An electrochemical sensor based on TiO2/activated carbon nanocomposite modified screen printed electrode and its performance for phenolic compounds detection in water samples

Herein, we reported a titanium oxide (TiO₂) modified activated carbon nanocomposite that showed advantageous characteristics in terms of electro-conductivity, catalytic activity and surface area. The designed nanocomposite was employed to modify the screen printed carbon electrode transducer surface in the construction of an electrochemical sensor. The electrode surface modification was characterised by cyclic voltammetry and impedimetric studies. The modified transducer surface was subsequently used for the detection of four phenolic endocrine disruptors, p-nitrophenol, hydroquinone, catechol and 1-naphtol. Under optimal conditions, TiO₂ modified activated carbon sensor was evaluated by differential pulse voltammetry showing a good linearity with correlation coefficients higher than 0.99. It showed, in parallel, a high sensitivity where the detection limits were 348 ng/L, 110.1 ng/L, 3.3 ng/L and 7.2 µg/L for the respective studied compounds (S/N = 3). Finally, we validated the method with river water samples, and good recovery values were obtained showing the potential application of the reported biosensor.     

Enhanced Sensing of Carbendazim,a Fungicide on Functionalized Multiwalled Carbon Nanotube Modified Glassy Carbon Electrode and Its Determination in Real Samples

An electrochemical sensor was developed by modifying a glassy carbon electrode (GCE) with functionalized multiwalled carbon nanotubes (FMWCNTs). The fabricated electrode was used to examine the redox behavior of carbendazim (CAR) in different pH solutions (pH 1.0–13.0). Surface morphology of the modified film was studied by scanning electron microscopy (SEM). An electroanalytical procedure for the determination of CAR was developed by adsorptive differential pulse stripping voltammetry (DPSV) over the range 0.01–5 × 10⁴ µ g L^?1. The developed procedure was also validated in real samples such as soil and water samples, and the applicability of the reported method is highly encouraging.     

Electrochemical detection of selenium using glassy carbon electrode modified with reduced graphene oxide

In this work, a simple experimental procedure was reported for the electroanalytical determination of selenium (IV) using reduced graphene oxide (rGO) to modify glassy carbon electrode (GCE). The rGO was obtained by reduction of graphene oxide obtained via Hummer’s method. The synthesised rGO was characterised using X-ray diffraction, Raman spectroscopy, scanning electron microscope (SEM), energy-dispersive spectroscopy and transmission Electron microscopy (TEM). GCE was modified with rGO and the electrochemical properties of the bare and modified electrode were investigated using cyclic voltammetry and electrochemical impedance spectroscopy. The results obtained showed that the modified electrode exhibited more excellent electrochemical properties than the bare GCE. The optimum conditions for detection of selenium in water using square wave anodic stripping voltammetry were as follows: deposition potential ?500 mV, pH 1, pre-concentration time of 240 s and 0.1 M nitric acid was used as supporting electrolyte. The linear regression equation obtained was I (µA) = 0.8432C + 9.2359 and the detection limit was calculated to be 0.85 μg L^?1. However, Cu(II) and Cd(II) are the two cations that interfered in the analysis of selenium in water.

The sensor was also applied for real sample water analysis and the result obtained was affirmed with inductively coupled plasma optical emission spectroscopic method. It is believed that our proposed sensor hold promise for practical application.     

阿奇霉素在多壁碳纳米管修饰电极上的电化学行为及其测定

运用循环伏安法与线性扫描伏安法研究了阿奇霉素在多壁碳纳米管修饰玻碳电极上的电化学行为,建立了一种直接测定阿奇霉素的电化学分析方法。结果表明,与裸玻碳电极相比,多壁碳纳米管修饰电极能显著提高阿奇霉素的氧化峰电流,阿奇霉素的电极过程完全不可逆,存在典型的吸附特性。在优化的实验条件下,氧化峰电流与阿奇霉素浓度在3.0×10-7～2.5×10-5 mol/L和2.5×10-5～5.0×10-4 mol/L范围内呈现良好的线性关系,检出限为1.0×10-7 mol/L。     

