Development of a New Voltammetric Methodology for the Determination of Ciprofloxacin in Beef Samples Using a Carbon Paste Electrode Modified with Nafion and Fullerenes

A sensitive, selective, and low cost electrochemical new methodology was developed for the quantification of ciprofloxacin (Cip) in beef samples by cyclic voltammetry and differential pulse voltammetry, using a CPE electrode modified with Nafion and Fullerenes (N−F/CPE). The optimum parameters for the composition of the N−F/CPE electrode are 0.19 g mineral oil, 0.01 g Nafion, 50 μL fullerene, and graphite powder 0.3 g. The electrochemical characterization was carried out by obtaining maximum anodic peak current associated with the oxidation of ciprofloxacin at 1.1 V, where the electrochemical process resulted to be irreversible and diffusion-controlled. The analytical characterization of the proposed methodology was carried out resulting in a LOD of 1.0 μmol L⁻¹, a LOQ of 3.0 μmol L⁻¹, a sensitivity of 0.37±0.006 μA/μmolL⁻¹, and repeatability of 5.38 %.     

Sensitive Voltammetric Determination of Bisphenol A Based on a Glassy Carbon Electrode Modified with Copper Oxide‐Zinc Oxide Decorated on Graphene Oxide

A highly sensitive and selective chemical sensor was prepared based on metallic copper‐copper oxides and zinc oxide decorated graphene oxide modified glassy carbon electrode (Cu?Zn/GO/GCE) through an easily electrochemical method for the quantification of bisphenol A (BPA). The composite electrode was characterized via scanning electron microscopy (SEM), X‐Ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). The electrochemical behavior of BPA in Britton‐Robinson (BR) buffer solution (pH 7.1) was examined using cyclic voltammetry (CV). Under optimized conditions, the square wave voltammetry (SWV) response of Cu?Zn/GO/GCE towards BPA indicates two linear relationships within concentrations (3.0 nmol L^?1?0.1 μmol L^?1 and 0.35 μmol L^?1?20.0 μmol L^?) and has a low detection limit (0.88 nmol L^?1). The proposed electrochemical sensor based on Cu?Zn/GO/GCE is both time and cost effective, has good reproducibility, high selectivity as well as stability for BPA determination. The developed composite electrode was used to detect BPA in various samples including baby feeding bottle, pacifier, water bottle and food storage container and satisfactory results were obtained with high recoveries.     

Time Resolved Direct Determination of Arsenate in the Presence of Arsenite on Pencil Graphite Electrode Modified by Graphene Oxide and Zirconium

Trace amount of arsenate in the presence of arsenite was determined directly on pencil graphite electrode modified by graphene oxide and zirconium (Zr−G−PGE). The layer‐by‐layer modification of PGE was characterized by scanning electron microscopy (SEM), X‐ray photoelectron spectroscopy (XPS) and cyclic voltammetry (CV). Key point of the developed method was quick adsorption of arsenate than arsenite on the Zr−G−PGE. In optimal conditions, the Zr−G−PGE was applied for determination of arsenate using differential pulse voltammetry in a linear range 0.10–40.0 μg L⁻¹ with a limit of determination of 0.12±0.01 μg L⁻¹. The sensitivity of the electrode was 1.36±0.07 μA/μg L⁻¹. The modified electrode was used to measure the concentration of arsenate in the river water. A recovery test was performed by introducing 10 μg L⁻¹ arsenate into the rivers water in order and acceptable data of average recovery of 101.2 % was obtained. From the experimental results, the as‐prepared electrode can provide a satisfactory method for direct determination of arsenate in real samples.     

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.     

Gold Nanoparticles Stabilized in β‐Cyclodextrin and Decorated with Laccase Applied in the Construction of a Biosensor for Rutin

This paper describes the synthesis and characterization of gold nanoparticles stabilized in β‐cyclodextrin (AuNP‐CD), which were applied as a platform in the immobilization of laccase (LAC). The AuNP‐CD‐LAC were used in the construction of a new biosensor for rutin determination by square‐wave voltammetry (SWV). Under optimized conditions, the calibration curve showed a linear range for rutin of 0.30 to 2.97 μmol L⁻¹, with a limit of detection of 0.17 μmol L⁻¹. The biosensor demonstrated satisfactory repeatability and electrode‐to‐electrode repeatability (with relative standard deviations of 5.6 and 6.0 %, respectively) and good stability. The biosensor was successfully applied in the determination of rutin in different pharmaceutical samples.     

