Voltammetric Determination of Dopamine in Human Serum and Urine at a Glassy Carbon Electrode Modified by Cysteic Acid Based on Electrochemical Oxidation of L ‐cysteine

Abstract

The voltammetric behavior of dopamine was studied at a glassy carbon electrode modified by cysteic acid, based on electrochemical oxidation of L ‐cysteine. The modified electrode showed strong electrocatalytic activity towards dopamine and good selectivity. In a phosphate buffer solution (pH 7.4), the anodic peak current obtain from the differential pulse voltammetry of dopamine was linearly dependent on its concentration in the range of 5×10^?9 to 4.0×10^?6mol · L^?1, with a detection limit of 2×10^?9mol · L^?1. The low‐cost modified electrode had been applied to the determination of dopamine in human serum and urine samples with satisfactory results.     

Synergistic Effect of Graphene and Multiwalled Carbon Nanotubes on a Glassy Carbon Electrode for Simultaneous Determination of Uric Acid and Dopamine in the Presence of Ascorbic Acid

A poly(diallyldimethylammonium chloride)-graphene-multiwalled carbon nanotube modified glassy carbon electrode was fabricated and evaluated by cyclic voltammetry and differential pulse voltammetry. The modified electrode offered high sensitivity, selectivity, excellent long-term stability, and electrocatalytic activity for uric acid and dopamine. This sensor showed wide linear dynamic ranges of 5.0 to 350.0 µmol L^?1 for uric acid and 10.0 to 400.0 µmol L^?1 for dopamine in the presence of 500 µmol L^?1 ascorbic acid. The limits of detection were 0.13 for uric acid and 0.55 µmol L^?1 for dopamine. This functionalized electrode has potential application in bioanalysis and biomedicine.     

Simultaneous Determination of Dopamine and Uric Acid by Electrocatalytic Oxidation on a Carbon Paste Electrode Using Pyrogallol Red as a Mediator

A sensitive and selective electrochemical method for the simultaneous determination of dopamine (DA) and uric acid (UA) was developed using a pyrogallol red modified carbon paste electrode. Under the optimized conditions, the peak current was linearly dependent on 1.0–700.0 μmol L^?1 DA and 50.0–1000.0 μmol L^?1 UA. The detection limits for DA and UA were 0.78 μmol L^?1 and 35 μmol L^?1, respectively. Finally, this method was also examined for the determination of DA and uric acid in real samples such as drugs and urine.     

Flow injection amperometric determination of hydrogen peroxide in household commercial products with a ruthenium oxide hexacyanoferrate modified electrode

Hydrogen peroxide was determined in oral antiseptic and bleach samples using a flow-injection system with amperometric detection. A glassy carbon electrode modified by electrochemical deposition of ruthenium oxide hexacyanoferrate was used as working electrode and a homemade Ag/AgCl (saturated KCl) electrode and a platinum wire were used as reference and counter electrodes, respectively. The electrocatalytic reduction process allowed the determination of hydrogen peroxide at 0.0 V. A linear relationship between the cathodic peak current and concentration of hydrogen peroxide was obtained in the range 10–5000 μmol L^?1 with detection and quantification limits of 1.7 (S/N?=?3) and 5.9 (S/N?=?10) μmol L^?1, respectively. The repeatability of the method was evaluated using a 500 μmol L^?1 hydrogen peroxide solution, the value obtained being 1.6% (n?=?14). A sampling rate of 112 samples h^?1 was achieved at optimised conditions. The method was employed for the quantification of hydrogen peroxide in two commercial samples and the results were in agreement with those obtained by using a recommended procedure.     

