Utilization of Carbon Paste Electrodes for the Voltammetric Determination of Chlortoluron

Conventional (CPE) and miniaturized (m‐CPE) carbon paste electrodes consisting of a carbon paste filled capillary were used for differential pulse voltammetric determination of chlortoluron in samples of river water and soil, in the latter case after the extraction by methanol. Britton‐Robinson buffer pH 3 with low content of methanol was found to be optimal for the determination. The achieved determination limits were 2.8 µmol L^?1 and 0.34 µmol L^?1 in river water, and 3.1 and 4.3 µg g^?1 in soil, using CPE and m‐CPE, respectively.     

A Novel Voltammetric Method for the Determination of Maleic Acid Using Silver Amalgam Paste Electrode

An efficient voltammetric method was developed for the determination of maleic acid at a silver amalgam paste electrode (AgA‐PE) in Britton–Robinson buffer pH 2.0. The experimental parameters, such as pH of Britton–Robinson buffer, type of the supporting electrolyte and activation of the electrode surface were optimized. Under the optimal conditions, a linear response was observed over the 2×10^?6–1×10^?4 mol L^?1 maleic acid concentration range, determination limit being 5×10^?7 mol L^?1. A highly stable response, with a relative standard deviation (RSD) of 1.6% for 45 repetitive measurements of 1×10^?4 mol L^?1 maleic acid showed that there was no apparent surface passivation indicating the suitability of the method. The method was successfully applied for direct determination of maleic acid in drinking and river water.     

Electrochemical Behaviors of Adenosine‐5′‐triphosphate on Molecular Wire Modified Carbon Paste Electrode and Its Sensitive Detection

A new electrochemical method was proposed for the determination of adenosine‐5′‐triphosphate (ATP) based on the electrooxidation at a molecular wire (MW) modified carbon paste electrode (CPE), which was fabricated with diphenylacetylene (DPA) as the binder. A single well‐defined irreversible oxidation peak of ATP appeared on MW‐CPE with adsorption‐controlled process and enhanced electrochemical response in a pH 3.0 Britton‐Robinson buffer solution, which was due to the presence of high conductive DPA in the electrode. The electrochemical parameters of ATP were calculated with the electron transfer coefficient (α) as 0.54, the electron transfer number (n) as 1.9, the apparent heterogeneous electron transfer rate constant (k_s) as 2.67 × 10^?5 s^?1 and the surface coverage (Γ_T) as 4.15 × 10^?10 mol cm^?2. Under the selected conditions the oxidation peak current was proportional to ATP concentration in the range from 1.0 × 10^?7 mol L^?1 to 2.0 × 10^?3 mol L^?1 with the detection limit as 1.28 × 10^?8 mol L^?1 (3σ) by sensitive differential pulse voltammetry. The proposed method showed good selectivity without the interferences of coexisting substances and was successful applied to the ATP injection samples detection.     

Flow Injection Analysis of Maleic Hydrazide Using an Electrochemical Sensor Based on Palladium‐Dispersed Carbon Paste Electrode

A new analytical methodology for the electrochemical detection of the herbicide maleic hydrazide (3,6‐dihydroxypyridazine) by flow injection analysis is presented. This method is supported by the novel application of a palladium‐dispersed carbon paste electrode as an amperometric sensor for this herbicide. Maleic hydrazide shows anodic electrochemical activity on carbon‐based electrodes (glassy carbon or carbon paste electrodes) in all the pH range. This electrochemical activity is enhanced using metal‐dispersed carbon paste electrodes, especially at Pd‐dispersed CPE which displays good oxidation signals at 690 mV (0.050 M phosphate buffer pH 7.0), 140 mV lower than at unmodified electrodes. Under the optimized conditions, the electroanalytical performance of Pd‐dispersed CPE in flow injection analysis was excellent, with good reproducibility (RSD 3.3%) and a wide linear range (1.9×10^?7 to 1.0×10^?4 mol L^?1). A detection limit of 1.4×10^?8 mol L^?1 (0.14 ng maleic hydrazide) was obtained for a sample loop of 100 μL at a fixed potential of 700 mV in 0.050 M phosphate buffer solution at pH 7.0 and a flow rate of 2.0 mL min^?1. The proposed method was applied for the maleic hydrazide detection in natural drinking water samples.     