Simultaneous Determination of Hydroquinone and Catechol by Differential Alternative Pulses Voltammetry

The second order voltammetric technique of high resolution, Differential Alternative Pulses Voltammetry (DAPV), was applied for the simultaneous determination of hydroquinone (HQ) and catechol (CC) on bare spectroscopic graphite electrode. Well resolved anodic and cathodic peaks situated on both sides of the zero line were obtained, while the differential pulse voltammograms were overlapped. The linear concentration range for HQ and CC quantification by DAPV was extended up to 20 μmol L⁻¹ for both the isomers. The sensitivity of the determination was found to be 6.00 μA L μmol⁻¹ and 3.61 μA L μmol⁻¹, while the limit of detection reached was 0.2 μmol L⁻¹ and 0.5 μmol L⁻¹ for HQ and CC, respectively. No interference was observed from the commonly coexisting organic species such as resorcinol, phenol and p‐benzoquinone. The great resolution power of DAPV permitted obtaining excellent results without any electrode modification and any mathematical data processing.     

Electroanalytical Determination of Estrone in Seawater Samples Using Functionalized Multiwalled Carbon Nanotubes

In this work, a glassy carbon electrode (GCE) modified with multiwalled carbon nanotubes functionalized with carboxylic groups (MWCNT−COOH) was used to determine the hormone estrone in seawater samples. Modification of the electrode was optimized using three successive 10-μL aliquots of the MWCNT−COOH dispersion in ethanol (1 : 5 mL). The cyclic voltammetry results showed an oxidation peak at 0.59 V with characteristics of an irreversible process, pH dependent and controlled by adsorption of species. The results of square-wave voltammetry showed that the intensities of peak currents for the MWCNT−COOH/GCE were about 2.5 times higher than for GCE. The calibration curve showed a linearity of 0.9981 and a sensitivity of 0.1521 μA/mol L⁻¹. The limits of detection and quantification were 0.117 and 0.392 μmol L⁻¹, respectively. The recovery obtained using seawater samples was 91%, indicating the applicability of the method in marine environments.     

Development of an Electrochemical Sensor Based on Covalent Molecular Imprinting for Selective Determination of Bisphenol‐A

In this study, an electrochemical sensor was developed and used for selective determination of bisfenol‐A (BPA) by integrating sol‐gel technique and multi‐walled carbon nanotubes (MWCNTs) modified paste electrode. BPA bounded by covalently to isocyanatopropyl‐triethoxy silane (ICPTS) was synthesized as a new precursor (BPA‐ICPTS) and then BPA‐imprinted polymer (BPA‐IP) sol‐gel was prepared by using tetramethoxysilane (TMOS) and BPA‐ICPTS. Non‐imprinted polymer (NIP) sol‐gel was obtained by using TMOS and (3‐Aminopropyl) triethoxysilane. Both BPA‐IP and NIP sol‐gels were characterized by nitrogen adsorption‐desorption analysis, FTIR, SEM, particle size analyzer and optical microscope. Carbon paste sensor electrode was fabricated by mixing the newly synthesized BPA‐IP with MWCNTs, graphite powder and paraffin oil. The electrochemical characterization of the sensor electrode was achieved with cyclic and differential pulse voltammetric techniques. The response of the developed sensor under the most proper conditions was linear in BPA concentration range from 4.0×10⁻⁹ to 1.0×10⁻⁷ mol L⁻¹ and 5.0×10⁻⁷ to 5.0×10⁻⁵ mol L⁻¹ and the detection limit was 4.4×10⁻⁹ mol L⁻¹. The results unclosed that the proposed sensor displayed high sensitivity and selectivity, superior electrochemical performance and rapid response to BPA.     

Simple and Fast Determination of Warfarin in Pharmaceutical Samples Using Boron‐doped Diamond Electrode in BIA and FIA Systems with Multiple Pulse Amperometric Detection

This paper proposes the use of the boron‐doped diamond electrode (BDDE) in flow and batch injection analysis (FIA and BIA) systems with multiple‐pulse amperometric (MPA) detection for the determination of warfarin (WA) in pharmaceutical formulations. The electrochemical behavior of WA obtained by cyclic voltammetry (CV) in 0.1 mol L⁻¹ phosphate buffer shows an irreversible oxidation process at +1.0 V (vs Ag/AgCl). The MPA was based on the application of two sequential potential pulses as a function of time on BDDE: (1) for WA detection at +1.2 V/100 ms and; (2) for electrode surface cleaning at −0.2 V/200 ms. Both hydrodynamic systems (FIA‐MPA and BIA‐MPA) used for WA determination achieved high precision (with relative standard deviations around 2 %, n =10), wide linear range (2.0−400.0 μmol L⁻¹), low limits of detection (0.5 μmol L⁻¹) and good analytical frequency (94 h⁻¹ for FIA and 130 h⁻¹ for BIA). The WA determination made by the proposed methods was compared to the official spectrophotometric method. The FIA‐MPA and BIA‐MPA methods are simple and fast, being an attractive option for WA routine analysis in pharmaceutical industries.     