Carbon paste electrode modified with Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles and BMI.PF<Subscript>6</Subscript> ionic liquid for determination of estrone by square-wave voltammetry

A carbon paste electrode (CPE) modified with Fe₃O₄ nanoparticles (Fe₃O₄ NP) and the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (IL BMI.PF₆) was employed for the electroanalytical determination of estrone (E1) by square-wave voltammetry (SWV). At the modified electrode, cyclic voltammograms of E1 in B–R buffer (pH 12.0) showed an adsorption-controlled irreversible oxidation peak at around +0.365 V. The anodic current increased by a factor of five times and the peak potential shifted 65 mV to less positive values compared with the unmodified CPE. Under optimized conditions, the calibration curve obtained showed two linear ranges: from 4.0 to 9.0 μmol L^?1 and from 9.0 to 100.0 μmol L^?1. The limits of detection (LOD) and quantification (LOQ) attained were 0.47 and 4.0 μmol L^?1, respectively. The proposed modified electrode was applied to the determination of E1 in pork meat samples. Data provided by the proposed modified electrode were compared with data obtained by UV–vis spectroscopy. The outstanding performance of the electrochemical device indicates that Fe₃O₄ NP and the IL BMI.PF₆ are promising materials for the preparation of chemically modified electrodes for the determination of E1.     

Rapid voltammetric determination of maltol in some foods and beverages using a poly(methylene blue)/graphene-modified glassy carbon electrode

A novel poly(methylene blue)/graphene composite glassy carbon electrode was fabricated and the electrochemical behavior of maltol at the modified electrode was studied by cyclic voltammetry. In phosphate-buffered solution, the modified electrode exhibited excellent electrocatalytic activity towards the electrochemical oxidation of maltol. Under optimized conditions, the oxidation peak current showed a linear relationship with the concentrations of maltol in the ranges of 8.00?×?10^?7 to 4.00?×?10^?5 and 4.00?×?10^?5 to 5.40?×?10^?4 mol L^?1, with a detection limit of 6.50?×?10^?8 mol L^?1. The performance of the developed method was validated in terms of linearity (r?=?0.9981 and 0.9955), recovery (97.0?99.3 %), reproducibility (relative standard deviations?≤?3.1 %, n?=?6), and robustness. The method shows excellent sensitivity, selectivity, and reproducibility and has been successfully applied to analyzing maltol in a wide variety of food products.     

Fabrication of a nanostructured TiO2/carbon nanotube composite electrode for voltammetric and impedimetric determination of NTO explosive in the water and soil samples

An electrochemical oxidation route was developed for sensitive and selective assay of nitrotriazolone (NTO) explosive in some environmental samples on a multi-walled carbon nanotube (MWCNTs)/TiO₂ nanocomposite paste electrode, for prevention of the analytical interference of conventional reducible energetic compounds. Detailed evaluations were made for the electrochemical behaviour of NTO on the modified electrode by adsorptive stripping voltammetry, electrochemical impedance spectroscopy (EIS) and chronoamperometry techniques in the pH range of 2.0–10.0. Parameters such as diffusion coefficient constant of NTO were calculated, and various experimental conditions were also optimised. Under optimal conditions the calibration curve had two linear dynamic ranges of 130.0–3251.5 μg L^?1 and 6.5–26.0 mg L^?1 with a detection limit of 26.0 μg L^?1 (0.2 μmol L^?1) and precision of <3%. This electrochemical sensor was further applied to determine NTO in real soil and water samples with satisfactory results.     

Electrochemical oxidation behavior of 8-azaguanine at graphene-Nafion composite film-modified glassy carbon electrode

A simple but highly sensitive electrochemical sensor for the determination of 8-azaguanine based on graphene-Nafion nanocomposite film-modified glassy carbon electrode (G-Nafion/GCE) was reported. The electrochemical behaviors of 8-azaguanine at G-Nafion/GCE were investigated by cyclic voltammetry (CV), square wave voltammetry (SWV), chronoamperometry (CA), and chronocoulometry (CC). The results showed that the electrochemical sensor exhibited excellent electrocatalytic activity to 8-azaguanine. 8-Azaguanine can be effectively accumulated at G-Nafion/GCE and produce a sensitive anodic peak, due to the synergetic functions of graphene and Nafion. Under the selected conditions, the modified electrode in pH 1.98 Britton-Robinson buffer solution showed a linear voltammetric response to 8-azaguanine within the concentration range of 5.0 × 10^?8～3.0 × 10^?5 mol L^?1, with the detection limit of 1.0 × 10^?8 mol L^?1. And, the method was also applied to detect 8-azaguanine in spiked human urine with wonderful satisfactory results.     