Ionic silsesquioxane film immobilized on silica applied in the development of carbon paste electrode for determination of methyl parathion

A mesoporous silica-based hybrid material composed of silica xerogel modified with an ionic silsesquioxane, which contains the 1,4-diazoniabicyclo[2.2.2]octane chloride group, was obtained. The silsesquioxane film is highly dispersed on the surface. This hybrid material was utilized to develop a carbon paste electrode (CPE) for determination of methyl parathion. Transmission FTIR, elemental analysis and N₂ adsorption–desorption isotherms were used for characterization of the material. The electrochemical behavior of methyl parathion was evaluated by cyclic voltammetry and differential pulse voltammetry. It was observed a linear response to methyl parathion in the concentration range from 1.25 × 10^?7 to 2.56 × 10^?6 mol L^?1 by employing the carbon paste electrode, in Britton–Robinson buffer solution (pH 6). The achieved detection limit (3 SD of the blank divided by the slope of calibration curve) was 0.013 µmol L^?1 and sensitivity was 6.3 µA µmol L^?1. This result shows the potentiality of this electrode for application as electrochemical sensor for methyl parathion.     

Electrochemical Oxidative Detection of Guanosine‐5′‐triphosphate Based on a New Ionic Liquid Modified Carbon Paste Electrode

An ionic liquid (IL) 1‐(3‐chloro‐2‐hydroxy‐propyl)‐3‐methylimidazolium trifluoroacetate was used as the modifier for the preparation of the modified carbon paste electrode (CPE). The IL‐CPE showed excellent electrocatalytic activity towards the oxidation of guanosine‐5′‐triphosphate (5′‐GTP) in a pH 5.0 Britton‐Robinson buffer solution. Due to the presence of high conductive IL on the electrode surface, the electrooxidation of 5′‐GTP was greatly promoted with a single well‐defined irreversible oxidation peak appeared. The electrode reaction was an adsorption‐controlled process and the electrochemical parameters of 5′‐GTP on IL‐CPE were calculated with the electron transfer coefficient (α) as 0.44, the electron transfer number (n) as 1.99, the apparent heterogeneous electron transfer rate constant (k_s) as 2.21 × 10^?9 s^?1 and the surface coverage (Γ_T) as 1.53 × 10^?10 mol cm^?2. Under the selected conditions a linear calibration curve between the oxidation peak currents and 5′‐GTP concentration was obtained in the range from 2.0 to 1000.0 μmol L^?1 with the detection limit as 0.049 μmol L^?1 (3σ) by differential pulse voltammetry. The proposed method showed good selectivity to the 5‘‐GTP detection without the interferences of coexisting substances and the practical application was checked by measurements of the artificial samples.     

Selective determination of cysteine in the presence of tryptophan by carbon paste electrode modified with quinizarine

A sensitive and selective electrochemical method for the determination of L-cysteine was developed using a modified carbon paste electrode (MCPE) with quinizarine. Cyclic voltammetry was used to investigate the redox properties of this modified electrode at various solution pH values and at various scan rates. The apparent charge transfer rate constant, ks and transfer coefficient for electron transfer between quinizarine and carbon paste electrode (CPE) were calculated as 2.76 s^?1 and 0.6, respectively. This modified carbon paste electrode shows excellent electrocatalytic activity toward the oxidation of L-cysteine in a phosphate buffer solution (pH 7.0). The linear range of 1.0 × 10^?6 to 1.0 × 10^?3 M and a detection limit (3s) of 2.2 × 10^?7 M were observed in pH 7.0 phosphate buffer solutions. In differential pulse voltammetry, the quinizarine modified carbon paste electrode (QMCPE) could separate the oxidation peak potentials of L-cysteine and tryptophan present in the same solution, though at the unmodified CPE the peak potentials were indistinguishable. This work introduces a simple and easy approach to selective detection of L-cysteine in the presence of tryptophan. Also, the modified electrode was employed for the determination of L-cysteine in the real samples such as serum of blood and acetylcysteine tablet.     

Development of carbon paste electrode modified with cadmium ion-imprinted polymer for selective voltammetric determination of Cd2+

A simple and fast voltammetric method based on a new electrode composed of carbon paste electrode/bifunctional hybrid ion imprinted polymer (CPE/IIP) was developed for the quantification of Cd²⁺ in water samples. The voltammetric measurements by Differential Pulse Voltammetry were performed by using CPE containing 11.0 mg of IIP under phosphate buffer solution at concentration 0.1 mol L^?1 and pH 6.5. The electrochemical method was carried out by Cd²⁺ preconcentration at ?1.2 V during 210 s, followed by anodic stripping. The performance of IIP towards Cd²⁺ determination was evaluated by comparison to non-imprinted polymer, whose detectability of IIP was much higher (45%). The sensitivity of the sensor was found to be 0.0105 µA/µg L^?1. The limits of detection and limits of quantification were found to be 4.95 μg L^?1 and 16.4 μg L^?1, respectively. The developed method was successfully applied to Cd²⁺ determination in mineral, tap and lake water samples, whose results are in agreement with thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS) used as reference analytical technique. According to achieved results, the developed method can be used for routine analysis of quality control of water samples from different sources.     