Electroanalysis of the Anthelmintic Drug Bithionol at Edge Plane Pyrolytic Graphite Electrode

An electrochemical study of the anthelmintic drug bithionol using edge plane pyrolytic graphite electrode (EPPGE) is presented for the first time by applying different electrochemical techniques, such as cyclic voltammetry (CV), square‐wave voltammetry (SWV), square‐wave adsorptive stripping voltammetry (SWAdSV), and alternating current (AC) impedance spectroscopy. Mechanistic aspects of the electrode reaction were studied implying a quasireversible electrode reaction from an adsorbed state of the reactant, coupled with a follow‐up chemical reaction to a final electroinactive product. The overall mechanism appears totally irreversible under conditions of CV at moderate scan rate, while being quasireversible under conditions of the fast SWV. Furthermore, an optimisation of the analytical procedure for quantitative determination of bithionol was conducted by applying SWV in an adsorptive stripping mode. The calibration curve was constructed in the concentration range of 0.1–1.0 μmol L^?1 (R²=0.9984) with a sensitivity of 3.6 μA L μmol^?1 and LOD of 26.7 nmol L^?1. The simple and sensitive SWAdSV procedure was proved to be suitable for the analysis of spiked urine samples.     

Voltammetric Method for the Simultaneous Determination of Melatonin and Pyridoxine in Dietary Supplements Using a Cathodically Pretreated Boron‐doped Diamond Electrode

The simultaneous voltammetric determination of melatonin (MT) and pyridoxine (PY) has been carried out at a cathodically pretreated boron‐doped diamond electrode. By using cyclic voltammetry, a separation of the oxidation peak potentials of both compounds present in mixture was about 0.47 V in Britton‐Robinson buffer, pH 2. The results obtained by square‐wave voltammetry allowed a method to be developed for determination of MT and PY simultaneously in the ranges 1–100 μg mL⁻¹ (4.3×10⁻⁶–4.3×10⁻⁴ mol L⁻¹) and 10–175 μg mL⁻¹ (4.9×10⁻⁵–8.5×10⁻⁴ mol L⁻¹), with detection limits of 0.14 μg mL⁻¹ (6.0×10⁻⁷ mol L⁻¹) and 1.35 μg mL⁻¹ (6.6×10⁻⁶ mol L⁻¹), respectively. The proposed method was successfully to the dietary supplements samples containing these compounds for health‐caring purposes.     

Electrocatalytic and Simultaneous Determination of Ascorbic Acid,Nicotinamide Adenine Dinucleotide and Folic Acid at Ruthenium(II) Complex‐ZnO/CNTs Nanocomposite Modified Carbon Paste Electrode

This paper describes the development a novel ruthenium(II) complex‐ZnO/CNTs modified carbon paste electrode (Ru(II)/ZnO/CNTs/CPE) for the electrocatalytic determination of ascorbic acid (AA). The objective of this novel electrode modification was to seek new electrochemical performances for the detection of AA, nicotinamide adenine dinucleotide (NADH) and folic acid (FA). The peak potentials recorded were 170, 500 and 830 mV vs. Ag/AgCl/KCl_sat for AA, NADH and FA, respectively. The peak currents were linearly dependent on AA, NADH and FA concentrations using square wave voltammetry (SWV) method at the ranges of 0.008–251, 1.0–650, and 3.0–700 µmol L^?1, with detection limits of 0.005, 0.5, and 1.0 µmol L^?1, respectively.     