A novel electrochemical sensor for determination of hydroquinone in water using FeWO4/SnO2 nanocomposite immobilized modified glassy carbon electrode

A novel electrochemical sensor based on iron tungstate doped tin oxide nanocomposite Nafion (FeWO₄/SnO₂/Nf) immobilized modified glassy carbon electrode (GCE) is fabricated to determine hydroquinone (HQ) in this present study. The structural morphology and phase of FeWO₄/SnO₂ nanocomposite are characterized by X-ray powder diffraction (XRD), energy dispersive X-ray analysis (EDX), Fourier transform infrared spectroscopy (FT-IR), high transmission electron microscopy (HR-TEM) and Field emission scanning electron microscopy (FE-SEM), Brunauer-Emmett-Teller (BET) and X-ray photoelectron spectroscopy (XPS) respectively. Electrochemical methods such as cyclic voltammetry (CV), difference pulse voltammetry (DPV) and amperometric (i-t curve) are used to describe the electrochemical performance of the surface modified electrode for HQ sensing studies. The FeWO₄/SnO₂/Nf immobilized GCE is exhibited excellent catalytic activity with the increasing current signal during HQ sensing. The linear range of response is obtained between 0.01 µM and 50 µM for HQ detection under optimized conditions and the low detection limit (LOD) is found to be 0.0013 µM. Moreover, the present modified electrode shows good reproducibility and excellent anti-interference behavior. In addition, the present electrochemical sensor is applied to the real samples of collected waters from various sources and the obtained experimental results are quite satisfactory.     

Anodic stripping voltammetry of silver(I) using a carbon paste electrode modified with multi-walled carbon nanotubes

We describe a silver(I)-selective carbon paste electrode modified with multi-walled carbon nanotubes and a silver-chelating Schiff base, and its electrochemical response to Ag(I). Effects of reduction potential and time, accumulation time, pH of the solution and the stripping medium were studied by differential pulse anodic stripping voltammetry and optimized. The findings resulted in a method for the determination of silver over a linear response range (from 0.5 to 235 ng?mL^?1) and with a detection limit as low as 0.08 ng?mL^?1. The sensor displays good repeatability (with the RSD of ±?2.75 % for 7 replicates) and was applied to the determination of Ag(I) in water samples and X-ray photographic films.

Sensitive voltammetric assay of etoposide using modified glassy carbon electrode with a dispersion of multi-walled carbon nanotube

A sensitive electroanalytical method for the determination of anticancer drug etoposide (ETP) using adsorptive stripping differential pulse voltammetry (AdSDPV) at a multi-walled carbon nanotube-modified glassy carbon electrode (MWCNT-modified GCE) is presented. The surface morphology of modified electrode was characterized by scanning electron microscopy. The effects of accumulation time and potential, pH, scan rate, and amount of MWCNT suspension were investigated. The calibration curve was linear in the concentration range of 2.0?×?10^?8–2.0?×?10^?6 M with the detection limit of 5.4?×?10^?9 M. The reproducibility of the peak current was found at 1.55 % (n?=?5) RSD value in pH 6.0 Britton–Robinson buffer for the MWCNT-modified GCE. The method was then successfully utilized for the determination of ETP in pharmaceutical dosage form, and a recovery of 99.55 % was obtained. The possible oxidation mechanism of ETP was also discussed. The proposed electroanalytical method using MWCNT-modified GCE is the most sensitive method for the determination of ETP with lowest limit of detection in the previously published electrochemical methods.     

Electrochemical determination of naproxen in the presence of acetaminophen using a carbon paste electrode modified with activated carbon nanoparticles

In this study, cyclic voltammetry and differential pulse voltammetry were used to determine the electrochemical properties and concentration of naproxen in pharmaceutical formulation and human serum samples by using a carbon paste electrode modified with activated carbon nanoparticles. Optimum conditions were obtained at an electrode with 0.005 g activated carbon nanoparticles in a phosphate buffer solution of pH 6 as a supporting electrolyte. Linear calibration curves were obtained in the range of 0.1–120 μM, and the detection limit of naproxen determined was 0.0234 μM. The modified electrode shows good selectivity for naproxen in the presence of some organic and inorganic interferences and very good precision in real samples. Finally, naproxen was measured in the presence of acetaminophen.     