Electrochemical Behaviours and Detection of Adenosine‐5¢‐triphosphate on an Ionic Liquid Modified Carbon Paste Electrode

In this paper a new electrochemical method based on the ionic liquid modified carbon paste electrode (IL‐CPE) was proposed for the determination of adenosine‐5′‐triphosphate (ATP) in a pH 4.5 Britton‐Robinson (B‐R) buffer solution. IL‐CPE was prepared by using 1‐butyl‐3‐methylimidazolium trifluoroacetate (BMIMCF₃COO) as the modifier. Cyclic voltammetry was used to investigate the electrochemical behaviors of ATP on the IL‐CPE, and the results indicated that IL‐CPE exhibited strong electrocatalytic ability to promote the oxidation of ATP with a single well‐defined irreversible adsorption‐controlled oxidation peak appeared. The electrochemical reaction parameters of ATP were calculated with the results of the electron transfer coefficient (α) as 0.40, the electron transfer number (n) as 1.17, the apparent heterogeneous electron transfer rate constant (ks) as 3.66 × 10^‐6 s^‐1 and the surface coverage (Γ_τ) as 2.48 × 10^‐9 mol cm^‐2. Under the selected conditions the proposed IL‐CPE showed good performances to the ATP detection in the concentration range from 0.1 to 1000.0 μmol L^‐1 with the detection limit as 3.65 × 10^‐8 mol L^‐1 (3σ) by differential pulse voltammetry. The method showed good selectivity to the ATP detection without the interferences of coexisting substances and was successfully applied to the ATP injection samples detection with satisfactory results.     

Determination of three Tumor Biomarkers (Homovanillic Acid,Vanillylmandelic Acid,and 5‐Hydroxyindole‐3‐Acetic Acid) Using Flow Injection Analysis with Amperometric Detection

Flow injection analysis with amperometric detection (FIA‐AD) at screen‐printed carbon electrodes (SPCEs) in optimum medium of Britton‐Robinson buffer (0.04 mol ? L^?1, pH 2.0) was used for the determination of three tumor biomarkers (homovanillic acid (HVA), vanillylmandelic acid (VMA), and 5‐hydroxyindole‐3‐acetic acid (5‐HIAA)). Dependences of the peak current on the concentration of biomarkers were linear in the whole tested concentration range from 0.05 to 100 μmol ? L^?1, with limits of detection (LODs) of 0.065 μmol ? L^?1 for HVA, 0.053 μmol ? L^?1 for VMA, and 0.033 μmol ? L^?1 for 5‐HIAA (calculated from peak heights), and 0.024 μmol ? L^?1 for HVA, 0.020 μmol ? L^?1 for VMA, and 0.012 μmol ? L^?1 for 5‐HIAA (calculated from peak areas), respectively.     

Differential Pulse Voltammetric Determination of 2‐Methyl‐4,6‐Dinitrophenol using Bismuth Bulk Electrode

This work reports the application of bismuth bulk electrode (BiBE) for the determination of 2‐methyl‐4,6‐dinitrophenol (MDNP) by differential pulse voltammetry (DPV) in Britton‐Robinson buffer of pH 12.0 as an optimal medium. BiBE was prepared by transferring molten bismuth into a glass tube under constant stream of nitrogen. The linear concentration dependences were measured from 1 to 10 μmol ? L^?1 and from 10 to 100 μmol ? L^?1 by using optimum accumulation potential of ?0.7 V and optimum accumulation time 30 s. Under these conditions limit of determination and limit of quantification was 0.45 and 1.5 μmol ? L^?1, respectively. The developed method was successfully applied for the analysis of tap water as a model sample.     