Synthesis of Silver Nanoparticle‐Graphene Composites for Electroanalysis Applications using Chemical and Electrochemical Methods

An electrochemical device was developed for the simultaneous determination of sulfamethoxazole (SMX) and trimethoprim (TMP) using differential pulse voltammetry and glassy carbon (GC) electrodes modified with reduced graphene oxide (rGO) and silver nanoparticle (AgNP) composites, synthesised using both chemical and electrochemical methods. The morphology and electrochemical behaviour of the GC electrodes modified with the rGO/AgNP (chemical method) and rGO‐AgNP (electrochemical method) composites were characterised by scanning electron microscopy and cyclic voltammetry. These techniques demonstrated that, in both methods, the graphene oxide was modified by the AgNPs, and the composite synthesised by the electrochemical method showed a better dispersion of the nanoparticles, resulting in an increase in the surface area compared to the rGO/AgNP composite. The GC/rGO‐AgNP electrode was evaluated and optimised for the simultaneous determination of SMX and TMP, achieving detection limits of 0.6 μmol L⁻¹ for the SMX and 0.4 μmol L⁻¹ for the TMP. The proposed GC/rGO‐AgNP electrochemical device was successfully applied to the simultaneous determination of SMX and TMP in wastewaters samples.     

Stripping Voltammetric Determination of Methyl Parathion at Activated Carbon Nanopowder Modified Electrode

An activated carbon nanopowder modified glassy carbon electrode (AC-GCE) was constructed for the sensitive determination of methyl parathion by adsorptive differential pulse anodic stripping voltammetry. The simple and rapid modification procedure included only drop-coating the electrode surface with a laponite stabilized activated carbon nanopowder suspension and drying. The modifier high adsorption ability, combined with its large electroactive surface area allowed a 30-fold signal increase to be achieved, compared to bare GCE. Under optimized experimental conditions (activated carbon to laponite ratio, pH and accumulation time), the AC-GCE exhibited a linear response to methyl parathion in two concentration ranges: from 0.01 μmol L⁻¹ to 1 μmol L⁻¹ and from 1 μmol L⁻¹ to 6 μmol L⁻¹. The LOD of 2.5 nmol L⁻¹ (S/N=3) achieved fitted with regulatory norms. It was demonstrated that the as-prepared AC-GCE is suitable for routine real samples analysis.     

Glassy Carbon Electrode Modified with Layering of Carbon Black/Poly(Allylamine Hydrochloride) Composite for Multianalyte Determination

An electrochemical sensor using glassy carbon electrode modified with carbon black within a poly(allylamine hydrochloride) film is proposed in this work. The novel sensor was characterized by scanning electron microscopy, electrochemical impedance spectroscopy, and cyclic voltammetry using the redox probe Fe(CN)6^3−/4−. The sensor was applied for the simultaneous determination of dopamine (DA), paracetamol (PAR), amlodipine (AML), and rosuvastatin (RSV). The quantification of all four analytes was carried out by linear sweep voltammetry and presented a linear concentration range for all analytes from 1.0 to 90 μmol L⁻¹, with limit of detection of 0.55, 1.3, 5.7, and 3.0 μmol L⁻¹ for DA, PAR, AML, and RSV, respectively. This sensor was successfully applied in the simultaneous determination of these analytes in environmental, pharmaceutical, and biological samples.     

Development of a Sensor Based on Modified Carbon Paste with Com Iron(III) Protoporphyrin Immobilized on SiNbZn Silica Matrix for L‐tryptophan Determination

In this work, SiO₂/Nb₂O₅/ZnO prepared by the sol‐gel processing method was used as substrate base for immobilization of the protoporphyrin‐IX ion. Iron(III) ion was inserted into the porphyrin ring (SiNbZn‐PPFe). A simple square wave voltammetry method based on a composite sensor carbon paste electrode of this material,designed as EPC‐SiNbZn‐PPFe, was developed and validated successfully for the determination of L‐tryptophan (Trp). The optimum conditions were obtained by using sensor modified with 18.00 mg SiNbZn‐PPFe material, 12.00 mg graphite powder and 6.0 μL mineral oil and phosphate buffer 0.3 mol L⁻¹ pH 7.0. The sensitivity of the sensor was found to be 0.523 AL mol ⁻¹, linear range from 10 to 70 μmol L⁻¹ and limit of detection of 3.28 μmol L⁻¹. Therefore, the developed method was successfully applied for the Trp determination in real samples of pharmaceutical formulation and can be used for routine quality control pharmaceutical formulations containing Trp.     

