Coulometric Determination of Chromium(VI) and Copper(II) Present Simultaneously

It was shown that chromium(VI) can be determined by coulometry at a Pt electrode in HNO₃and H₂SO₄solutions. A procedure for the determination of 1–4 mg of chromium in 0.5–1 M HNO₃solutions by controlled-potential coulometry with RSD = 0.2% was developed. It was demonstrated that the degree of the reduction of Cr(VI) to Cr(III) reached 99% (RSD = 0.5%) in the determination of chromium by coulometry at a slow potential sweep (v= 1–2 mV/s) in HNO₃solutions. A procedure was proposed for the determination of Cr(VI) and Cu(II) simultaneously present in 0.25–0.5 M H₂SO₄solutions by controlled-potential coulometry with RSD = 0.3%.     

Determination of Vanadium(V) and Vanadium(IV) in Bismuth- and Copper-Containing Compounds by Controlled-Potential Coulometry

It was shown that vanadium(V) and vanadium(IV) can be determined at a large Pt electrode in H₂SO₄ solutions in the presence of copper and bismuth by controlled-potential coulometry with RSD no worse than 0.2%. Compounds of the composition Bi₄V_1.8Cu_0.2O_{10.7 – x} were analyzed.     

Synthesis of hollow and nanoporous gold/platinum alloy nanoparticles and their electrocatalytic activity for formic acid oxidation

In this work, hollow Au/Pt alloy nanoparticles (NPs) with porous surfaces were synthesized in a two-step procedure. In the first step, tri-component Ag/Au/Pt alloy NPs were synthesized through the galvanic replacement reaction between Ag NPs and aqueous solutions containing a mixture of HAuCl₄ and H₂PtCl₄. In the second step, the Ag component was selectively dealloyed with nitric acid (HNO₃), resulting in hollow di-component Au/Pt alloy NPs with a porous surface morphology. The atomic ratio of Au to Pt in the NPs was easily tunable by controlling the molar ratio of the precursor solution (HAuCl₄ and H₂PtCl₆). Hollow, porous Au/Pt alloy NPs showed enhanced catalytic activity toward formic acid electrooxidation compared to the analogous pure Pt NPs. This improved activity can be attributable to the suppression of CO poisoning via the “ensemble” effect.     

Hierarchical TiO2 nanosheet‐assembled nanotubes with dual electron sink functional sites for efficient photocatalytic degradation of rhodamine B

A novel Pt–TiO₂/Ag nanotube photocatalyst has been synthesized successfully via a facile method. TiO₂ nanotubes are assembled with numerous ultrathin TiO₂ nanosheets and show a highly open structure. The gaps between adjacent TiO₂ nanosheets can serve as channels for the access of reactants, accelerating the mass transfer process. During the fabrication process of the Pt–TiO₂/Ag nanotube photocatalyst, high‐quality Pt–SiO₂ nanotubes are synthesized first with the structure‐directing effect of polyvinylpyrrolidone. Then a TiO₂ layer is coated on the outside surface of the silica nanotubes. The introduced titanium species can be converted into TiO₂ nanosheet structure during the subsequent hydrothermal treatment, gradually constructing nanosheet‐assembled nanotubes. Lastly, after the introduction of another electron sink function site of Ag through UV irradiation, the Pt–TiO₂/Ag nanotube photocatalyst with dual electron sink functional sites is obtained. The specially doped Pt and Ag NPs can simultaneously inhibit the recombination process of photogenerated charge carriers and increase light utilization efficiency. Therefore, the as‐synthesized Pt–TiO₂/Ag nanotube catalyst exhibits a high photocatalytic degradation performance for rhodamine B of 0.2 min^?1, which is about 3.2 and 5.3 times as high as that of Pt–TiO₂ and TiO₂ nanotubes because of the enhanced charge carrier separation efficiency. Furthermore, in the unique nanoarchitecture, the nanotubes are assembled with numerous ultrathin TiO₂ nanosheets, which can absorb abundant active species and dye molecules for photocatalytic reaction. On the basis of experimental results, a possible rhodamine B degradation mechanism is proposed to explain the excellent photocatalytic efficiency of the Pt–TiO₂/Ag nanotube photocatalyst.     

Poly(cytosine)‐templated Silver Nanoclusters as Fluorescent Biosensor for Highly Sensitive Detection of Uric Acid

Uric acid (UA) is an important biomarker in urine and serum samples for early diagnosis. This study re‐ ports a fluorescent biosensor based on Poly(cytosine)‐templated silver nanoclusters (C‐Ag NCs) and uricase for the highly sensitive and fast detection of UA. The strong fluorescence of the C‐Ag NCs prepared from poly (cytosine) nucleotides templates could be sensitively quenched by trace amount of H₂O₂, which produced from oxidation reaction of UA catalyzed by uricase. This biosensor exhibits two linear ranges as 50 nM～50 μM and 50 μM～400 μM, with a detection limit of 50 nM. The sensitivity of the biosensor is considerably improved compared with the methods reported in the literature. Furthermore, the detection ability of uric acid in serum samples is confirmed and this C‐Ag NCs‐based uric acid biosensor shows good promise of practical application.     