Validated Voltammetric Method for the Simultaneous Determination of Anti‐diabetic Drugs,Linagliptin and Empagliflozin in Bulk,Pharmaceutical Dosage Forms and Biological Fluids

A cobalt oxide nanoparticles (Co₃O₄NPs) and multi walled carbon nanotubes (MWCNTs) modified carbon paste electrodes were used to study the electrochemical behavior of linagliptin and empagliflozin in Britton Robinson buffer solution of pH 8.0 using cyclic and square wave voltammetry. The above mentioned modified electrodes showed highly sensitive sensing and gave an excellent anodic response for both drugs. The peak current varied linearly over the concentration ranges: 3.98×10^?5–1.53×10^?3 mol L^?1 (18.82–723.00 μg/mL) and 7.94×10^?6–1.07×10^?4 mol L^?1 (3.65–48.25 μg/mL) with determination coefficients of 0.9999 and 0.9998 for linagliptin and empagliflozin, respectively. The recoveries and relative standard deviations were found in the following ranges: 98.80 %–102.00 % and 0.23 %–1.90 % for linagliptin and 98.30 %–101.80 % and 0.11 %–1.86 % for empagliflozin. The detection and quantification limits were 1.13×10^?5 and 3.76×10^?5 mol L^?1 (5.34and17.77 μg/mL) for linagliptin, 1.71×10^?6and 5.68×10^?6 mol L^?1 (0.77 and 2.56 μg/mL) for empagliflozin. The proposed sensors have been successfully applied for the determination of the drugs in bulk, pharmaceutical formulations and biological fluids.     

Electrochemical oxidation behavior of methotrexate at DNA/SWCNT/Nafion composite film-modified glassy carbon electrode

Glassy carbon electrode modified with DNA-functionalized single-walled carbon nanotube (DNA/SWCNT) and Nafion composite film was developed for the detection of methotrexate. The characteristics of the modified electrode were examined by transmission electron microscopy and cyclic voltammetry. Compared with a bare glassy carbon electrode and Nafion- and SWCNT/Nafion-modified electrodes, the DNA/SWCNT/Nafion-modified one exhibited the more superior ability of detecting methotrexate, including the higher sensitivity and the lower overpotentials, due to the synergetic DNA-functionalized SWCNT and Nafion. Also, the dependence of the current on pH, nature of buffer, instrumental parameters, accumulation time, and potential was investigated to optimize the experimental conditions in the determination of methotrexate. Under the selected conditions, the modified electrode in pH?=?2.78 Britton–Robinson buffer solutions showed a linear voltammetric response to methotrexate within the concentration range of 2.0?×?10^?8–1.5?×?10^?6?mol?L^?1, with the detection limit of 8.0?×?10^?9?mol?L^?1. The method was also applied to detect methotrexate in medicinal tablets and spiked human blood serum samples.     

Voltammetric Determination of Cymoxanil and Famoxadone at Different Types of Carbon Electrodes

Differential pulse voltammetry (DPV) at a carbon fibre rod electrode (CFRE) and a capillary carbon paste electrode (CPE) have been used for the determination of pesticides cymoxanil and famoxadone, respectively. In the cathodic potential range, optimum conditions were found for the determination of cymoxanil by DPV at CFRE at pH 4 with limit of quantification (L_Q) of 5.9×10^?7 mol L^?1. In the anodic area, determination of famoxadone by DPV at CPE was performed at optimum pH 2 with L_Q=1.4×10^?7 mol L^?1. Practical applicability of the newly developed methods was verified on spiked samples of river water and soil.     

Electrochemical Behavior of 8‐Azaguanine at DNA Langmuir–Blodgett Modified Glassy Carbon Electrode and Its Analytical Application

A highly sensitive electrochemical biosensor for the detection of trace amounts of 8‐azaguanine has been designed. Double stranded (ds)DNA molecules are immobilized onto a glassy carbon electrode surface with Langmuir–Blodgett technique. The adsorptive voltammetric behaviors of 8‐azaguanine at DNA‐modified electrode were explored by means of cyclic voltammetry and square wave voltammetry. Compared with bare glassy carbon electrode (GCE), the Langmuir–Blodgett film modified electrode can greatly improve the measuring sensitivity of 8‐azaguanine. Under the optimum experimental conditions, the Langmuir–Blodgett film modified electrode in pH 3.0 Britton–Robinson buffer solutions shows a linear voltammetric response in the range of 5.0×10^?8 to 1.0×10^?5 mol L^?1 with detection limit 9.0×10^?9 mol L^?1. The method proposed was applied successfully for the determination of 8‐azaguanine in diluted human urine with wonderful satisfactory.     

