Voltammetric Study and Detection of Methane on Nickel Hydroxide–Modified Nickel Electrode

Abstract

The nickel hydroxide–modified nickel (NMN) electrode was prepared by cyclic voltammetry. The modified electrode exhibited better catalytic effect toward electrochemical oxidation of methane in 1.0 mol · L^?1 NaOH solution. The catalytic activation of nickel hydroxide on the nickel electrode surface was investigated in different supporting electrolyte solutions by the cyclic voltammetry method in detail, and the related electrochemical oxidation of methane at the NMN electrode was first proposed by amperometric i‐t curve method under the experiment conditions. The results indicated that in the 1.0 mol · L^?1 NaOH solution, the anodic peak current increased with the increased concentration of methane.     

An electrochemical sensor for p-aminophenol based on the mesoporous silica modified carbon paste electrode

A mesoporous silica was synthesised and used to modify the surface of carbon paste electrode (CPE). The electrochemical behaviours of p-aminophenol were investigated. Compared to the unmodified CPE, the mesoporous silica-modified CPE obviously lowers the oxidation potential of p-aminophenol, and remarkably increases its oxidation peak current. The effects of pH value, amount of mesoporous silica, accumulation potential and time were examined. As a result, a sensitive, rapid and convenient electroanalytical method was developed for p-aminophenol. The linear range is from 0.025?mg?L^?1 to 3?mg?L^?1, and the limit of detection is 0.01?mg?L^?1 after 2-min accumulation. Finally, the method was successfully used to determine p-aminophenol in water samples.     

Determination of Sulfite in Hair Waving Products Using Oxygen‐Incorporated Gold‐Modified Screen‐Printed Electrodes

An electrodeposition oxygen‐incorporated gold‐modified screen‐printed carbon electrode (AuOSPE) was fabricated to determine the sulfite content in hair waving products. The AuOSPE showed an electrocatalytic current for sulfite at +0.4 V (vs. Ag/AgCl). Compared with a gold screen‐printed electrode (AuSPE), the AuOSPE showed a higher electrocatalytic current. The increase in the electrocatalytic current was ascribed to the increase of the oxygen incorporated with gold atom on AuOSPE. The AuOSPE coupled with a flow injection analysis (FIA) system showed excellent oxidation current for sulfite in a 0.1 mol L^?1 phosphate buffer solution (PBS), pH 6.0. The linear working range for determining the sulfite content was 0.05 to 1200 mg L^?1 (0.625 µmol L^?1 to 15.00 mmol L^?1) with a calculated detection limit of 0.03 mg L^?1 (0.375 µmol L^?1) (DL, S/N=3). Relative standard deviations (RSD) of 3.03 %, 2.30 % and 4.26 % were calculated for consecutive injections (n=12) of 20, 300 and 900 mg L^?1 sulfite, respectively. The amount of sulfite in two hair waving products was determined by the proposed method and a standard iodometric method. The recoveries ranged from 96.18 % to 105.61 %. The AuOSPE showed high sensitivity, selectivity, stability and reproducibility for sulfite.     

Electrochemical determination of carbaryl oxidation in natural water and soil samples

An electrochemical method for the determination of carbaryl, after prior oxidation to 1,4-naphthoquinone in natural water and soils is reported. The coulometric oxidation of carbaryl at a platinum electrode was studied using 0.024 mol/L Britton-Robinson buffer (pH 7.0). The reduction of the oxidation product 1,4-naphthoquinone at a dropping mercury electrode was used for the indirect determination of carbaryl after separation on C₁₈ Sep-pak cartridges by differential pulse polarography (detection limits: 0.41 mg L^?1 of water and 0.47 mg kg^?1 of soil) and directly without separation by adsorptive stripping voltammetry (detection limits: 5 μg L^?1 of water and 7 μg kg^?1 of soil, for 75 s preconcentration time). Relative errors were lower than 3.7% and relative standard deviations smaller than 4.5%.     

Catalytic systems based on the organic nickel(ii) complexes in chronoamperometric determination of urea and creatinine

The organic nickel(ii) complexes with catalytic activity in the electrochemical oxidation of creatinine and urea were synthesized and studied. The signals of electrocatalytic oxidation of the studied carbonyl-containing amines in model solutions were obtained. The detection limit (by the 3σ-criterion) is 8.7·10^?6 and 2.7·10^?5 mol L^?1 for urea and creatinine, respectively.     