Nonenzymatic H2O2 Sensor Based on Pt Nanoflower Electrode

A non-enzyme nanosized Pt flower based amperometric sensor for hydrogen peroxide (H₂O₂) is developed. Pt flower were deposited on the gold plated with the method of potentiostatic deposition. The performance of nanosized Pt flower electrode has been characterized with cyclic voltammetric technique and spectroscopic measurements. The Pt nanoparticle can effectively catalyzes the oxidation of H₂O₂ at a favorable potential. The prepared sensor exhibited low detection limit, and quite long-term stability, and it could detect H₂O₂ without any additional mediator or enzyme. The linear range of the Pt/Au electrode toward H₂O₂ is 0.1–0.9?mM, and the detection limit of 0.06?mM was obtained according to 3σ rule. Because of its sensitivity and biocompatibility, it can be used for real sample analysis. The recovery ratio was of 97–106?%, which indicated that the accuracy of this method is also satisfied. It may be widely used in chemical, biological, clinical, food, and environmental fields.     

A Nonenzymatic Glucose Sensor Using Nanoporous Platinum Electrodes Prepared by Electrochemical Alloying/Dealloying in a Water‐Insensitive Zinc Chloride‐1‐Ethyl‐3‐Methylimidazolium Chloride Ionic Liquid

We report here a nonenzymatic sensor by using a nanoporous platinum electrode to detect glucose directly. The electrode was fabricated by electrochemical deposition and dissolution of PtZn alloy in zinc chloride‐1‐ethyl‐3‐methylimidazolium chloride (ZnCl₂‐EMIC) ionic liquid. Both SEM and electrochemical studies showed the evidences for the nanoporous characteristics of the as‐prepared Pt electrodes. Amperometric measurements allow observation of the electrochemical oxidation of glucose at 0.4 V (vs. Ag/AgCl) in pH 7.4 phosphate buffer solution. The sensor also demonstrates significant reproducibility in glucose detection; the higher the roughness factor of the Pt electrode, the lower the detection limit of glucose. The interfering species such as ascorbic acid and p‐acetamidophenol can be avoided by using a Pt electrode with a high roughness factor of 151. Overall, the nanoporous Pt electrode is promising for enzymeless detection of glucose at physiological condition.     

Preconcentration of noble metals on a polymer support as complexes of organic reagents and their subsequent determination in the solid phase

Conditions of the sorption preconcentration of Pt, Pd, Au, Ag, and Hg as colored complexes of azorhodanines, tyrodine, and sulfonitrophenol M from acidic solutions (pH 0–2) on a polyamide membrane in the flow mode are determined. At a flow rate of 10–20 mL/min, concentrations of determined elements of 10^-9-10^-7 M, and pressure of 10–20 mm Hg, the complexes are nearly quantitatively sorbed on a polyamide membrane disk (d = 1 cm,m = 2.7 mg, andl = 0.1 mm). The influence of the composition of the test solutions on the formation of the analytical signal in the solid phase is studied. Rapid sorption-spectrometric procedures are developed for the determination of Pt, Pd, Au, Ag, and Hg with the detection limit 5–30 ng of the element in the sorbent zone     

Pt NPs catalyzed chemiluminescence method for Hg2+ detection based on a flow injection system

Establishing a simple and accurate method for Hg²⁺ detection is of great importance for the environment and human health. In this work, platinum nanoparticles (Pt NPs) with different capped agents and morphologies were synthesized. It was found that Pt NPs exhibited peroxidase‐like activity that can catalyze the chemiluminescence (CL) of the luminol system without H₂O₂. The most intensive CL signals were obtained by using PVP‐capped Pt NPs as catalysis. Based on the fact that Hg²⁺ could further enhance the CL intensity in the Pt NPs‐luminol CL system, a Pt NPs‐catalyzed CL method based on a flow injection system is developed for the sensitive analysis of Hg²⁺. When the concentration of Hg²⁺ in the system increases, the CL intensity would together increase, thereby achieving sensitive Hg²⁺ detection. The limit of detection (LOD) was calculated to be 8.6 nM. This developed method provides a simple and rapid approach for the sensitive detection of Hg²⁺ and shows great promise for applications in other complex systems.     

