Study on Diffusion Mechanisms and Determination of Dihydroxybenzene Isomers at the Pre‐anodized Inlaying Ultrathin Carbon Paste Electrode

In this paper, nichrome was adopted as a substrate, to fabricate the pre‐anodized inlaying ultrathin carbon paste electrode (PAIUCPE). The electrochemical behaviors and diffusion mechanisms of three dihydroxybenzene isomers at the electrode were carefully investigated. The effect of pH on oxidation peak current was also detailedly explained. The results were shown that oxidation peak current not only related to the reaction of electroactive materials at the working electrode, but also depended on the reaction variable of reduction at the auxiliary electrode. The oxidation peaks of hydroquinone (HQ), catechol (CC) and resorcinol (RC) located at 0.181 V, 0.288 V and 0.736 V. For CC, RC and HQ, the oxidation peak currents were linear to the concentrations at the range of 5.0 × 10^?6～5.0 × 10^?4 mol/L, 3.0 × 10^?6～5.0 × 10^?4 mol/L and 4.0 × 10^?6～4.0 × 10^?4 mol/L with the detection limits of 2.0 × 10^?7 mol/L, 1.2 × 10^?7 mol/L and 1.2 × 10^?7 mol/L, respectively. The proposed method was successfully applied in the simultaneous determination of dihydroxybenzene isomers in artificial sewage samples with satisfactory results.     

Simple sensor for simultaneous determination of dihydroxybenzene isomers

A simple sensor based on bare carbon ionic liquid electrode was fabricated for simultaneous determination of dihydroxybenzene isomers in 0.1 mol L⁻¹ phosphate buffer solution (pH 6.0). The oxidation peak potential of hydroquinone was about 0.136 V, catechol was about 0.240 V, and resorcinol 0.632 V by differential pulse voltammetric measurements, which indicated that the dihydroxybenzene isomers could be separated absolutely. The sensor showed wide linear behaviors in the range of 5.0 × 10⁻⁷–2.0 × 10⁻⁴ mol L⁻¹ for hydroquinone and catechol, 3.5 × 10⁻⁶–1.535 × 10⁻⁴ mol L⁻¹ for resorcinol, respectively. And the detection limits of the three dihydroxybenzene isomers were 5.0 × 10⁻⁸, 2.0 × 10⁻⁷, 5.0 × 10⁻⁷ mol L⁻¹, respectively (S/N = 3). The proposed method could be applied to the determination of dihydroxybenzene isomers in artificial wastewater and the recovery was from 93.9% to 104.6%.     

Pt||ZrO2 nanoelectrode array synthesized through the sol–gel process: evaluation of their sensing capability

Homogeneous, circular Pt||ZrO₂ nanoelectrodes have been synthesized through the sol–gel chemistry and the dip-coating process. These nanoelectrode arrays have been evaluated as a platform for electropolymerization of phenol, as model. We have shown that the microstructure of the polymer depends on the confined environment of the electrode and on the position of the –OH group of the monomer. Additionally, these nanoelectrodes have been tested as an electrochemical sensor for dihydroxybenzene isomers in aqueous medium. These Pt||ZrO ₂ nanoelectrodes exhibit a detection limit of 2?×?10^?7?M for resorcinol and 1?×?10^?6?M for catechol.     

Simultaneous voltammetric determination of dihydroxybenzene isomers using a poly(acid chrome blue K)/carbon nanotube composite electrode

A novel modified electrode was fabricated by electropolymerization of acid chrome blue K at a multi-walled carbon nanotubes modified glassy carbon electrode. The electrode developed was used for simultaneous determination of the isomers of dihydroxybenzene in environmental samples using first order linear sweep derivative voltammetry with background subtraction. A linear relationship between peak current and concentration of hydroquinone, catechol and resorcinol was obtained in the range of 1 × 10⁻⁶–1 × 10⁻⁴ mol L⁻¹, and the detection limits were estimated to be 1 × 10⁻⁷, 1 × 10⁻⁷ and 9 × 10⁻⁸ mol L⁻¹, respectively. The constructed electrode showed excellent reproducibility and stability. Real water samples were analyzed and satisfactory results were obtained. This method provides a new way of constructing electrodes for environmental and biological analysis.     