Simultaneous voltammetric determination of carbendazim and carbaryl in medicinal plant infusions with a boron-doped diamond electrode

This study is aimed to develop an electroanalytical methodology using a boron-doped diamond electrode to determine simultaneously and selectively carbendazim (CBZ) and carbaryl (CAR). In previous studies using cyclic voltammetry oxidation, peaks were observed at 1.03 V (CBZ) and 1.44 V (CAR), with characteristics of an irreversible process controlled by diffusion of species, with a supporting electrolyte of BR buffer (0.1 mol L^?1) and pH adjusted to 6.0. The differences between the potentials for both pesticides, about 400 mV, indicate the possibility of selective determination of CBZ and CAR. The square-wave voltammetric parameters were optimised. The best separation conditions were pH 6.0, square-wave frequency of 100 s^?1, pulse amplitude of 50 mV and scan increment of 2.0 mV. These parameters were used to obtain the calibration curves of CBZ and CAR. An analytical curve was constructed in the range concentration of CBZ of 1.3 mg L^?1 to 15.3 mg L^?1 and CAR of 1.0 mg L^?1 to 11.4 mg L^?1, respectively. The limits of detection (LOD) and limits of quantification (LOQ) for CBZ were 0.40 mg L^?1 and 1.30 mg L^?1, respectively. For CAR, the LOD and LOQ were 0.30 mg L^?1 and 1.00 mg L^?1, respectively. Sensitivity values were 0.78 and 2.60 µA/mg L^?1 for CBZ and CAR, respectively. The electroanalytical method was applied in Mikania glomerata infusions. The recovery values were 106.2% and 116.5% for CBZ and CAR, respectively. The results show that the developed method is suitable for application in medicinal plant samples.     

Determination of cadmium, chromium and copper in high salt samples by LA-ICP-OES after electrodeposition—preliminary study

A novel method is presented for determination of heavy metal ions in a high-saline matrix. It is based on the electrodeposition of the ions and subsequent laser ablation coupled to inductively coupled plasma optical emission spectrometry (LA-ICP-OES). Three arrangements for electrodeposition were worked out, two of them with stationary working electrodes. Materials for use in the working electrodes, and conditions for electrodeposition of Cd, Cr and Cu (pH, deposition current, time of electrolysis) were studied. Nickel was found to be the best electrode material. The metals accumulate on the surface of electrode and were then evaporated/ablated with a Nd:YAG laser focused into the ICP-OES spectrometer. The detection limits are 0.13 mg?L^?1 for Cd, 0.15 mg?L^?1 for Cu, and 1.9 mg?L^?1 for Cr in case of a stationary bottom working electrode, and 0.25 mg?L^?1 for Cd, 0.05 mg?L^?1 for Cu, 0.8 mg?L^?1 for Cr when using a rotating electrode. The relative standard deviation is in range from 3.8 to 10.3%. Waste water was analyzed in this way by the standard addition method.     

Amperometric Detection of Histamine with a Pyrroloquinoline‐Quinone Modified Electrode

A modified glassy carbon (GC) electrode was developed for the amperometric detection of biogenic amines, particularly histamine. The electrode was modified with the co‐enzyme pyrroloquinoline quinone (PQQ) by entrapment during electropolymerziation of pyrrole to form polypyrrole (PPy). This method formed a thin film on the electrode surface possessing very good stability with a shelf‐life exceeding one month without loss of signal. Optimal conditions for the PQQ/PPy electrode were determined and a linear response was found for histamine in phosphate buffer (pH 6) at +550 mV from 40 to 170 mg L^?1 with a limit of detection (S/N≥3) of 38 mg L^?1. The practical linear range offered by this method suggests ideal use for spoilage detection in fermented foods.     