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.     

Electrochemical sensor for detection of imipramine antidepressant at low potential based on oxidized carbon nanotubes,ferrocenecarboxylic acid,and cyclodextrin: application in psychotropic drugs and urine samples

Imipramine (IMP), a tricyclic antidepressant drug, is commonly prescribed for treatment of psychiatric patients suffering from different forms of depression. The appropriate amount of drug intake is crucial to ensure the optimum therapeutic effects minimizing severe collateral effects and toxicity. Therefore, the monitoring of imipramine is essential for its clinical applications. Herein, we report an electrochemical sensor based on a composite of ferrocenecarboxylic acid (FCA), β-cyclodextrin (CD), and oxidized multi-walled carbon nanotubes (f-CNT) modified glassy carbon electrode for detection of IMP at low potential. The electrochemical behavior of the proposed sensor was characterized by scanning electron microscopy, Raman spectroscopy, and cyclic voltammetry. The results show that imipramine determination using the proposed sensor occurs around 0 V vs Ag/AgCl in phosphate buffer pH 7.0. The calibration curves were obtained by cyclic voltammetry and differential pulse voltammetry, with linear ranges of 10 to 350 μmol L^?1 and 0.1 to 10 μmol L^?1, respectively. A detection limit of 0.03 μmol L^?1 was obtained for the detection of IMP. The sensor was applied for IMP determination in psychotropic drugs and urine samples and the results show a recovery percentage between 99 and 101% for the analyte.     

Detection of rutin at DNA modified carbon paste electrode based on a mixture of ionic liquid and paraffin oil as a binder

A DNA-modified carbon paste electrode (DNA-CPIE) was designed by using a mixture of the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate and paraffin oil as the binder. The electrochemistry of rutin at the DNA-CPIE was investigated by cyclic voltammetry and differential pulse voltammetry. Rutin exhibits a pair of reversible redox peaks in buffer solutions of pH 3.0, and respective electrochemical parameters are established. Under the optimal conditions, the oxidative peak current is linear with the concentration of rutin in the range from 8?×?10^?9 to 1?×?10^?5 mol L^?1, and the detection limit is 1.3?×?10^?9 mol L^?1 (at S/N?=?3). The electrode exhibits higher sensitivity compared to DNA modified carbon paste electrode without ionic liquid and better selectivity comparing with electrodes without DNA. It also showed good performance, stability, and therefore represents a viable method for the determination of rutin.     

Covalent grafting tyrosinase and its application in phenolic compounds detection

A stepwise strategy is reported for the design of a meditor-free amperometric tyrosinase biosensor. It is based on the azide-alkyne click reaction and carbodiimide coupling. Firstly, azide-terminated alkane thiols monolayers were self-assembled on the Au electrode surface. Then, nitrophenyl groups were covalent attached to the self-assembled monolayers (SAMs) via the click reaction of copper(I)-catalyzed 1,3-dipolar cycloadditions of azide-alkyne. Finally, the nitrophenyl group terminated SAMs were converted to aminophenyl-terminated interface by electrochemical reduction, and tyrosinase was covalent immobilized onto the Au electrode via carbodiimide reaction. Based on the stepwise strategy, a meditor-free amperometric tyrosinase biosensor was farbricated, and it showed good electrocatalytic reduction ability toward phenol, pyrocatechol and m-Cresol. Their linear ranges were over the range of 0.2 to 15.0 μmol·L^?1, 0.2 to 73.0 μmol·L^?1, and 0.2 to 33.0 μmol·L^?1, respectively.     

