Simultaneous determination of phenylenediamine isomers and dihydroxybenzene isomers in hair dyes by capillary zone electrophoresis coupled with amperometric detection

The simultaneous determination of three isomers of phenylenediamines (o, m, and p-phenylenediamine) and two isomers of dihydroxybenzenes (catechol and resorcinol) in hair dyes was performed by capillary zone electrophoresis coupled with amperometric detection (CZE–AD). The effects of working electrode potential, pH and concentration of running buffer, separation voltage, and injection time on CZE–AD were investigated. Under the optimum conditions the five analytes could be perfectly separated in 0.30 mol L⁻¹ borate–0.40 mol L⁻¹ phosphate buffer (pH 5.8) within 15 min. A 300 μm diameter platinum electrode had good responses at +0.85 V (versus SCE) for the five analytes. Their linear ranges were from 1.0 × 10⁻⁶ to 1.0 × 10⁻⁴ mol L⁻¹ and the detection limits were as low as 10⁻⁷ mol L⁻¹ (S/N = 3). This working electrode was successfully used to analyze eight kinds of hair dye sample with recoveries in the range 91.0–108.0% and RSDs less than 5.0%. These results demonstrated that capillary zone electrophoresis coupled with electrochemical detection using a platinum working electrode as detector was convenient, highly sensitive, highly repeatable and could be used in the rapid determination of practical samples. Figure Electropherograms obtained from 10 mg mL⁻¹ hair dye sample solutions at a platinum working electrode under optimum CZE–AD conditions: (a) natural black (I), (b) golden: (1) p-phenylenediamine, (2) m-phenylenediamine, (3) o-phenylenediamine, (4) resorcinol, and (5) catechol     

Catalytic Effect on Silver Electrodeposition of Gold Deposited on Carbon Electrodes

A new methodology, based on silver electrocatalytic deposition and designed to quantify gold deposited onto carbon paste electrode (CPE) and glassy carbon electrode (GCE), has been developed in this work. Silver (prepared in 1.0 M NH₃) electrodeposition at ?0.13 V occurs only when gold is previously deposited at an adequate potential on the electrode surface for a fixed period of time. When a CPE is used as working electrode, an adequate oxidation of gold is necessary. This oxidation is carried out in both 0.1 M NaOH and 0.1 M H₂SO₄ at oxidation potentials. When a GCE is used as working electrode, the oxidation steps are not necessary. Moreover, a cleaning step in KCN, which removes gold from electrode surface, is included. To obtain reproducibility in the analytical signal, the surface of the electrodes must be suitably pretreated; this electrodic pretreatment depends on the kind of electrode used as working electrode. Low detection limits (5.0×10^?10 M) for short gold deposition times (10 min for CPE and 5 min for GCE) were achieved with this novel methodology. Finally, sodium aurothiomalate can be quantified using silver electrocatalytic deposition and GCE as working electrode. Good linear relationship between silver anodic stripping peak and aurothiomalate concentration was found from 5.0×10^?10 M to 1.0×10^?8 M.     

多壁碳纳米管修饰金膜塑料电极测定儿童用品中的壬基酚

以廉价的聚对苯二甲酸乙二酯(PET)塑料为基底,采用真空离子溅射技术,制备了一种多壁碳纳米管修饰的可抛式金膜塑料工作电极.通过扫描电镜观察修饰电极的表面形貌,利用循环伏安法对不同修饰状态的电极性能进行表征.在优化实验条件下,应用线性扫描伏安对壬基酚(NP)进行分析.结果表明,壬基酚在0.05-5 mg/L范围内,修饰工...     

Sensitive quantification of iodide by ion-exchange chromatography with electrochemical detection at a modified platinum electrode

A rapid and very sensitive method for the accurate determination of free iodide in real samples is described. The method is based on anion-exchange chromatographic separation coupled with amperometric detection at a modified platinum electrode under constant applied potential (+0.85 V vs. Ag AgCl). An experimental setup with an in-line and very effective method of electrode modification is proposed using an amperometric thin-layer cross-flow detector and a flowing solution 300 mg/L of iodide; the working electrode is polarised to the limiting current for oxidation of iodide to iodine in acidic solutions with the consequent formation of an iodine-based film. The results indicated that the modified electrode exhibits high analytical response for iodide electrooxidation with good stability and long-life. The signal intensity of daily experimental sessions (8 h), during which standards and real samples were repeatedly injected, exhibits a moderate lowering (i.e. <6%). Using a mixture of 25 mM HNO₃ and 50 mM NaNO₃ as an eluent phase in ion-exchange chromatography, the detection limit of iodide was estimated to be 0.5 g/L (S/N=3) with an injection volume of 50 L. This method was applied successfully to quantify the iodide content of milk samples and in wastewaters as well as trace amounts in common vegetables and solutions containing high chloride levels.     

