A novel hydrazine electrochemical sensor based on the high specific surface area graphene

An ultrasensitive platform is presented for the determination of hydrazine by combining the high specific surface area and higher electrical conductivity of poly(sodium styrenesulfonate) (PSS) graphene nanocomposite film with amperometric detection. The PSS-graphene were synthesized by the Hummers method and used to modify a glassy carbon electrode. The material was characterized by scanning electron microscopy and is found to be suitable for sensing hydrazine. The overpotential of hydrazine on the modified electrode is 0.31 V which is lower than in many electrochemical sensors. The calibration curve for hydrazine is linear in the range from 3.0 to 300 µmol L^?1, and the detection limit is as low as 1 µmol L^?1. This is the first report in which such a high sensitivity and low limit of detection has been achieved. It is concluded that PSS graphene represents an efficient electron mediator for sensing hydrazine.     

Amperometric determination of the insecticide fipronil using batch injection analysis: comparison between unmodified and carbon-nanotube-modified electrodes

The electrochemical oxidation of fipronil is investigated on unmodified and multi-walled carbon-nanotube (MWCNT)-modified glassy carbon electrodes (GCEs), and its amperometric determination using batch injection analysis (BIA) is demonstrated. An oxidation peak was observed at 1.5 V in a 0.1 mol L^?1 HClO₄/acetone solution (50:50, v/v) on both surfaces. Although MWCNT-modified GCE provided greater sensitivity, the unmodified GCE showed low RSD value, wider linear range, and reduced adsorption of fipronil or its oxidized products on the electrode surface. A detection limit of 4.7 μmol L^?1 and linear range of 25–300 μmol L^?1 were obtained using a bare GCE. The method was applied in veterinary formulations with results in agreement with those obtained by high-performance liquid chromatography.     

Comparison of HPLC Methods for the Determination of Amino Sugars in Soil Hydrolysates

A study on the suitability of chromatographic techniques such as high performance anion exchange chromatography (HPAEC) with fluorescence detection (FL) and pulsed amperometric detection (PAD) and reversed phase (RP) chromatography for the determination of galactosamine, glucosamine, mannosamine, and muramic acid in soil hydrolysates was carried out. The reversed phase fluorescence method was rapid, provided good validation parameters, and employed relatively inexpensive instrumentation. The HPAEC methods had slightly higher limits of quantification, 0.6–5.0 µmol L^?1 (HPAEC-FL) and 1.0–10.0 µmol L^?1 (HPAEC-PAD), compared to the reversed phase fluorescence method (0.5–5.0 µmol L^?1). Various sample pretreatment methods and chromatographic methods were investigated and the advantages and disadvantages of the HPLC methods are discussed.     

Surfactant-intercalated smectite modified electrode: sensitive electrochemical detection of methyl orange dye

This work describes the use of organosmectite modified electrode to evaluate the electrochemical behaviour and to develop an electroanalytical procedure for the determination of methyl orange (MO) dye in natural water. Organosmectites were prepared by intercalation of hexadecyltrimethylammonium cations at various ratios into the interlayer of smectite. The synthesised organosmectites were characterised by various physicochemical techniques such as Fourier transform infrared spectroscopy, X-ray diffraction, field emission scanning electron microscopy and transmission electron microscopy. An amperometric sensor based on organosmectite as electrode modifier for MO sensing purposes was then evaluated by means of clay-film modified electrode using square wave voltammetry (SWV). The electrochemical procedure for MO analysis by stripping voltammetry involves two successive steps: accumulation of MO at open circuit conditions followed by a voltammetric detection in a same medium by the SWV technique. The peak current obtained (after 5 min preconcentration of 15 µmol L^?1 MO solution) on a glassy carbon electrode coated by a thin film of the modified clay was more than 2.5 times higher than that exhibited by the same substrate covered by a film of the pristine clay. Under optimised conditions, a linear calibration curve for MO was obtained in the concentration range from 0.1 to 1.6 µmol L^?1, leading to a detection limit of 4 × 10^?8 mol L^?1 (signal-to-noise ratio equal to 3). The interfering effect of various inorganic and organic ions likely to influence the stripping determination of the MO was also examined. To further validate application of this sensor, the proposed method was successfully used to the determination of MO in natural water with satisfactory results.     

The Use of Boron‐Doped Diamond Electrodes for the Amperometric Determination of Flavonoids in a Flow Injection System

Abstract

This paper describes the use of boron‐doped diamond electrode for the amperometric detection and quantification of flavonoids in tea samples using a flow injection system. Flavonoids are phenol derivates widely distributed in fruits, nuts, seeds, flowers, vegetable peels, and beverages; they are known to exhibit high antioxidative activities. After optimization, the experiments were performed at a fixed potential of 0.42 V vs Ag/AgCl with a flow rate of 2.5 ml min^?1 in a Britton‐Robinson buffer at pH 5.0. The results revealed that the peak current increases linearly with rutin concentration in the interval 0.1–2.5×10^?4 mol L^?1 and the detection limit was 7.7×10^?6 mol L^?1. The method was used for the determination of rutin in three different green tea (Camellia sinensis) infusions by the direct addition of 150 µL of untreated sample. The repeatability of current responses for injections of 150 µL rutin was evaluated to be 2.1% (n=20) and the analytical frequency was 100 Hz h^?1. The results were compared with the results obtained by high‐performance liquid chromatrography‐diode ray detector.     