A Newly Competitive Electrochemical Sensor for Sensitive Determination of Chrysin Based on Electrochemically Activated Ta2O5 Particles Modified Carbon Paste Electrode

A novel electrochemically activated doped Ta₂O₅ particles modified carbon paste electrode (EA‐Ta₂O₅‐CPE) was prepared and applied for selective and sensitive determination of chrysin. X‐ray diffraction (XRD), scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS) techniques and cyclic voltammetry (CV) were used to characterize the Ta₂O₅ particles and investigate the electrochemical response of the sensor. Compared with bare CPE, the doped Ta₂O₅ modified electrode got much more porous by electrochemical treatment and exhibited larger effective surface area, more reactive site and excellent electrochemical catalytic activity toward the oxidation of chrysin. Under optimum conditions by LSV, the oxidation peak currents responded to chrysin linearly over a concentration range from 5.0×10⁻⁸ to 7.0×10⁻⁶ mol L⁻¹ with a detection limit of 2.0×10⁻⁸ mol L⁻¹ (5.08 ng mL⁻¹). The fabricated sensor showed anti‐interference ability against the biological common interferents (i.e. baicalein, baicalin) and provided to be reliable for the determination of chrysin in Chinese medicinal herb Oroxylum indicum and chrysin capsules samples with satisfactory results.     

Nanostructured Hexacyanoferrate Intercalated Ni/Al Layered Double Hydroxide Modified Electrode as a Sensitive Electrochemical Sensor for Paracetamol Determination

An electrochemical sensor for paracetamol (PC) based on the hexacyanoferate(III) intercalated Ni−Al layered double hydroxide (Ni−Al−HCF) was presented. The as‐prepared LDH structurally and morphologically was characterized by scanning electron microscopy, X‐ray diffraction, and Fourier transform IR. Electrochemical studies revealed that Ni−Al−HCF film modified glassy carbon (GC) electrode exhibited remarkable electrocatalytic activity toward the oxidation of paracetamol. The electrochemical behavior of PC on the Ni−Al−HCF film was investigated in detail. Under optimum experimental conditions, the electrocatalytic response of the modified GC electrode was linear in the PC concentration range 3×10⁻⁶⁻–1.5×10⁻³ mol L⁻¹, with a detection limit of 8×10⁻⁷ mol L⁻¹ (S/N=3), using hydrodynamic amperometry. In addition, the modified electrode exhibited good reproducibility, long‐term stability and anti‐interference property. The fabricated sensor was successfully applied to determination of PC in various pharmaceutical preparations such as tablets, oral solution, and oral drops. Finally, the method was validated by the analysis of paracetamol spiked human serum samples, and good recoveries were obtained in the range of 99.2–103 %.     

Effect of Different Carbon Blacks on the Simultaneous Electroanalysis of Drugs as Water Contaminants Based on Screen‐printed Sensors

For the construction of the sensor, three different carbon black (CB) materials (VULCAN XC72R, BLACK PEARLS 4750 and CB N220) were explored as modifying nanomaterial. Firstly, the electrochemical activity of the each SPE modified was compared by cyclic voltammetry and electrochemical impedance spectroscopy technique, using [Fe(CN)₆]^3?/4? as redox couple. After demonstrating that electrodes modified with different types of CB were characterized by improved electrochemical performances when compared with bare electrodes, and among them, electrodes modified with CB BP4750 is characterised by slightly better electrochemical properties, this type of electrode was used for the development of the analytical method. By applying SWV technique in 0.2 mol L^?1 phosphate buffer (pH 3.0), the obtained analytical curves for ACP and LVF were found linearly from 4.0 to 80.0 μmol L^?1 and from 0.90 to 70.0 μmol L^?1 with limit of detection of 2.6 μmol L^?1 and 0.42 μmol L^?1 for ACP and LVF, respectively. Finally, the quantification of these drugs in river water was evaluated using the new here‐proposed sensor by recovery method in spiked samples, obtaining satisfactory recovery values. The results achieved demonstrated that the developed analytical tool is of great analytical interest being easy to use, cost‐effective, miniaturized, and thus suitable for low cost on site analysis.     

Electrocatalytic oxidation and the mechanism of dopamine on a MWNT-modified glassy carbon electrode

The electrochemical behavior of dopamine (DA) at a MWNTs-modified glassy carbon electrode was investigated by cyclic voltammetry (CV), square wave voltammetry (SWV). The MWNTs modified electrode exhibited marked promotion of the electrochemical reaction of DA in different environments. Under optimum conditions, the peak currents of SWV of DA were increased linearly with incremental concentration of DA in the range from 5 × 10^?7 to 1 × 10^?5 mol L^?1. The limit of detection is 3 × 10^?7 mol L^?1.