Evaluation of antioxidative capacity via measurement of the damage of DNA using an electrochemical biosensor and an ionic liquid solvent

We report on the electrodeposition of palladium nanomaterials in choline chloride–based ionic liquid ethaline. A glassy carbon electrode (GCE) was modified with cobalt nanoparticles (acting as sacrificial templates) and a GCE modified with palladium nanoparticles (PdNPs) were fabricated and used to study the electrocatalytic oxidation of hydrazine (N₂H₄). Scanning electron microscopy revealed that the PdNP modified GCE has a uniform morphology. Zero current potentiometry was used for in-situ probing the changes in interfacial potential of the oxidation of hydrazine. An amperometric study showed that the PdNP modified GCE possesses excellent electrocatalytic activity towards N₂H₄. The modified electrode displays a fast response (<2 s), high sensitivity (74.9 μA m(mol L^?1)^?1?cm^?2) and broad linearity in the range from 0.1 to 800 μmol L^?1 with a detection limit of 0.03 μmol L^?1 (S/N?=?3).

Highly sensitive electrocatalytic determination of pyrazinamide using a modified poly(glycine) glassy carbon electrode by square-wave voltammetry

A new voltammetric sensor based on electropolymerization of glycine at glassy carbon electrode (GCE) was developed and applied to determine of pyrazinamide (PZA) by square-wave voltammetry (SWV). The initial cyclic voltammetric studies showed an electrocatalytic activity of poly(Gly)/GCE on redox system of pyrazinamide in 0.1 mol L^?1 phosphate buffer solution pH 7.5, with E _Pc and E _Pa in ?0.85 and ?0.8 V (versus E _Ag/AgCl), respectively. Studies at different scan rates suggest that the redox system of pyrazinamide at poly(Gly)/GCE is a process controlled by diffusion in the interval from 10 to 100 mV s^?1. Square-wave voltammetry-optimized conditions showed a linear response of PZA concentrations in the range from 0.47 to 6.15 μmol L^?1 (R?=?0.998) with a limit of detection (LOD) of 0.035 μmol L^?1 and a limit of quantification (LOQ) of 0.12 μmol L^?1. The developed SWV-poly(Gly)/GCE method provided a good intra-day (RSD?=?3.75 %) and inter-day repeatability (RSD?=?4.96 %) at 4.06 μmol L^?1 PZA (n?=?10). No interference of matrix of real samples was observed in the voltammetric response of PZA, and the method was considered to be highly selective for the compound. In the accuracy test, the recovery was found in the range of 98.2 and 104.0 % for human urine samples and pharmaceutical formulation (tablets). The PZA quantification results in pharmaceutical tablets obtained by the proposed SWV-poly(Gly)/GCE method were comparable to those found by official analytical protocols.     

Electrocatalytic Oxidation of Formaldehyde on Copper Oxide Nano-crystalline Modified Glassy Carbon Electrode

This research found a cheap and efficient catalyst for electrooxidation of formaldehyde (HCHO). A CuO nano‐crystalline modified glassy carbon electrode (GCE) was fabricated and had an excellent electrocatalytic activity towards the oxidation of HCHO. Both the effect of potential scan rate and the effect of HCHO concentration on the electrocatalytic oxidation performance of the electrode were investigated. The amperometric current response of the electrode was proportional to HCHO concentration in the range of 1.0 µmol·L^?1–10.0 mmol·L^?1 with a detection limit (s/n=3) of 0.25 µmol·L^?1. The electrode was stable, showing the CuO nano‐crystlline is promising for applications in fuel cells and electrochemical sensors.     

Voltammetric Determination of Methylparaban in Cosmetics Using a Multi-Wall Carbon Nanotubes/Nafion Composite Modified Glassy Carbon Electrode

A novel voltammetric sensor using multi-wall carbon nanotubes (MWNTs) coupled with Nafion modified glassy carbon electrode (GCE) was developed for the detection of methylparaben (MP). The sensor exhibited good electrocatalytic activity toward the oxidation of MP in the phosphate buffer solution (PBS, pH 6.5). It displayed good sensitivity, repeatability, reproducibility, and long-term stability. Under the optimized conditions, the anodic peak current was linear with the concentration of MP in the range of 3 × 10^?6 mol L^?1 to 1 × 10^?4 mol L^?1. The detection limit was 1 × 10^?6 mol L^?1. The proposed method was successfully applied to determine MP in cosmetics with satisfactory results.     