Simultaneous Determination of Hydroquinone and Catechol at a Glassy Carbon Electrode Modified with Multiwall Carbon Nanotubes

A simply and high selectively electrochemical method for simultaneous determination of hydroquinone and catechol has been developed at a glassy carbon electrode modified with multiwall carbon nanotubes (MWNT). It was found that the oxidation peak separation of hydroquinone and catechol and the oxidation currents of hydroquinone and catechol greatly increase at MWNT modified electrode in 0.20 M acetate buffer solution (pH 4.5). The oxidation peaks of hydroquinone and catechol merge into a large peak of 302 mV (vs. Ag/AgCl, 3 M NaCl) at bare glassy carbon electrode. The two corresponding well‐defined oxidation peaks of hydroquinone in the presence of catechol at MWNT modified electrode occur at 264 mV and 162 mV, respectively. Under the optimized condition, the oxidation peak current of hydroquinone is linear over a range from 1.0×10^?6 M to 1.0×10^?4 M hydroquinone in the presence of 1.0×10^?4 M catechol with the detection limit of 7.5×10^?7 M and the oxidation peak current of catechol is linear over a range from 6.0×10^?7 M to 1.0×10^?4 M catechol in the presence of 1.0×10^?4 M hydroquinone with the detection limit of 2.0×10^?7 M. The proposed method has been applied to simultaneous determination of hydroquinone and catechol in a water sample with simplicity and high selectivity.     

Sensitive Electrochemical Determination of Catechol with a Graphene Modified Carbon Ionic Liquid Electrode

In this paper a graphene (GR) modified carbon ionic liquid electrode (CILE) was fabricated and used as the voltammetric sensor for the sensitive detection of catechol. Due to the specific physicochemical characteristics of GR such as high surface area, excellent conductivity and good electrochemical properties, the modified electrode exhibits rapid response and strong catalytic activity with high stability toward the electrochemical oxidation of catechol. A pair of well‐defined redox peaks appeared with the anodic and the cathodic peak potential located at 225 mV and 133 mV (vs.SCE) in pH 6.5 phosphate buffer solution, respectively. Electrochemical behaviors of catechol on the GR modified CILE were carefully investigated and the electrochemical parameters were calculated with the results of the electrode reaction standard rate constant (k_s) as 1.24 s^?1, the charge transfer coefficient (α) as 0.4 and the electron transfer number (n) as 2. Under the selected conditions the differential pulse voltammetric peak current increased linearly with the catechol concentrations in the range from 1.0 × 10^‐7 to 7.0 × 10^?4mol L‐1 with the detection limit as 3.0 × 10^?8mol L‐1 (3σ). The proposed method was further applied to the synthetic waste water samples determination with satisfactory results     

Simultaneous Voltammetry Determination of Dihydroxybenzene Isomers by Nanogold Modified Electrode

A convenient electrochemical deposition method to prepare nanogold/glassy carbon modified electrode (nano‐Au/GCE) is adopted. In 0.1 mol/L HAc‐NaAc buffer solution (pH 4.61), the nano‐Au/GCE shows an excellent electrocatalytical behavior for the redox of dihydroxybenzene. A simple, rapid and highly selective voltammetry for simultaneous determination of dihydroxybenzene isomers, hydroquinone, catechol, and resorcinol, is developed using the nano‐Au/GCE. This method has been applied to the direct determination of the three dihydroxybenzene isomers in artificial wastewater.     

Voltammetric Determination of 3‐Nitrofluoranthene and 3‐Aminofluoranthene at Boron Doped Diamond Thin‐Film Electrode

The voltammetric behavior of 3‐nitrofluoranthene and 3‐aminofluoranthene was investigated in mixed methanol‐water solutions by differential pulse voltammetry (DPV) at boron doped diamond thin‐film electrode (BDDE). Optimum conditions have been found for determination of 3‐nitrofluoranthene in the concentration range of 2×10^?8–1×10^?6 mol L^?1, and for determination 3‐aminofluorathnene in the concentration range of 2×10^?7–1×10^?5 mol L^?1, respectively. Limits of determination were 3×10^?8 mol L^?1 (3‐nitrofluoranthene) and 2×10^?7 mol L^?1 (3‐aminofluoranthene).     

Electroanalytical Method for Determining Pyrogallol in Biodiesel in the Presence of a Surfactant

A sensitive, straightforward electroanalytical method for determining pyrogallol (PY) in biodiesel in the presence of a surfactant was developed using a voltammetric technique and screen‐printed electrodes. The influence of surfactant addition (sodium dodecyl sulfate (SDS), Triton X‐100 (TX‐100), cetyltrimethylammonium bromide (CTAB), tetrabutylammonium iodide (TBAI), tetrabutylammonium bromide (TBAB), or tetraethylammonium bromide (TEAB)) on the supporting electrolyte (0.04 mol L^?1 Britton? Robinson buffer) was evaluated. Only CTAB significantly increased the oxidation peak current. Under optimal conditions, the method demonstrated linearity over the concentration range of 0.8–9.0×10^?6 mol L^?1, with limits of detection and quantification of 4.9×10^?7 and 1.5×10^?6 mol L^?1, respectively. The results were satisfactory, relative to those obtained using high‐performance liquid chromatography (HPLC).     