The determination of acetaminophen using a carbon nanotube:graphite-based electrode

The oxidation of acetaminophen was studied at a glassy carbon electrode modified with multi-walled carbon nanotubes and a graphite paste. Cyclic voltammety, differential pulse voltammetry and square wave voltammetry at various pH values, scan rates, and the effect of the ratio of nanotubes to graphite were investigated in order to optimize the parameters for the determination of acetaminophen. Square wave voltammetry is the most appropriate technique in giving a characteristic peak at 0.52 V at pH 5. The porous nanostructure of the electrode improves the surface area which results in an increase in the peak current. The voltammetric response is linear in the range between 75 and 2000 ng.mL^?1, with standard deviations between 0.25 and 7.8%, and a limit of detection of 25 ng.mL^?1. The method has been successfully applied to the analysis of acetaminophen in tablets and biological fluids.     

Determination of microcystin-LR with a glassy carbon impedimetric immunoelectrode modified with an ionic liquid and multiwalled carbon nanotubes

We report on a sensitive, simple, label-free impedance-based immunoelectrode for the determination of microcystin-LR (MCLR). The surface of the electrode was modified with a composite made from multiwalled carbon nanotubes and an ionic liquid, and with immobilized polyclonal antibody against MCLR. Cyclic voltammetry and impedance spectroscopy were applied to characterize the modified electrode. It is found that the multi-walled carbon nanotubes act as excellent mediators for the electron transfer between the electrode and dissolved hexacyanoferrate redox pair, while the ionic liquid renders it biocompatible. The method exhibits a wide linear range (0.005 μg?L-1 to 1.0 μg?L-1), a low detection limit (1.7 ng?L-1) and a long-term stability of around 60 days. The ionic liquid 1-amyl-2,3-dimethylimidazolium hexafluorophosphate gave the best impedimetric response. The new immunoelectrode is sensitive, stable, and easily prepared. It has been successfully applied to the determination of MCLR in water samples.

Voltammetric and amperometric determination of uric acid at a carbon-ceramic electrode modified with multi walled carbon nanotubes

The voltammetric behavior of uric acid (UA) was studied at a carbon-ceramic electrode modified with multi walled carbon nanotubes; which was developed via a simple procedure. UA can be effectively oxidized at the surface of the electrode and produced an anodic peak at about 0.29 V in pH 6.8 phosphate buffer solutions. The experimental parameters such as pH, accumulation time, and amount of multi walled carbon nanotubes were optimized for determination of UA. Under the optimum conditions, the anodic peak current in differential pulse voltammetry is linear to the UA concentration over the range from 2.5×10?7M to 1.0×10?4 M with a correlation coefficient of 0.998. The electrode exhibited good stability and could be easily regenerated. The relative standard deviation of the peak current obtained for a 5.0?×?10^?5 M UA solution was 1.0%. The influence of dopamine and ascorbic acid on the anodic peak current of UA was examined. This method was successfully applied for the determination of uric acid in human urine sample, and the recovery was 99.9%.     

Electroanalytical chemistry of chlorinated phenols at a glassy carbon electrode

The electroanalytical chemistry of chlorinated phenols at a glassy carbon electrode in various solvent—electrolyte media is described. Differential pulse voltammetry may be used to determine chlorinated phenols in a methanol—0.07 M sulfuric acid medium. The determination of pentachlorophenol in liquid formulations is described. Cyclic voltammetric Studies are used to investigate the electrochemical reaction mechanisms of chlorinated phenols. The electrochemical oxidation products of these compounds are quite reactive, and follow-up chemical reactions result in electrode filming under the conditions studied.     