Preparation and application of a new glucose sensor based on iodide ion selective electrode

An electrode for glucose has been prepared by using an iodide selective electrode with the glucose oxidase enzyme. The iodide selective electrode used was prepared from 10% TDMAI and PVC according our previous study. The enzyme was immobilized on the iodide electrode by holding it at pH 7 phosphate buffer for 10 min at room temperature. The H₂O₂ formed from the reaction of glucose was determined from the decrease of iodide concentration that was present in the reaction cell. The iodide concentration was followed from the change of potential of iodide selective electrode. The potential change was linear in the 4×10⁻⁴ to 4×10⁻³ M glucose concentration (75-650 mg glucose/100ml blood) range. The slope of the linear portion was about 79 mV per decade change in glucose concentration. Glucose contents of some blood samples were determined with the new electrode and consistency was obtained with a colorimetric method. The effects of pH, iodide concentration, the amount of enzyme immobilized and the operating temperature were studied. No interference of ascorbic acid, uric acid, iron(III) and Cu(II) was observed. Since the iodide electrode used was not an AgI-Ag₂S electrode, there was no interference of common ions such as chloride present in biological fluids. The slope of the electrode did not change for about 65 days when used 3 times a day.     

Electrodeposition of dendritic gold/silver nanaoparticles on disposable screen‐printed carbon electrode and its application of 4‐mercaptopyridine in in situ electrochemical surface‐enhanced Raman scattering

Column electrodes pretreated through oxidation–reduction cycles were traditionally used in electrochemical surface‐enhanced Raman scattering (SERS). In this study, a disposable screen‐printed carbon electrode was introduced into in situ electrochemical SERS through the electrodeposition of dendritic gold/silver nanoparticles (Au/AgNPs) onto the surface of the carbon working electrode to induce the SERS enhancement effect on the electrode. Scanning electron microscopy images showed that dendritic Au/AgNPs nanostructures could be fabricated under appropriate electrodeposition conditions and could present a minimum SERS factor of 4.25 × 10⁵. Furthermore, the absorbed behavior of 4‐mercaptopyridine was investigated under different potentials. The adsorption configuration was inferred to transform from ‘vertical’ to ‘lying‐flat’. The proposed new electrode combined with a portable Raman spectrometer could be useful in the identifying products or intermediates during electrochemical synthesis or electrochemical catalysis in in situ electrochemical SERS. Copyright © 2016 John Wiley & Sons, Ltd.     

As(III) Voltammetric Detection by Means of Disposable Screen‐Printed Gold Electrochemical Sensors

Abstract

In this paper a disposable gold screen‐printed working electrode was tested for arsenic detection in aqueous solutions using Square Wave Anodic Stripping Voltammetry (SWASV). The dynamic range of the sensor and its response were characterised in standard As(III) solutions; particular efforts were devoted to optimize electrode surface conditioning and electrolyte solution composition. The detection limit was 2.5 µg l^?1 using 60 s as deposition time. A portable battery‐operated device was used to demonstrate the possibility to use the sensor for on‐site analysis. Analysis of spiked samples was also performed.     

Anodic Stripping Voltammetry Using a Vibrating Electrode

This work proposes a vibrating microwire electrode as working electrode in stripping voltammetry. The vibration was found to maintain a constant and thin (1–2 μm) diffusion layer during the deposition step. The electrode vibration eliminated the need for external stirring of the solution, thus facilitating in situ detection in the environment. The vibration was effected by fixing a low‐voltage (3 V), asymmetric, electrical rotor to the working electrode (a gold microwire of either 5 or 25 μm). The sensitivity of the vibrated electrode was ca. 22×greater than stationary. Measurements of copper (4 nM) by anodic stripping voltammetry using the vibrating electrode had a low standard deviation (1% for n=6) indicating that the diffusion layer had only minor variability. The agitation mechanism was unaffected by water moving at >2 m s^?1 and by water pressure equivalent to a depth of >40 m, indicating its suitability for in situ measurements. The vibrating probe was used for in situ detection of copper by anodic stripping voltammetry to a depth of 6 m. Using a 5 min deposition time, the limit of detection for labile copper was 38 pM.     