Electrochemical Determination of the Herbicide Bentazone Using a Carbon Nanotube β‐Cyclodextrin Modified Electrode

An electrochemical sensor has been developed for the determination of the herbicide bentazone, based on a GC electrode modified by a combination of multiwalled carbon nanotubes (MWCNT) with β‐cyclodextrin (β‐CD) incorporated in a polyaniline film. The results indicate that the β‐CD/MWCNT modified GC electrode exhibits efficient electrocatalytic oxidation of bentazone with high sensitivity and stability. A cyclic voltammetric method to determine bentazone in phosphate buffer solution at pH 6.0, was developed, without any previous extraction, clean‐up, or derivatization steps, in the range of 10–80 µmol L^?1, with a detection limit of 1.6 µmol L^?1 in water. The results were compared with those obtained by an established HPLC technique. No statistically significant differences being found between both methods.     

The Potentialities of Using a Graphite-Silicone Rubber Composite Electrode in the Determination of Propranolol

A graphite silicone-rubber composite electrode (GSR) was used for the determination of propranolol in drug formulation. Cyclic voltammetry (CV) at the GSR presented an irreversible oxidation peak at + 0.8 V vs. SCE, in Britton Robinson (B-R) buffer pH 7.4. The quantitative determination was carried out using differential pulse voltammetry (DPV). Under optimized parameters a linear dynamic range from 5.0 to 80.6 µ mol L^?1 with a detection limit of 1.1 µ mol L^?1 was observed. A repeatability of 4.5 ± 0.1 µA (n = 10) peak current was found after 10 successive DPV voltammograms of propranolol in the same solution after surface renovations. Using the proposed electrode, propranolol was quantified in a pharmaceutical formulation with results that agreed within 95% confidence level (t-test) with those from an official method.     

Highly Sensitive Differential Pulse and Square Wave Voltammetric Methods for Determination of Strontium Ranelate in Bulk and Pharmaceutical Dosage Form

The voltammetric behavior of Strontium Ranelate (SR) was studied using Cyclic (CV), differential pulse (DPV) and square wave (SWV) voltammetry. CV showed two well‐defined, irreversible, diffusion‐controlled anodic peaks using Britton‐Robinson buffer, pH 2.0 at Pencil graphite (PGE), Carbon paste (CPE) and glassy carbon (GCE) electrodes. The peak current‐concentration relationship was rectilinear over the range 1.0–10.0, 1.0–11.25 and 2.5–24.0 µg/mL at PGE, CPE and GCE respectively, with a minimum detectability of 0.17, 0.24 and 0.39 µg/mL for peak 1 and 0.19, 0.27 and 0.51 µg/mL for peak 2. Recoveries showed the high accuracy of the method; 99.8 %, 99.5 % and 99.7 % at PGE, CPE and GCE respectively for peak 1 and 100.1 %, 99.9 % and 99.7 % at PGE, CPE and GCE respectively for peak 2. Hence DPV and SWV were conducted for the quantitative determination of SR in its pure and pharmaceutical dosage form. the method was validated and the results were in good agreement with those obtained from the reported method.     

Fabrication of amperometric cholesterol biosensor based on SnO<Subscript>2</Subscript> nanoparticles and Nafion-modified carbon paste electrode

This study reports the fabrication of an amperometric cholesterol biosensor based on cholesterol oxidase (ChOx), SnO₂NPs and Nafion-modified carbon paste enzyme electrodes (CPE/SnO₂NPs-ChOx/Naf). The electrochemical characterisations of BCPE and CPE/SnO₂NPs were performed using CV and EIS. The determination of cholesterol was carried out by electrochemical oxidation of H₂O₂ at 0.6 V vs. Ag/AgCl. The CPE/SnO₂NPs-ChOx/Naf presented a linear range from 0.20 μ.mol L^?1 to 4.95 μmol L^?1 with a low limit of detection (0.04 μ.mol L^?1). In addition, the optimal values for pH and temperature were found to be 7.5 and 35°C, respectively. The CPE/SnO₂NPs-ChOx/Naf was used for the determination of cholesterol in serum samples and good results were obtained.     

Electrochemical Characterization and Rapid Voltammetric Determination of Riluzole in Pharmaceuticals and Human Serum

The electrochemical oxidation of riluzole was investigated using cyclic and linear sweep voltammetry. Under optimized conditions, current and concentration showed linear dependence in Britton Robinson buffer at pH 3.00 for boron doped diamond and pH 3.00 phosphate buffers for glassy carbon electrodes. Differential pulse and square wave voltammetry were used for the determination of riluzole levels in serum samples and pharmaceutical formulations. The limit of detections were found as 5.25 × 10^?7 M and 8.26 × 10^?8 M for glassy carbon electrode and 1.78 × 10^?7 M and 8.42 × 10^?8 M for boron-doped diamond electrodes, in serum samples, using differential pulse and square wave methods, respectively.