A Fast and Simple Ozone‐mediated Method towards Highly Activated Screen Printed Carbon Electrodes as Versatile Electroanalytical Tools

A facile and effective electrochemical activation method of screen printed carbon electrodes (SPCEs) has been performed using ozone gas. Activated SPCEs showed relevant improvements in the electrochemical properties such as an impedance reduction and better electroanalytical outcomes. Such improved properties were attributed to the increase of the electroactive surface area and the functionalization of the electrode surface with carbon‐oxygen groups onto the carbonaceous ink surface. The optimized activation method consisted in the performance of a voltammetric cycle between ?2 and 2 V at 10 mV s^?1 in 0.1 M NaOH solution with constant ozone gas bubbling. This activation procedure takes 12 min, which allows its use routinely prior to the electrode modifications and electroanalytical measurements. The resulting activated SPCEs exhibited superior sensitivities towards hydrogen peroxide, acetaminophen, hydroquinone and dopamine. This methodology might be considered as a strategy to attain SPCEs with improved electroanalytical properties for multiple applications.     

Cyclic voltammetry determination of epinephrine with a carbon fiber ultramicroelectrode

A carbon fiber ultramicroelectrode was used for the electroanalytical determination of epinephrine in biological fluids (urine) by cyclic voltammetry. The ultramicroelectrode was subjected to an electrochemical pretreatment in order to improve the epinephrine adsorption on the electrode surface. With this preconcetration step, detection limits of 7.8 ng ml(-1) and determination limits of 27.6 ng ml(-1) can be reached. The method was contrasted with native fluorescence determination-similar results were obtained.     

Evaluation of a novel composite based on functionalized multi-walled carbon nanotube and iron phthalocyanine for electroanalytical determination of isoniazid

A novel platform for electroanalysis of isoniazid based on graphene-functionalized multi-walled carbon nanotube as support for iron phthalocyanine (FePc/f-MWCNT) has been developed. The FePc/f-MWCNT composite has been dropped on glassy carbon forming FePc/f-MWCNT/GC electrode, which is sensible for isoniazid, decreasing substantially its oxidation potential to +200 mV vs Ag/AgCl. Electrochemical and electroanalytical properties of the FePc/f-MWCNT/GC-modified electrode were investigated by cyclic voltammetry, electrochemical impedance spectroscopy, scanning electrochemical microscopy, and amperometry. The sensor presents better performance in 0.1 mol L^?1 phosphate buffer at pH 7.4. Under optimized conditions, a linear response range from 5 to 476 μmol L^?1 was obtained with a limit of detection and sensitivity of 0.56 μmol L^?1 and 0.023 μA L μmol^?1, respectively. The relative standard deviation for 10 determinations of 100 μmol L^?1 isoniazid was 2.5%. The sensor was successfully applied for isoniazid selective determination in simulated body fluids.     

Electrocatalytic oxidation of salicylic acid at a carbon paste electrode impregnated with cerium-doped zirconium oxide nanoparticles as a new sensing approach for salicylic acid determination

Cerium-doped zirconium oxide (Ce/ZrO₂) was introduced as a highly efficient electrocatalyst for electrooxidation of salicylic acid (SA). The electrocatalyst material was synthesized via co-precipitation of cerium and zirconium ions, and then the resulting solid was heat-treated at high temperature to create crystallized cerium-doped zirconium oxide nanoparticles. The obtained material was characterized by scanning electron microscopy and X-ray diffraction methods. The Ce/ZrO₂-modified carbon paste electrode (Ce/ZrO₂-CPE) exhibited a distinct oxidative peak for SA, whereas no signal was observed for SA at unmodified carbon paste electrode at the same experimental conditions. Cyclic voltammetry and electrochemical impedance spectroscopy were applied to investigate the electrocatalytic performance of the electrode and SA electrooxidation mechanism. Square wave voltammetry was used to capture the analytical signal of SA. The electrode composition was optimized to increase the SA signal. Using the optimized electrode, it became possible to determine SA in the concentration range of 5.0–1000.0 μM with detection limit of 1.1 μM (3S_b/m). The electrode showed very high sensitivity of 1013.5 μA mM^?1 cm^?2 which is remarkably better than the previously reported SA sensors. The proposed method was successfully applied for the determination of SA in human serum, milk, and pharmaceutical samples.     