Development of Polymeric Membrane Sensor for the Determination of Histamine: Experimental and Theoretical Study

Abstract

Some original histamine membrane sensors were prepared by incorporating thiopyrilium (TP) derivative as an excellent charged carrier. Among these sensors, TP2 shows the best response to histamine in a wide concentration range from 2.5×10^?6 to 1.0×10^?1 mol L^?1 with a slope of 55.6±0.7 mV decade^?1 and with a detection limit of 1.0 µmol L^?1 (～0.1 ppm). The interference between histamine and several amino acids and common inorganic anions was negligible as shown by the potentiometric selectivity coefficient data. The prepared electrode was used for the determination of histamine in a human serum synthetic sample. Theoretical calculations were carried out to find the best interactions between histamine and different ligands.     

Adsorptive stripping voltammetry of nickel at a bare glassy carbon electrode

A bare glassy carbon electrode is applied to nickel determination by adsorptive stripping voltammetry in the presence of dimethylglyoxime as a complexing agent. A procedure of nickel determination and electrode regeneration was proposed. The calibration graph for Ni(II) for an accumulation time of 120?s was linear from 2?×?10^?9 to 1?×?10^?7?mol?L^?1. The detection limit was 8.2?×?10^?10?mol?L^?1. The relative standard deviation for a solution containing 2?×?10^?8?mol?L^?1 of Ni(II) was 4.1%. The proposed procedure was applied for Ni(II) determination in certified water reference materials.     

Nanostructured Alpha‐Nickel Hydroxide Electrodes for High Performance Hydrogen Peroxide Sensing

Nanostructured alpha‐nickel hydroxide (α‐Ni(OH)₂) immobilized on a Fluorine‐doped Tin Oxide (FTO) surface was explored for the construction of hydrogen peroxide amperometric Flow Injection Analysis (FIA) sensors. Their notable electrocatalytic activity and heterogeneous electron‐transfer rate were confirmed by the appearance of a broad and intense peak associated with the oxidation of hydrogen peroxide and the enhancement of sensibility in hydrodynamic conditions. The α‐Ni(OH)₂ electrodes exhibited a broad dynamic range (5×10^?6 to 1×10^?3 mol L^?1), low detection limit (2×10^?7 mol L^?1), good repeatability (RSD=1.29 % for 20 successive analyses), and a sensitivity greater than 500 µA mmol^?1 L^?1 cm^?2.     

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.     

First electrochemical study of the fungicide oxycarboxin

In this article, the utility of a boron-doped diamond electrode for the determination of the fungicide oxycarboxin is demonstrated. For the first time, the square-wave voltammetry was employed in a quantitative determination of oxycarboxin on the boron-doped diamond electrode. It was found that oxycarboxin displays a well-expressed oxidation peak at a potential of ca. +1.5 V vs. Ag/AgCl in Britton–Robinson buffer with the maximum response in pH 4.0. As observed in cyclic voltammetry, oxycarboxin undergoes diffusion-controlled irreversible electrochemical oxidation. At optimised square-wave voltammetry parameters, the current response of oxycarboxin was linearly proportional to its concentration in the wide linear dynamic range of 8.0–100.0 μmol L^?1 (2.1–26.7 mg L^?1). The developed electroanalytical method yielded a relatively low limit of detection of 1.6 μmol L^?1 (0.4 mg L^?1), associated with high repeatability of the peak current expressed as relative standard deviation in the range of 1.1–2.9% for each concentration of oxycarboxin solution. This simple and sensitive method was proved to be suitable for an analysis of spiked river water samples with satisfactory results (relative standard deviation of 1.4%, recovery of 100.2%). The impact of possible interferences was tested and evaluated, and obtained results proved good selectivity of the proposed method. In addition, the influence of oxycarboxin on the corrosion properties of AISI 316 L stainless steel used as a construction material in farming was tested using potentiodynamic method, and a corrosive damage was characterised by means of scanning electron microscopy.     

Simultaneous Determination of Nickel and Cadmium by Adsorptive Stripping Voltammetry

A sensitive and fast method for the simultaneous determination of trace amounts of nickel and cadmium in real samples has been described using differential pulse adsorptive stripping voltammetry (DPASV) by adsorptive accumulation of the N,N′‐bis(salicylaldehydo)4‐carboxyphenylenediamine (BSCPDA)–complex on the hanging mercury drop electrode (HMDE). As supporting electrolyte 0.02 mol L^?1 ammonia buffers containing ligand has been used. Optimal analytical conditions were found to be: BSCPDA concentration of 42 μM, pH 9.6 and adsorption potential at ?50 mV versus Ag/AgCl. With an accumulation time of 20 s, the peaks current are proportional to the concentration of nickel and cadmium over the 1–180, and 0.5–200 ng mL^?1 with detection limits of 0.06 and 0.03 ng mL^?1 respectively. The sensitivity of method for determination of nickel and cadmium were obtained 0.54 and 0.98 nA mL ng^?1, respectively. The procedure was applied to simultaneous determination of nickel and cadmium in some real and synthetic artificial samples with satisfactory results.     