Application of Tetra Cyclohexyl Tin(IV) as an Anionic Carrier for the Construction of a New Salicylate Membrane Sensor

A new tin complex namely tetracyclohexyl tin(IV) (TCHT) was synthesized and used as the ion carrier for the construction of a highly selective salicylate sensor. This sensor shows a Nernstian response to salicylate ions over a very wide concentration (1.0 × 10^?7–1.0 × 10^?1 M) in a pH range of 5.5–10.5. The optimum selectivity and response could be obtained for a membrane incorporating 30% PVC, 61% BA, 3% of cationic additive (HTAB) and 6% of TCHT. The response time of the electrode is very short in the whole concentration range (15 s). The electrode also shows an excellent discriminating ability for salicylate ions with respect to the most common organic and inorganic anions including chloride, sulfate, nitrate, nitrite, cyanide, sulfite, iodide, thiocyanate, phosphate, acetate, oxalate, citrate, and tartarate ions. The detection limit of the proposed sensor is 8.0 × 10^?8 M. The electrode was successfully used for determining the concentration of salicylate ion in synthetic serums.     

Determination of TNT and its metabolites in water samples by voltammetric techniques

Square-wave voltammetry with the hanging drop mercury electrode as the working electrode was used for the determination of ultratraces of explosives in aqueous solution. It was shown that the strong pressure dependence of the pneumatically controlled multimode electrode system of a conventional Metrohm apparatus could be compensated by an additional pressure regulation, through which the pressure variations could be decreased when switching from deaeration to the static measurements. By using square-wave voltammetry with this electrode system after this modification the limits of detection for 2,4,6-trinitrotoluene (TNT) and other TNT-metabolites could be decreased down to 0.2 μg L⁻¹ when using a measurement time of 6 min. Also a simultaneous determination of TNT and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) was shown to be possible over a wide linear range and the detection limits then were 2.2 μg L⁻¹ for TNT and 25 μg L⁻¹ for RDX. By applying the highly stable and adjustable pressure as mentioned before, the calibrations could be kept stable over a period of up to 1 week.     

Rapid-scanning electrochemical detector with micro working electrode for micro high-performance liquid chromatography

Summary A voltammetric system controlled by a personal computer was developed using a PC-8801 mk II computer (NEC, Tokyo, Japan) for rapid-scanning voltammetry. The system was combined with an ultra-small-volume electrolytic cell with a single-carbon-fiber (7-μm diameter and 3-mm length) working electrode and used as a new detector for micro high-performance liquid chromatography. The system's capability for the detection of catecholamines and their related compounds was investigated. Three-dimensional voltamo-chromatograms were obtained by adding the potential axis of the electrode to the conventional current and time axes, leading to a dramatic improvement in the identification of each chroamtographic peak.     

Carbon nanoparticle modified screen printed carbon electrode as a disposable electrochemical immunosensor strip for the detection of Japanese encephalitis virus

The authors describe a disposable electrochemical immunosensor strip for the detection of the Japanese encephalitis virus (JEV). The assay is based on the use of a screen printed carbon electrode (SPCE) modified with carbon nanoparticles (CNPs) that were prepared from starch nanoparticles and deposited on the SPCE working electrode whose surface was functionalized with 3-aminopropyl triethoxysilane. Next, antibody of JEV was immobilized on the surfaces of the CNPs. The analytical performance of immunosensor strip was characterized using cyclic voltammetry (with hexacyanoferrate as the redox probe) and electrochemical impedance spectroscopy. The deposition of CNPs enhances the electron transfer kinetics and current intensity of the SPCE by 63% compared to an unmodified SPCE. Under optimized conditions, the calibration plot is linear within the 5–20 ng·mL^?1 JEV concentration range, the limit of detection being 2 ng·mL^?1 (at an S/N ratio of 3), and the assay time is 20 min. This immunosensor strip was successfully applied to the detection of JEV in human serum samples. It represents a cost-effective alternative to conventional diagnostic tests for JEV.