Electrochemical Behavior of Hydroquinone at Poly (Acridine Orange)–Modified Electrode and Its Separate Detection in the Presence of o‐Hydroquinone and m‐Hydroquinone

Abstract

Poly (acridine orange) (PAO) film–modified electrode was prepared by the electrooxidation of Acridine orange on a glassy carbon electrode (GCE) for the detection of hydroquinone in the presence of o‐hydroquinone and m‐hydroquinone. The electrochemical behavior of hydroquinone on the modified electrode was investigated with respect to different solution acidity, scan rate, and accumulation time. A pair of sharp and well‐defined peaks was obtained at 0.45 and 0.42 V [vs. a saturated calomel electrode (SCE)] at the PAO film–modified electrode. The potential difference between this pair of cathodic and anodic peaks was decreased to only 30 mV as compared to the 241 mV that was obtained on the bare glassy carbon electrode (GCE). As to o‐hydroquinone and m‐hydroquinone, their corresponding oxidation peaks appeared at 0.55 V and 0.89 V (vs. SCE), respectively. The oxidation potential differences between these three isomers enabled the separate detection of hydroquinone. Under the optimum experimental situation, the oxidation peak current of hydroquinone was proportional to the concentration at the range of 6.8×10^?7–9.6×10^?5 M. The detection limit was been estimated as 3×10^?7 M with 130 s accumulation. This method was applied to the hydroquinone detection in tap water samples.     

Electrocatalytic Determination of the antibiotic Levofloxacin using modified carbon paste electrode with a poly-murexide thin film voltammetrically

In this work, a simple, cheap, sensitive, and selective modified carbon paste electrode is proposed for the electroanalytical determination of Levofloxacin (LEVO), the drug used to treat pneumonia caused by coronavirus. The electrochemical polymerization method was applied to create a thin poly-murexide film (POMUR) on the bare carbon paste electrode (BCPE) surface to enhance its electrocatalytic activity. The peak current response of LEVO obtained by POMUR/CPE was increased by 14.2 μA compared to BCPE. Scanning electron microscopy (SEM) and cyclic voltammetry (CV) techniques were employed to characterize BCPE and POMUR/CPE. Under the optimal experimental circumstances, the prepared sensor was capable of determining LEVO with a low limit of detection (LOD) of 7.18 nM (S/N = 3) for a linear dynamic range of 25 – 1 × 10³ nM utilizing differential pulse voltammetry (DPV). Moreover, the practical applicability of POMUR/CPE for determining LEVO in pharmaceutical formulations and biological samples (human serum) demonstrated high sensitivity and selectivity with a recovery of 95.08 – 100.5 %.     

Fast and Simple Electroanalytical Identification of Iron Oxides in Geological Samples Without Sample Pretreatment

Hematite, goethite and siderite were found in geological samples using a simple, fast and low cost electroanalytical technique called voltammetry of immobilized microparticles (VMP). A carbon paste electrode was carefully rubbed onto the studied samples (an iron ore and ferrous oolites) to attach some microparticles to the surface of the electrode, and subsequently a potential scan was performed in two aqueous media to obtain the voltammogram which might be considered as the fingerprint of the sample deposited on the electrode. Each peak was related to an electrode process on the electrode whose peak potential indicates the type of iron compound. All the results were confirmed by commonly used analytical techniques to detect the presence of the different phases. All of this makes VMP an analytical tool very useful to save time and reduce analysis costs for geologist.     

Solidified floating organic drop microextraction for determination of trace amounts of zinc in water samples by flame atomic absorption spectrometry

A glassy carbon electrode was prepared that was coated with a composite film containing electropolymerized poly(amidosulfonic acid) and multi-walled carbon nanotubes. It was used to study the electrochemical response of procaine by differential pulse voltammetry. The results indicate that the electrode exhibits a remarkable improvement in the oxidation peak of procaine, and this led to a simple and sensitive method for the electroanalytical determination of procaine. The peak current is proportional to the concentration of procaine from 80 nM to 1.0 µM. The detection limit is 25 nM (S/N?=?3). The modified electrode was successfully applied to the direct determination of procaine in pharmaceutical formulations.