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.     

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.     

Simultaneous Analysis of Sugars and Polyphenols in Tobacco by CZE with Amperometric Detection Based on a Cu2O/MWCNT-COOH Composite Electrode

A composite electrode was fabricated from Cu₂O powder, carboxyl-functionalized multi-wall carbon nanotubes (MWCNT-COOH), and paraffin oil in the proportions 51:17:32 (w/w). This composite electrode was used for amperometric detection (CZE–AD) in simultaneous capillary zone electrophoretic analysis of chlorogenic acid, rutin, sucrose, glucose, mannose, and fructose in tobacco samples. Under the optimum conditions, the six analytes could be separated in 100 mmol L^?1 NaOH buffer within 30 min. Good linearity was achieved in the range 1 × 10^?7–1 × 10^?4 mol L^?1 for the two polyphenols and 5 × 10^?6–1 × 10^?3 mol L^?1 for the four sugars. The detection limits (S/N = 3) for the polyphenols and sugars were as low as 10^?8 mol L^?1 and 10^?6 mol L^?1, respectively.     

Determination of prazosin in pharmaceutical samples by flow injection analysis with multiple-pulse amperometric detection using boron-doped diamond electrode

This work describes the development of a simple, fast and low-cost method for determining prazosin (PRA) in pharmaceutical samples by flow injection analysis with multiple-pulse amperometric (FIA-MPA) detection using a boron-doped diamond film electrode. Electrochemical detection of PRA was optimized in phosphate buffer pH 4.0 by cyclic voltammetry, in which PRA presented two oxidation processes around at 0.97 and 1.40 V versus Ag/AgCl (3.0 mol L^?1 KCl). In these conditions, PRA also showed one reduction process at ?0.75 V that is dependent on the oxidation processes. Thus, the determination of PRA by FIA-MPA detection consisted on the application of a two-potential waveform, E ₁ (generator potential)?=?1.6 V/400 ms and E ₂ (collector potential)?=??1.0 V/30 ms, with sample loop of 150 μL and flow rate of 3.0 mL min^?1. The method showed good repeatability (RSD?<?3.0 %) and high analytical frequency (70 injections per h). The working linear range was obtained from 2 to 200 μmol L^?1 with a limit of detection of 0.5 μmol L^?1. The recovery tests in all samples were approximately 100 %, and the results were compared with chromatographic methods.     

Simultaneous Electrochemical Determination of Hydroquinone and Catechol at MWNTs and Cobalt(II) Tetrakisphenylporphyrin Modified Electrode

A multi-wall carbon nanotubes (MWNTs) and cobalt(II) tetrakisphenylporphyrin (Co(II)TPP) modified glassy carbon electrode (MWNTs/Co(II)TPP/GCE) has been prepared. It can be used for individual or simultaneous determination of hydroquinone (HQ) and catechol (CC). The anodic peaks of HQ and CC can be separated well. Owing to the unique properties of MWNTs and special synergistic effect of MWNTs and Co(II)TPP, the modified electrode exhibited a remarkable and stable current response for CC and HQ. The linear ranges for CC and HQ were 1.0–450.0 µmol L^?1 and 0.8–400.0 µmol L^?1 with detection limits of 0.8 µmol L^?1 and 0.5 µmol L^?1, respectively. Furthermore, Co(II)TPP, MWNTs, and Co(II)TPP/MWNTs composite were also used to construct modified electrodes and the electrochemical performances were studied.     

Amperometric Nitric Oxide Sensor Based on Poly(Thionine)/Nafion‐Modified Electrode and Its Application in Monitoring Nitric Oxide Release from Rat Kidney

Abstract

A novel amperometric nitric oxide (NO) sensor based on a glassy carbon electrode modified with thionine and Nafion films has been developed. The oxidation peak current of NO increased significantly at the poly(thionine)/Nafion‐modified glassy carbon electrode (GCE), which can be used for the detection of NO. The oxidation peak current was linear with the concentration of nitric oxide over the range from 3.6×10^?7 to 6.8×10^?5 mol · L^?1, and the detection limit was 7.2×10^?8 mol · L^?1. This nitric oxide sensor showed high selectivity to nitric oxide determination, and some potential interference could be eliminated effectively. The nitric oxide sensor has been applied to monitor NO release from rat kidney stimulated by L‐arginine. The results indicated the applicability of the NO sensor to biomedical samples.     

Determination of Sudan I Using Electrochemically Reduced Graphene Oxide

Electrochemically reduced graphene oxide (ER-GO) was prepared by reducing exfoliated graphene oxide sheets on a glassy carbon electrode (GCE). The voltammetric responses of Sudan I-IV were studied at the ER-GO modified GCE (ER-GO/GCE). Compared with chemically reduced graphene oxide (CR-GO) modified electrode (CR-GO/GCE), ER-GO/GCE showed higher voltammetric responses to Sudan I. The electrode had a linear response to Sudan I in the range of 0.04–8.0 µmol L^?1 and a detection limit of 0.01 µmol L^?1. The real sample determination indicated that the proposed method was reliable, effective, and sufficient.     