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Graphical abstract A disposable carbon nanoparticles modified screen printed carbon electrode (SPCE) immunosensor strip for Japanese encephalitis virus (JEV) detection is described. A limit of detection of 2 ng·mL^?1 and an assay time of 20 min were achieved.

     

Iodide‐Selective Electrode Based on Copper Phthalocyanine

Copper phthalocyanine was used as ion carrier for preparing polymeric membrane selective sensor for detection of iodide. The electrode was prepared by incorporating the ionophore into plasticized poly(vinyl chloride) (PVC) membrane, coated on the surface of graphite electrode. This novel electrode shows high selectivity for iodide with respect to many common inorganic and organic anions. The effects of membrane composition, pH and the influence of lipophilic cationic and anionic additives and also nature of plasticizer on the response characteristics of the electrode were investigated. A calibration plot with near‐Nernestian slope for iodide was observed over a wide linear range of five decades of concentration (5×10^?6?1×10^?1 M). The electrode has a fast response time, and micro‐molar detection limit (ca. 1×10^?6 M iodide) and could be used over a wide pH range of 3.0–8.0. Application of the electrode to the potentiometric titration of iodide ion with silver nitrate is reported. This sensor is used for determination of the minute amounts of iodide in lake water samples.     

Copper(I)-bathocuproine complex as carrier in iodide-selective electrode

A PVC membrane electrode for iodide ions based on Cu(I)-bathocuproine as ionophore in membrane composition is prepared. The electrode exhibits a linear response over a wide concentration range 5.0×10⁻⁶ to 2.0×10⁻¹ mol l⁻¹ with a detection limit 1.0×10⁻⁶ mol l⁻¹. The proposed membrane electrode shows Nernstian behavior with a slope of −56.8 mV/decade, a fast response time 10 s and a lifetime at least 3 months. Iodide-selective electrode reveals good selectivities for iodide ion over a wide variety of the other anions and can be used in pH range of 3-9. It can also be used as an indicator electrode in potentiometric titration of iodide ion.     

Determination of Nitrite With A Ptfe-Membrane,Covered Electrode After Reduction To Nitrogen Oxide,In A Reagent Saving Flow Injection System

ABSTRACT

Nitrite was reduced in acidic potassium iodide solution to produce nitrogen oxide which was measured amperometrically by a modified gold electrode covered with a PTFE-membrane as the permeability barrier for interfering substances in the sample. The calibration curve was linear up to 30 μM of nitrite and 10 samples could be determined per hour. The average current and the standard deviation for 10 μM standard solution (N=10) were 1.51 x 10^-2 μA and 6.4 x 10^-5 μA (RSD=0.42 %), respectively. The detection limit was 0.25 μM. No response was observed for electrochemical interferant substances such as ascorbic acid and FeSO⁴. The reducing reagent could be reused. Recovery tests were satisfactory (101-103%). The results obtained with this sensor and with the diazotization method for a fish culture water agreed within 8.6%.     

Use of disposable gold working electrodes for cation chromatography-integrated pulsed amperometric detection of sulfur-containing amino acids

We have prepared disposable thin-film gold working electrodes on polymeric substrates. Our microfabrication process allows for inexpensive and reproducible mass production of such electrodes. We utilize this new type of electrode in flow-through electrochemical cells to replace the conventional non-disposable gold working electrodes for integrated pulsed amperometric detection (IPAD) of compounds separated by high-performance cation-exchange chromatography. Using two S-containing amino acids (homocysteine and cysteine) as test compounds, we have modified a previously reported waveform for optimum performance with disposable gold electrodes. With the help of the same two test substances we have characterized the analytical performance of disposable gold electrodes under the new conditions. Compared to non-disposable working electrodes, the disposable working electrodes generated equal or better results in the limit of detection, linearity of calibration and reproducibility. When used with a new IPAD waveform, the disposable electrodes functioned reproducibly for 3 days. At the end of the specified usage period of 3 days, the disposable electrodes are simply replaced. Reconditioning by polishing is thus no longer required.     