A Bipotentiostat Based 4‐Electrode Detection System for HPLC Analysis

With the assist of a microcomputer interfacing, a bipotentiostat in corporated 4‐electrode detection system was developed as a versatile electrochemical detector for HPLC. An amperometric chromatogram and two three‐dimensional chromatovoltammograms characterizing the electrochemical characteristics of analytes can be obtained in a single chromatographic run. By following the three operation modes developed, both the oxidizable and reducible analytes contained in sample solutions can be determined. The analytical capability of the 4‐electrode detection system was demonstrated by the analysis of solutions containing hydroquinone, catechol and ascorbic acid. From the calibration graphs obtained, linear coefficients better than 0.9992 were found for hydroquinone and catechol in a concentration range of 1.0 × 10^?4 to 1.0 × 10^?7 M, and a linear coefficient of 0.9929 was found for ascorbic acid in a concentration range of 1.0 × 10^?4 to 1.0 × 10^?6 M. The detection limits (based on S/N = 3) found were about 1.0 × 10^?7 M for hydroquinone and catechol and was 1.0 × 10^?6 M for ascorbic acid.     

Determination of α‐Lipoic acid on a Pyrolytic Graphite Electrode Modified with Cobalt Phthalocyanine

In this work voltammetric techniques were explored for quantification of α‐Lipoic acid (ALA) using a pyrolytic graphite electrode modified with cobalt phthalocyanine. Cyclic voltammograms recorded in phosphate buffer solution containing 1×10^?3 mol L^?1 of ALA presented an oxidation peak located at +0.8 V vs. SCE. The modification of the electrode produced a 100 mV shift of the onset oxidation potential to less positive value and a substantial increase in the ALA oxidation current. Among the voltammetric techniques explored, differential pulse voltammetry showed the best performance for quantifications of the analyte in low concentrations. Limits of detection and quantification of ALA obtained corresponds to 3.4×10^?9 mol L^?1 and 1.2×10^?8 mol L^?1, respectively.     

Electrocatalytic Oxidation of Catechol at Multi‐Walled Carbon Nanotubes Modified Electrode

In 0.05 mol/L phosphate buffer solution (pH 7.0), carbon nanotubes modified electrode exhibits rapid response, strong catalytic activity with high stability toward the electrochemical oxidation of catechol. The electrochemical behavior of catechol on both the multi‐walled and single‐walled carbon nanotubes modified electrode was investigated. The experimental conditions, such as pH of the solution and scan rate were optimized. The currents (measured by constant potential amperometry) increase linearly with the concentrations of catechol in the range of 2.0×10^?5–1.2×10^?3 mol/L. Moreover, at the multi‐walled carbon nanotubes modified electrode the electrochemical responses of catechol and ascorbic acid can be separated clearly.     

A Cerium Hexacyanoferrate (III) Nanoparticle‐modified Carbon Paste Electrode: Voltammetric Characterization and Behavior in the Presence of Dopamine

This study describes a fast and simple methodology for the preparation of Cerium (III) Hexacyanoferrate (II) (CeHCF) nanoparticles (NPs). The NPs were characterized by fourier transform infrared (FTIR), x‐ray diffraction (XRD), scanning electron microscopy (SEM) and cyclic voltammetry (CV). The CeHCF cyclic voltammogram indicate a well‐defined redox pair assigned as Fe²⁺/Fe³⁺ in the presence of cerium (III), with a formal potential of E^θ′=0.29 V (v=100 mV s^?1, KNO₃; 1.0 mol/L, pH 7.0). The carbon paste electrode modified with CeHCF (CeHCF‐CPE) was applied to the catalytic electrooxidation of dopamine applying Differential Pulse Voltammetry (DPV). DPV showed linear response at two concentration ranges, from 9.0×10^?7 to 8.0×10^?6 and 9.0×10^?6 to 1.0×10^?4 mol/L, with an LOD of 1.9×10^?7 and 1.0×10^?5 mol/L, respectively. The CeHCF‐CPE exhibited selectivity against substances commonly found in biological samples, with redox potentials close to that of dopamine, such as urea and ascorbic acid (AA). Subsequently the CeHCF‐CPE was successfully applied to the detection of dopamine in simulated urine samples, with recovery percentages ranging between 99 and 103%.     

Direct Simultaneous Determination of α‐ and β‐Naphthol Isomers at GC‐Electrode Modified with CNTs Network Joined by Pt Nanoparticles Through Derivative Voltammetry

The semi‐derivative technique was adopted to improve the resolution and surfactant was added to sample solution to enhance the sensitivity, α‐ and β‐naphthol isomers could be determined directly and simultaneously at glassy carbon electrode modified with carbon nanotubes network joined by Pt nanoparticles. In 0.1 mol L^?1 HAc‐NaAc buffer solution (pH 5.8), the linear calibration ranges were 1.0×10^?6 to 8.0×10^?4 mol L^?1 for both α‐ and β‐naphthols, with detection limits of 5.0×10^?7 for α‐ and 6.0×10^?7 mol L^?1 for β‐naphthol. The amount of naphthol isomers in artificial wastewater has been tested with above method, and the recovery was from 98% to 103%.     