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.     

Self-assembled sensor based on boron-doped diamond and its application in voltammetric analysis of picloram

A self-assembled sensor based on a boron-doped diamond was investigated as a sensitive tool for voltammetric analysis of a member of a pyridine herbicide family - picloram. A cyclic voltammetry and a differential pulse voltammetry were applied for investigation of the voltammetric behaviour and quantification of this herbicide. Picloram yielded one well-developed irreversible oxidation signal at a very positive potential about +1.5 V vs. Ag/AgCl/3 mol L^?1 KCl electrode in an acidic medium and 1 mol L^?1 H₂SO₄ was chosen as a suitable supporting electrolyte. Operating parameters of differential pulse voltammetry were optimized and the proposed voltammetric method provided a high repeatability (a relative standard deviation of 20 repeated measurements at a concentration level of picloram of 50 µmol L^?1 equaled to 2.58%), a linear concentration range from 2.5 to 90.9 µmol L^?1 and a low limit of detection (LD = 1.64 µmol L^?1). Practical usefulness of the ‘environmentally-green’ electrochemical sensor was verified by an analysis of spiked water samples with satisfactory recoveries.     

Chemiluminescent Determination of Vitamin B12 Using Charge Coupled Device (CCD)

A method was developed for the determination of vitamin B₁₂ based on the enhancement of cobalt (II) on the chemiluminescence (CL) reaction between luminol and percarbonate (powerful source of hydrogen peroxide). The release of cobalt (II) from the vitamin B₁₂ was reached by a simple and fast microwave digestion (20 s microwave digestion time and a mix of nitric acid and hydrogen peroxide). A charge coupled device (CCD) photodetector, directly connected to the cell, coupled with a simple continuous flow system was used to obtain the full spectral characteristics of cobalt (II) catalyzed luminol-percarbonate reaction.

The optima experimental conditions were established: 8.0 m mol L^?1 luminol in a 0.075 mol L^?1 carbonate buffer (pH 10.0) and 0.15 mol L^?1 sodium percarbonate, in addition to others experimental parameters as 0.33 mL s^?1 flow rate and 2 s integration time, were the experimental conditions which proportionate the optimum CL emission intensity. The emission data were best fitted with a second-order calibration graph over the cobalt (II) concentration range from 4.00 to 300 µ g L^?1 (r² = 0.9990), with a detection limit of 0.42 µ g L^?1. The proposed method was successfully applied to the determination of vitamin B₁₂ in pharmaceuticals.     

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.     

Glucose biosensor based on graphite electrodes modified with glucose oxidase and colloidal gold nanoparticles

The electrochemistry of glucose oxidase (GOx) immobilized on a graphite rod electrode modified by gold nanoparticles (Au-NPs) was studied. Two types of amperometric glucose sensors based on GOx immobilized and Au-NPs modified working electrode (Au-NPs/GOx/graphite and GOx/Au-NPs/graphite) were designed and tested in the presence and the absence of N-methylphenazonium methyl sulphate in different buffers. Results were compared to those obtained with similar electrodes not containing Au-NPs (GOx/graphite). This study shows that the application of Au-NPs increases the rate of mediated electron transfer. Major analytical characteristics of the amperometric biosensor based on GOx and 13 nm diameter Au-NPs were determined. The analytical signal was linearly related to glucose concentration in the range from 0.1 to 10 mmol L^?1. The detection limit for glucose was found within 0.1 mmol L^?1 and 0.08 mmol L^?1 and the relative standard deviation in the range of 0.1–100 mol L^?1 was 0.04–0.39%. The τ_1/2 of V _max characterizes the storage stability of sensors: this parameter for the developed GOx/graphite electrode was 49.3 days and for GOx/Au-NPs/graphite electrode was 19.5 days. The sensor might be suitable for determination of glucose in beverages and/or in food.     

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.     

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.     

Selenium-coated carbon electrode for anodic stripping voltammetric determination of copper(II)

We describe a new and promising type of selenium film electrode for anodic stripping voltammetry. This method is based on formation of copper selenide onto an in-situ formed selenium-film carbon electrode, this followed by Osteryoung square-wave anodic stripping voltammetry. Copper(II) is also in-situ electroplated in a test solution containing 0.01 mol L^-1 hydrochloric acid, 0.05 mol L^?1 potassium chloride and 500 µg L^?1 Se(IV) at a deposition potential of ?300 mV. The well-defined anodic peak current observed at about 200 mV is directly proportional to the Cu(II) concentration over the range from 1.0 to 100 µg L^?1 under the optimized conditions. The detection limit (three sigma level) is 0.2 µg L^?1 Cu(II) at 180 s deposition time. Relatively less interferences are shown from most of metal ions except for antimony(III). The method can be applied to analyses of river water and oyster tissue with good accuracy.