Influence of Free Ammonia on Completely Autotrophic Nitrogen Removal over Nitrite (CANON) Process

Free ammonia (FA) plays a significant role in the stable, long-term, completely autotrophic nitrogen removal over nitrite (CANON) system operation. The influence of FA on the CANON process in a sequencing batch biofilm reactor was explored. Under controlled FA concentrations of 5.0?mg L^?1 to 10.0?mg L^?1, nitrite-oxidizing bacteria (NOB) was inhibited and achieved partial nitrification, which was important for a successful and quick start-up of the CANON process from activated sludge. However, NOB was acclimated to the condition after the process start-up. Ammonia-oxidizing bacteria (AOB) and anaerobic ammonium-oxidizing bacteria (AnAOB) activities were unaffected when FA concentration was increased from 10?mg L^?1 to 17?mg L^?1, but NOB was completely inhibited only for a short time. The AOB and AnAOB activities were inhibited and the CANON system was deteriorated when FA concentration reached 30?mg L^?1 to 32.5?mg L^?1 at pH?8.5, whereas NOB activity was unaffected. Correlation analysis showed that FA concentration higher than 20?mg L^?1 resulted in the deterioration of the system.     

Sensitive determination of bisphenol A in plastic products by derivative voltammetry using an acetylene black paste electrode coated with salicylaldehyde-modified chitosan

A sensitive and reliable electrochemical method was developed for determination of bisphenol A (BPA) in plastic products using an acetylene black paste electrode coated with salicylaldehyde-modified chitosan (denoted as S-CHIT/ABPE). In the second-order derivative linear sweep voltammetry technique, BPA yielded a very sensitive and well-defined oxidation peak at 842?mV in 0.2?mol?L^?1 HCl solution. Owing to its unique structure and extraordinary properties, S-CHIT/ABPE showed higher accumulation efficiency toward BPA compared with bare ABPE, and significantly enhanced the oxidation peak current of BPA. Under the optimum conditions, the oxidation peak current was proportional to the concentration of BPA over the range of 4.0?×?10^?8?mol?L^?1?～?1.0?× 10^?5?mol?L^?1. The detection limit (S/N?=?3) was 2.0?×?10^?8?mol?L^?1. The fabricated S-CHIT/ABPE not only exhibited strong adsorption capacity toward BPA, but also provided remarkable stable and quantitatively reproducible analytical performance. Additionally, this newly-developed method possesses some obvious advantages including high sensitivity, extreme simplicity, rapid response and low cost.     

Electrocatalysis Oxidation of GMP Based on Layered Double Hydroxide Functionalized with Anionic Surfactant and Room Temperature Ionic Liquid Modified Glassy Carbon Electrode

The electrocatalysis oxidation of guanosine‐5′‐monophosphate (GMP) was investigated on Mg‐Al layered double hydroxide (LDH) functionalized with sodium dodecyl sulfate (SDS) and room temperature ionic liquid (RTIL) modified glass carbon electrode (GCE). The cyclic voltammogram of GMP on the modified electrode (RTIL/ LDH‐SDS/GCE) exhibited a well defined anodic peak at 1.091 V in 0.2 mol·L^?1 pH 4.4 acetate buffer solution. The GMP oxidation was enhanced in the presence of anionic surfactant in the ?lms. The results suggest that the surfactant molecules intercalate the LDH layers to preconcentrate GMP molecules and the RTIL showed good ionic conductivity. The experimental parameters were optimized, the kinetic parameters were investigated and the probable oxidation mechanism was proposed. Under the optimized conditions, the oxidation peak current was proportional to GMP concentration in the range from 5.0×10^?7 to 1.0×10^?4 mol·L^?1 with the correlation coefficient of 0.9987 and the detection limit was 1.0×10^?7 mol·L^?1. The RTIL/LDH‐SDS/GCE showed a good electrochemical response to the oxidation of GMP and would be developed into a new biosensor.     