Chemical Speciation of Antimony(III and V) in Water by Adsorptive Cathodic Stripping Voltammetry Using the 4‐(2‐Thiazolylazo) – Resorcinol

A simple adsorptive cathodic stripping voltammetry method has been developed for antimony (III and V) speciation using 4‐(2‐thiazolylazo) – resorcinol (TAR). The methodology involves controlled preconcentration at pH 5, during which antimony(III) – TAR complex is adsorbed onto a hanging mercury drop electrode followed by measuring the cathodic peak current (I_p,c) at ?0.39 V versus Ag/AgCl electrode. The plot of I_p,c versus antimony(III) concentration was linear in the range 1.35×10^?9–9.53×10^?8 mol L^?1.The LOD and LOQ for Sb(III) were found 4.06×10^?10 and 1.35×10^?9 mol L^?1, respectively. Antimony(V) species after reduction to antimony(III) with Na₂SO₃ were also determined. Analysis of antimony in environment water samples was applied satisfactorily.     

Simultaneous determination of dihydroxybenzene isomers utilizing a thiadiazole film electrode

The present study reports a sensitive electro-analytical method for the simultaneous determination of dihydroxybenzene isomers by using a thiadiazole film electrode, which was readily prepared by electropolymerization of 2,5-dimercapto-1,3,4-thiadiazole on a glassy carbon electrode with cyclic voltammetry. The functionalized electrode has a distinguishable and sensitive response to dihydroxybenzene isomers. Under the optimized conditions, the linear stripping peak currents showed good linear relationships with hydroquinone, catechol and resorcinol at concentration ranges 0.50-120, 0.50-110 and 1.00-110 μmol/L, and the detection limits are 0.1, 0.1 and 0.3 μmol/L, respectively. The proposed method is applicable to the simultaneous determination of dihydroxybenzene isomers in real samples with the relative standard deviations of less than 5.7% and the recovery rates of 95.6%-106%. The constructed electrode is characterized by simple preparation, good selectivity, and high sensitivity advantages.     

Simultaneous Determination of Dihydroxybenzene Isomers Using Preanodized Inlaying Ultrathin Carbon Paste Electrode

In this paper, we described a rapid, sensitive and selective method for simultaneous voltammetric determination of dihydroxybenzene isomers with a preanodized inlaying ultrathin carbon paste electrode (PAIUCPE). Scanning electron microscope (SEM), electrochemical impedance spectroscopy (EIS) and voltammetry were employed to characterize the configuration and electrochemical properties of the electrode. The resulting PAIUCPE exhibited excellent recognition ability towards dihydroxybenzene isomers. Three well‐defined oxidation peaks of catechol (CC), resorcinol (RC) and hydroquinone (HQ) can be identified entirely at the electrode. The oxidation peak potential difference between HQ and CC was 120 mV, CC and RC 430 mV, respectively. The peak currents increased linearly with increasing the concentration of dihydroxybenzene isomers. The proposed electrode can be applied to simultaneous determination of dihydroxybenzene isomers without previous chemical or physical separations.     

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.     

Study on the Electrochemical Behavior of Dopamine and Uric Acid at a 2‐Amino‐5‐mercapto‐[1,3,4] Triazole Self‐Assembled Monolayers Electrode

Selected from a series of structurally related heteroaromatic thiols, a newly synthesized reagent 2‐amino‐5‐mercapto‐[1,3,4] triazole (MATZ) was used to fabricate self‐assembled monolayers (SAMs) on gold electrode for the first time. The MATZ/Au SAMs was characterized by electrochemical methods and scanning electronic microscopy (SEM). In 0.04 mol/L Britton–Robinson buffer solution (pH 5), the electrochemical behavior of dopamine showed a quasireversible process at the MATZ/Au SAMs with an electrode kinetic constant 0.1049 cm/s. However, the electrochemical reaction of uric acid at the SAMs electrode showed an irreversible oxidation process, the charge‐transfer kinetics of uric acid was promoted by the SAMs. By Osteryoung square‐wave voltammetry (OSWV), the simultaneous determination of dopamine and uric acid can be accomplished with an oxidation peak separation of 0.24 V, the peak current of dopamine and uric acid were linearly to its concentration in the range of 2.5×10^?6–5.0×10^?4 mol/L for dopamine and 1×10^?6–1×10^?4 mol/L for uric acid with a detection limit of 8.0×10^?7 mol/L for dopamine and 7.0×10^?7 mol/L for uric acid. The MATZ/Au SAMs electrode was used to detect the content of uric acid in real urine and serum sample with satisfactory results.     

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.