graphite electrodes (ETPGEs) were prepared using a cyclic voltammetric method. The electrode was characterized by Scanning Electron Microscopy (SEM), Electrochemical Impedance Spectroscopy (EIS), and Resonance Raman Spectroscopy. The differences in oxidation peak potentials were large enough to determine PC in the presence of AA and CF. The electroactive areas of the bare electrode and 10 scan-ETPGE in 0.5 M H₂SO₄ were calculated to be 0.0031 and 0.0341 cm², respectively. The sensor (10 scan-ETPGE in 0.5 M H₂SO₄) was sensitive to the PC with 1.74 × 10^–7 M limits of detection (S/N = 3). Finally, the developed method and the prepared electrodes were used for determination of PC in the pharmaceutical samples.

     

Novel Electrochemically Treated Graphite Pencil Electrode Surfaces for the Determination of Trace α‐Naphthol in Water Samples

An electrochemically treated graphite pencil electrode (PGPE) has been simply prepared for trace level determination of α‐naphthol. The pretreatment of GPE surfaces is conducted in 0.8 M NaOH by cycling the potential between +1.3 and +1.9 V for 50 CV segments at a scan rate of 100 mV s^?1. The influence of the pretreatment is studied extensively, and optimum conditions are obtained. Linear sweep anodic stripping voltammetry (LSASV) is used for the determination of α‐naphthol. Based on the constructed calibration curve, a linear range of 0.01 μM to 2.0 μM with a detection limit of 1.5 nM (S/N=3) is obtained. The results reveal that the electrochemical treatment of the GPE surface improves its electrochemical catalytic activity with reference to surfaces of the non‐treated GPE. The present method is applied for the determination of trace α‐naphthol in real water samples.     

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.     

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.     

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.     

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.     

Titanium Dioxide/Multi-walled Carbon Nanotubes Composite Modified Pencil Graphite Sensor for Sensitive Voltammetric Determination of Propranolol in Real Samples

A very effective electrochemical sensor for the analysis of propranolol was constructed using TiO₂/MWCNT film deposited on the pencil graphite electrode as modifier. The modified electrode represented excellent electrochemical properties such as fast response, high sensitivity and low detection limit. The proposed sensor showed an excellent selective response to propranolol in the presence of foreign species and other drugs. The electrochemical features of the modified electrode were investigated by cyclic voltammetry and electrochemical impedance spectroscopy (EIS) technique which indicated a decrease in resistance of the modified electrode versus bare PGE and MWCNT/PGE. The surface morphology for the modified electrode was determined by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and Fourier transform infrared spectroscopy (FT-IR). Differential pulse technique (DPV) was used to determine propranolol which showed a good analytical response in the linear range of 8.5×10⁻⁸-6.5×10⁻⁶ M with a limit of detection 2.1×10⁻⁸ M. The TiO₂/MWCNT/PGE sensor was conveniently applied for the measurement of propranolol in biological and pharmaceutical media.     

Simple and Sensitive Electrochemiluminescence Method for Determination of Bisphenol a Based on its Inhibitory Effect on the Electrochemiluminescence of Luminol

An electrochemiluminescence inhibition method has been developed for the determination of bisphenol A based on studying the inhibition phenomena of bisphenol A to the electrochemiluminescence of luminol. There is a linear relationship between the inhibitive intensity of electrochemiluminescence and the concentration of bisphenol A in the range of 4.4 × 10^?7 to 2.2 × 10^?5 mol/l. The method was successfully applied to the determination of bisphenol A in hot water in contact with commercially available table‐water bottle samples.     

双分子印迹聚合物微球选择固相萃取环境和食品样品中壬基酚和双酚A

以壬基酚(NP)、双酚A(BPA)为模板分子,a-甲基丙烯酸(MAA)为功能单体,通过乳液聚合法制备了双模板分子印迹聚合物(D-MIP),并以D-MIP为固相萃取填料,建立了双分子印迹固相萃取-高效液相色谱荧光检测环境食品中痕量NP和BPA的方法。采用红外光谱和吸附实验对其性能进行了研究。结果表明,D-MIP对NP和BPA的饱和吸附量分别为73.3和97.5 mg/g,相对选择性系数分别为2.2和1.7。在最佳条件下,本方法的线性范围为0.01~2.3 mg/L(R2>0.998),检出限(S/N=3)为0.001~0.002 mg/L。将本方法应用于江水、啤酒、鲫鱼中NP和BPA含量测定,回收率在86.4%~99.1%范围内,相对标准偏差小于6.2%。本方法选择性好、灵敏度高,对环境和食品中NP和BPA的富集、分离显示出良好的应用前景。     

双酚A分子印迹聚合物的制备和识别性能研究

生物分子间的特异性亲和识别作用在分析化学领域中已得到广泛应用, 但由于这些生物分子获得的途径复杂, 不易保存和使用条件苛刻等局限性而引发人工合成这样一类具有特异性识别和保留性能的吸附材料, 即所谓的分子印迹聚合物(简称为MIP)[1～4]. 双酚A是一种重要的环境内分泌干扰物, 它能与人体的内源雌激素雌二醇竞争结合雌激素受体, 并可能引起一系列病变[5,6]. 本文选择4-乙烯基吡啶作为功能单体, 加入交联剂乙二醇二甲基丙烯酸酯和引发剂偶氮二异丁腈引发聚合, 分别制备了以双酚A为模板分子的分子印迹聚合物和相应的空白聚合物. 研究了几种酚类结构类似物在所得分子印迹柱上的保留特性, 对双酚A分子印迹聚合物用作固相萃取剂的性能进行了初步研究.     