Electrochemical sensor for heparin based on a poly(thionine) modified glassy carbon electrode

A poly(thionine) thin film modified electrode was successfully assembled on the surface of the glassy carbon electrode by means of electrochemical polymerization, which was carried out with cyclic voltammetric sweeping in the potential range 0 to +1.4 V (vs. Ag/AgCl) in perchloric acid solution containing 0.1 mmol L^?1 thionine. The film modified electrode exhibited a couple of well-defined redox peaks, and the redox peaks decreased correspondingly without a shift of the peak potential after the addition of heparin. The conditions of the binding reaction and the electrochemical detection were optimized. Under the optimum conditions the decrease of the peak current was proportional to the concentration of heparin in the range 4.0 to 22.0 μg mL^?1 and the detection limit was 0.28 μg mL^?1. The relative standard deviation (RSD) for five parallel determinations of 10.0 μg mL^?1 heparin was 0.93%. The effects of potentially interfering species were investigated and the method was successfully applied to the determination of heparin in a pharmaceutical formulation.     

Determination of Methimazole on a Multiwall Carbon Nanotube Titanium Dioxide Nanoparticle Paste Electrode

A multiwall carbon nanotube titanium dioxide nanoparticle modified carbon paste electrode was used for direct determination of methimazole. The nanoparticles in the carbon paste increased the surface area of the electrode and improved the sensitivity by enhancing the peak current. The electrochemical behavior of methimazole on the modified electrode was investigated. Experimental variables such as pH and electrode composition were optimized. At the optimum pH 7.0 (universal buffer), the modified electrode had a linear dynamic range of 0.5 to 100.0 μmol L^{? 1} (0.1–11.4 ppm) with a limit of detection of 0.17 μmol L^{? 1} . The application of the electrode for the determination of methimazole in pharmaceuticals and blood serum was investigated.     

Determination of allura red using composites of water-dispersible reduced graphene oxide-loaded Au nanoparticles based on ionic liquid

A facile route for producing reduced graphene oxide (RGO)-loaded Au nanoparticles based on ionic liquids (IL) has been proposed, in which the as-prepared RGO can be dispersed stably in water. With the assistance of IL, Au nanoparticles were uniformly and densely absorbed on the surfaces of the IL functionalised reduced graphene oxide (IRGO), forming a new composite of IRGO/Au with high dispersibility. This IRGO/Au composite enhanced its electrochemical signal obviously in the measurement of allura red in foods and exhibited a wider linear response ranging from 0.297 (0.0006 μmol L^?1) to 99.3 μg L^?1 (0.2 μmol L^?1) with lower detection limit of 0.213 μg L^?1 (0.00043 μmol L^?1) at a signal-to-noise ratio of 3. To further study the practical applicability of the proposed sensor, the modified electrode was successfully applied to detect allura red in five kinds of common foods and the assay results were in a good agreement with the reference values detected by HPLC.     

Sensitive detection of sulfanilamide by redox process electroanalysis of oxidation products formed in situ on glassy carbon electrode

This paper reported a simple method for sulfanilamide determination by redox process electroanalysis of oxidation products (SFDox) formed in situ on glassy carbon electrode. The CV experiments showed a reversible process after applied E _acc = + 1.06 V and t _acc = 1 s, in 0.1 mol L^?1 BRBS (pH = 2.0) at 50 mV s^?1. Different voltammetric scan rates (from 10 to 450 mV s^?1) suggested that the redox peaks of SFDox on the glassy carbon electrode (GCE) is an adsorption-controlled process. Square-wave voltammetry (SWV) method optimized conditions showed a linear response to SFD from 3.00 to 250.0 μmol L^?1 (R = 0.998) with a limit of detection of 0.638 μmol L^?1 and limit of quantification of 2.0 μmol L^?1. The developed the SWV method was successfully used in the determination of SFD pharmaceutical formulation and human serum. The SFD quantification results in pharmaceutical obtained by SWV-GCE were comparable to those found by official analytical protocols.