Construction of Suitable Iodide–Selective Electrode Based on Phenyl Mercury (II)(2‐mercaptobezothiozolate) Carrier

Abstract

Highly selective poly(vinyl chloride) (PVC) membrane electrode based on recently synthesized mercury complex i.e., phenyl mercury (II) (2‐mercaptobezothiozolate) (PMMBT) as new carrier for iodide‐selective electrode by incorporating the membrane ingredients on the surface of graphite electrode are reported. The effect of various parameters including the membrane composition, pH, and possible interfering anions were investigated on the response properties of the electrode. The developed sensor exhibited Nernstian responses toward iodide over a wide concentration range of 1×10^?7 to 0.1 M with slopes of 57.6±0.8 mV per decade of iodide concentration and detection limit of 8×10^?8 M, over a wide pH ranges of 2.0–11.5. The sensors have response time of 0.5 s and can be used for at least 2 months without any considerable divergence in their potential response. The proposed electrode show good ability to discriminate iodide over several inorganic and organic anions.

The electrode was successfully applied to direct determination of iodide in synthetic mixture, waste water and drinking water, and pharmaceutical samples in addition to applying as indicator electrode in precipitation titration.     

AgNP/Bi/Nafion‐modified Disposable Electrodes for Sensitive Zn(II), Cd(II), and Pb(II) Detection in Aerosol Samples

A new method for modifying electrodes with Ag nanoparticles (AgNPs) using electrospray deposition for sensitive, selective detection of Zn(II), Cd(II), and Pb(II) in aerosol samples when combined with Bismuth and Nafion coating and square‐wave anodic stripping voltammetry (SWASV) is reported. Carbon stencil‐printed electrodes (CSPEs) fabricated on a polyethylene transparency (PET) sheet were produced for an inexpensive, simple to fabricate, disposable sensor that can be used with the microliter sample volumes for analysis. Sensor performance was improved by modifying the electrode surface with electrospray‐deposited AgNPs. The use of electrospray deposition resulted in more uniform particle dispersion across the electrode surface when compared to drop‐casting. Using AgNP‐modified electrodes combined with Bi and Nafion, experimental detection limits (LODs) of 5.0, 0.5, and 0.1 μg L⁻¹ for Zn(II), Cd(II), and Pb(II), respectively, were achieved. The linear working ranges were 5.0–400.0 μg L⁻¹, 0.5–400.0 μg L⁻¹, and 0.1–500.0 μg L⁻¹ for Zn(II), Cd(II), and Pb(II), respectively. Interference studies showed Cu(II) was the only metal that interfered with this assay but inference could be eliminated with the addition of ferricyanide directly to the sample solution. This electrochemical sensor was applied for the simultaneous determination of Zn(II), Cd(II), and Pb(II) within source particulate matter (PM) samples collected on filters using an aerosol test chamber.     

Ketoconazol‐Triiodide Ion Pair Complex as a Suitable Carrier in an Iodide Selective Membrane Electrode

A novel membrane sensor for selective monitoring of iodide, consisting of a triiodide‐ketoconazole ion pair complex dispersed in a PVC matrix, plasticized with a mixture of 2‐nitrophenyl octyl ether and dioctylphtalate with unique selectivity toward iodide ions, is described. The influence of membrane composition, pH of test solution and foreign ions on the electrode performance were investigated. The optimized membrane demonstrates a near‐Nernstian response for iodide ions over a wide linear range from 1.0 × 10^?2 to 1.0 × 10^?5 M, at 25 ± 1 °C. The electrode could be used over a wide pH range 3–10 and has the advantages of high selectivity, fast response time and good lifetime (over 4 months). It was successfully used as indicator electrode in potentiometric titrations and direct potentiometric assay of iodide ions.     

Electrochemical determination of iodide by poly(3-aminophenylboronic acid) film electrode at moderately low pH ranges

A new potentiometric sensor for the determination of iodide based on poly(3-aminophenylboronic acid) (PAPBA) film electrode was constructed. Poly(3-Aminophenylboronic acid) films were synthesized electrochemically on platinum electrode by cyclic voltammetry. The effect of film thickness, pH, and preconditioning parameters on the electrode performance were examined. The analytical performance was evaluated and linear calibration graphs were obtained in the concentration range of 10⁻⁶ to 10⁻¹ M iodide ion. The limit of detection was found to be 8 × 10⁻⁷ M. The response time of the sensor was 5 s and its lifetime is about one week. To check the selectivity of the PAPBA film for iodide ion, potential interferences such as Cl⁻, Br⁻, F⁻, CN⁻, IO₃⁻, Ca²⁺, and Mg²⁺ were tested. The PAPBA electrode was also employed as a sensing platform for the determination of iodide ions in commercial table salt.