羧基化单壁碳纳米管涂层同时测定纯净水中的烷基酚和双酚A

用溶胶-凝胶方法制备了羧基化碳纳米管溶胶凝胶固相微萃取涂层,采用顶空固相微萃取-气相色谱法测定纯净水中的烷基酚和双酚A.优化了萃取涂层的萃取时间、萃取温度、盐浓度以及解析时间等实验参数.结果表明,在萃取温度为90℃和盐浓度为0.36 g/mL的条件下萃取30 min,250℃下解析3 min,涂层的萃取效果最好.与商用...     

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.     

FeS2 Grown Pencil Graphite as an In‐expensive and Non‐enzymatic Sensor for Sensitive Detection of Uric Acid in Non‐invasive Samples

While most electrochemical uric acid (UA) sensors are developed on the conventional electrodes and involve either multiple steps based synthesis routes and/or complicated fabrication processes, this paper is the first demonstration of direct growth of pyrite FeS₂ on pencil‐graphite electrode (PGE) for non‐enzymatic UA sensing. FESEM images of the pyrite FeS₂‐PGE reveal mesoporous microspherical structure of pyrite FeS₂ along with graphite flakes of PGE and EDX, Raman spectroscopic data validate growing of pyrite FeS₂ on PGE. The pyrite FeS₂‐PGE sensor exhibited detection limit of 6.7 μM, excellent linearity, reproducibility, selectivity over glucose, urea, ascorbic acid with the sensitivity of 370 μA mM^?1 cm^?2 in the range of 10–725 μM of UA. These improved analytical performances can be attributed to high conductivity of the pyrite FeS₂, larger electro‐active surface area of the mesoporous microspherical pyrite FeS₂ grown on PGE (than only PGE) and abundance in defect sites originating from both the pyrite FeS₂ as well as functional groups of pencil graphite. Furthermore, the sensor was validated against UA in urine sample and the result supports well with the UA concentration achieved from colorimetric technique. Development of this low cost, non‐enzymatic, sensitive and highly selective pyrite FeS₂‐PGE bases UA sensor is a significant step in the development of practically viable sensors for point‐of‐care applications in clinical and pharmaceutical analyses.     

A Facile and Cost‐effective Electroanalytical Strategy for the Quantification of Deoxyguanosine and Deoxyadenosine in Oligonucleotides Using Screen‐printed Graphite Electrodes

The development of electroanalytical methods for the detection and quantification of nucleotides in DNA offers vital implications in assessing the degree of oxidation or epigenetic modification in DNA. Unfortunately, the electrochemical response of oligonucleotides is strongly influenced by the size, composition and nucleic base sequence. In this article, an optimized analytical procedure for the enzymatically breakdown of the oligonucleotides to their corresponding nucleotides for the evaluation of the electrochemical response through the use of square wave voltammetry (SWV) is presented. Enzymatic digestion of oligonucleotides has been optimized in terms of buffer composition, digestion time, strategy for stopping the enzymatic reaction and filtration requirement for enzyme removal, and then compared to an established protocol. Under the optimized protocol SWV response of a number of untreated and enzymatically digested six‐mer oligonucleotides, namely 5′‐GGGGGG‐3′, 5′‐AAAAAA‐3′, 5′‐CGCGCG‐3′ and 5′‐AAACGC‐3′ have been analysed, providing a higher sensitivity for the determination of guanosine and adenosine monophosphate species under digestion conditions with a more facile and cost effective procedure. The novel strategy for the enzymatically treated oligonucleotides in combination with the SWV response provides a proof of principle for feasible applications in the diagnosis of methylated guanosine in DNA as a potential biomarker due to its relation with cancer.     

POMs as Active Center for Sensitively Electrochemical Detection of Bisphenol A and Acetaminophen

A new type of electrochemical sensor based on multi-walled carbon nanotubes(MWCNTs), K2H4SiW11CuO39-6H2O(SiW11Cu) and gold nanoparticles(AuNPs) was prepared for the simultaneous detection of bisphenol A and acetaminophen. Differential pulse voltammetry(DPV), cyclic voltammetry(CV) and electrochemical impedance spectroscopy(EIS) were used for electrochemical characterization, and Fourier transfonn infrared spectroscopy(FTIR) was used to characterize the structure of polyoxometalates. Electrochemical experimental results show that the composite modified electrodes have good electrochemical activity as well as current response values of bisphenol A and acetaminophen when pH=7.0. At the same time, the modified electrode exhibits good stability and reproduction, and has good anti-interference ability to other substances. In practical application, the sensor obtained satisfactory results.     

溶剂浮选-高效液相色谱法测定水体中双酚A、辛基酚和壬基酚

以正辛醇为溶剂对水样中双酚A、辛基酚和壬基酚进行溶剂浮选分离和富集。水样溶液的适宜酸度为pH3,通入速率为60mL·min-1氮气浮选90min。浮选完成时,分取上层清液10μL供高效液相色谱分析用。上述3种环境激素的检出限(3s/b)依次为0.025,0.011,0.042μg.L-1。以不含上述化合物的水样作为基体,采用标准加入法对方法做回收试验,测得回收率在93.3%～102.0%之间,测定值的相对标准偏差(n=7)在1.3%～4.9%之间。     

A Novel Sensitive and Selective Amperometric Detection Platform for the Vanillin Content in Real Samples

Accurate and sensitive determination of vanillin in commercial samples is significant for food safety & quality. In the proposed study, copper particles were coated on an indium tin oxide electrode (ITO) by cyclic voltammetry (CV) for the determination of vanillin in food samples. CV studies indicated that the electrodeposition of Cu particles provides a good electrocatalytic effect towards the oxidation of vanillin. The fabricated sensor determines vanillin linearly between 0.50 μM–2.0 mM (Limit of detection: 0.15 μM). The Cu/ITO was successfully tested on vanillin samples and the recommended method provides accurate and selective determination of vanillin in daily samples.