Nanoporous Pt Catalyst Modified by Sn Electrodeposition for Electrochemical Oxidation of Formaldehyde

A nanoporous Pt particles‐modified Ti (nanoPt/Ti) electrode was prepared through a simple hydrothermal method using aqueous H₂PtCl₆ as a precursor and formaldehyde as a reduction agent. The nanoPt/Ti electrode was then modified with limited amounts of tin particles generated by cyclic potential scans in the range of ?0.20 to 0.50 V in a 0.01 mol·L^?1 SnCl₂ solution, to synthesize a Sn‐modified nanoporous Pt catalyst (Sn/nanoPt/Ti). Electroactivity of the nanoPt/Ti and Sn/nanoPt/Ti electrodes towards formaldehyde oxidation in a 0.5 mol·L^?1 H₂SO₄ solution was evaluated by cyclic voltammetry and chronoamperometry. Electrooxidation of formaldehyde on the nanoPt/Ti electrode takes place at a potential of 0.45 V and then presents high anodic current densities due to the large real surface area of the nanoPt/Ti electrode. The formaldehyde oxidation rate is dramatically increased on the Sn/nanoPt/Ti electrode at the most negative potentials, where anodic formaldehyde oxidation is completely suppressed on the nanoPt/Ti electrode. Chronoamperogramms (CA) of the Sn/nanoPt/Ti electrode display stable and large quasi‐steady state current densities at more negative potential steps. Amperometric data obtained at a potential step of 100 mV show a linear dependence of the current density for formaldehyde oxidation upon formaldehyde concentration in the range of 0.003 to 0.1 mol·L^?1 with a sensitivity of 59.29 mA·cm^?2 (mol·L^?1)^?1. A detection limit of 0.506 mmol·L^?1 formaldehyde was found. The superior electroactivity of the Sn/nanoPt/Ti electrode for formaldehyde oxidation can be illustrated by a so‐called bifunctional mechanism which is involved in the oxidation of poisoning adsorbed CO species via the surface reaction with OH adsorbed on neighboring Sn sites.     

Determination of Nitrite in Aqueous Solutions using the Linear Sweep Voltammetry Technique

ABSTRACT

An electrochemical method using linear sweep voltammetry techniques was developed to determine nitrite ion in aqueous solution in the presence of nitrate. Nitrite solutions exhibited a well-defined oxidation wave at +1.0V vs SCE at vitreous carbon, while no oxidation process was observed for nitrate solutions. The pH of the nitrite solutions varied from 2.37 to 5.60 and no change was observed in the Ep values, except for the pH 5.60 solution, where little change was verified. The potential also did not vary with change in the nitrite concentration in the 5.0 x 10^?5 to 7.0 x 10^?4 mol L^?1 range. Very good straight lines for plots of current versus nitrite concentration in the 7.0 x 10^?5 to 7.0 x 10^?4 mol L^?1 range were obtained; the correlation coefficient was never worse than 0.990. The nitrite determination was also performed in the presence of 1.0 x 10^?3 mol L^?1 of NO₃ ^? ions. The addition of NO₃ ^? did not change significantly the current values even when it was added in one hundred times molar excess.     

Electrocatalytic Determination of Nitrite on a Rigid Disk Electrode Having Cobalt Phthalocyanine Prepared In Situ

This work reports an in situ cobalt(II) phthalocyanine (CoPc) synthesis on a SiO₂/SnO₂ (SiSn) matrix surface obtained by the sol‐gel method and its electrocatalytic activity for oxidation of nitrite. A rigid disk electrode with SiSn/CoPc was used to study the electrooxidation of nitrite by the cyclic voltammetric, chronoamperometric techniques and differential pulse voltammetry (DPV). The adsorbed phthalocyanine electrocatalyzed nitrite oxidation at 0.73 V (versus SCE) using the DPV technique. The anodic peak current intensities, plotted from differential pulse voltammograms in 1 mol L^?1 KCl for the concentration range 0.002 to 3.85 mmol L^?1 of nitrite were linear, with a correlation coefficient of 0.998 and a detection limit of 0.95 μmol L^?1.