Graphene–Pt nanocomposite for nonenzymatic detection of hydrogen peroxide with enhanced sensitivity

A sensitive hydrogen peroxide (H₂O₂) sensor was fabricated based on graphene–Pt (GN–Pt) nanocomposite. The GN–Pt was synthesized by photochemical reduction of K₂PtCl₄ on GNs, and characterized by atomic force microscope (AFM), transmission electron microscope (TEM), and energy-dispersive X-ray spectroscopy (EDS). Electrochemical investigations indicated that the GN–Pt exhibited a high peak current and low overpotential towards the reduction of H₂O₂. The GN–Pt modified glass carbon electrode displayed a wide linear range (2–710 μM), low limit of detection (0.5 μM) and good selectivity for detection of H₂O₂ with a much higher sensitivity than that of Pt nanoparticles or graphene modified electrode.     

Simultaneous Detection of Ascorbic Acid and Hydrogen Peroxide by Flow‐Injection Analysis with a Thin Layer Dual‐Electrode Detector

Based on preliminary voltammetric investigations at unmodified and modified electrodes in aqueous solutions buffered at different pHs, a profitable thin layer dual‐electrode detector was developed for the selective and simultaneous determination of ascorbic acid (AA) and hydrogen peroxide present in the same samples. It consists of a small thickness (0.1 mm) cell, used as a detector for a flow injection system, in which a glassy carbon (GC) and a polyeugenol coated Pt electrode are encased. The GC electrode is selective for AA, thanks to the potential applied (0.3 V vs. Ag/AgCl,Cl^?_sat), while H₂O₂ alone can be oxidized at the Pt electrode (0.75 V), thanks to the size selectivity and electrostatic screen properties displayed by the polyeugenol coating layer which prevents oxidation of ascorbate anions. Repeatable sharp peaks (±4.5 %) were detected for both analytes over wide linear ranges (0.005–1.000 mM) and detection limits of about 10^?6 M (176 ppb) and 5×10^?7 M (16 ppb) were inferred for AA and H₂O₂ respectively. This flow injection approach was applied to the analysis of some orange‐taste soft drinks, used as prototype real samples, spiked with controlled amounts of both analytes, thus inferring good recoveries which pointed out that deviations never exceeding 5 % affected the relevant accuracy.     

Pt Nanoparticle‐modified Carbon Fiber Microelectrode for Selective Electrochemical Sensing of Hydrogen Peroxide

We report a simple approach to the production of carbon fiber‐based amperometric microbiosensors for selective detection of hydrogen peroxide (H₂O₂), which was achieved by electrometallization of carbon fiber microelectrodes (CFMs) by electrodeposition of Pt nanoparticles. The Pt‐carbon hybrid sensing interface provided a sensitivity of 7711±587 μA ? mM^?1 ? cm^?2, a detection limit of 0.53±0.16 μM (S/N=3), a linear range of 0.8 μM–8.6 mM, and a response time of <2 sec. The morphologies of the Pt nanoparticle‐modified CFMs were characterized by scanning electron microscopy. To achieve selectivity, permseletive layers, polyphenylenediamine (PPD) and Nafion, were deposited resulting in exclusion of the anionic and cationic interferents, ascorbic acid and dopamine, respectively, at their physiologically relevant concentrations. The resultant sensors displayed a sensitivity to hydrogen peroxide of 1381±72 μA ? mM^?1 ? cm^?2, and a detection limit of 0.86±0.19 μM (S/N=3). This simple and rapid metallization method converts carbon fiber microelectrodes, which are readily accessible, to microscale Pt electrodes in 2 min, providing a platform for oxidase‐based amperometric biosensors with improved spatial resolution over more commonly used platinum electrode array microprobes.     

Electrodeposition of Three‐Dimensional Porous Platinum Film on Removable Polyaniline Template for High‐Performance Electroanalysis

Three‐dimensional porous platinum (Pt_por) films are prepared based on Pt electrodeposition on polyaniline (PANI) modified electrodes followed by selective dissolution of PANI with HNO₃. Electrochemical quartz crystal microbalance data suggest that the PANI‐H₂PtCl₆ interaction involves redox and coordination reactions, depending on the working potential. The Pt_por shows better electrocatalytic performance than the Pt/PANI and conventionally electrodeposited Pt. The Pt_por modified glassy carbon electrode (GCE) can electrocatalyze the oxidation of H₂O₂ with a sensitivity of 414 µA cm^?2 mM^?1 and a detection limit of 9 nM, and the chitosan‐glucose oxidase/Pt_por/GCE can sense glucose with a sensitivity of 93.4 µA cm^?2 mM^?1.     

Electrochemical Behavior and Determination of Hyoscine‐N‐Butylbromide from Pharmaceutical Preparations

The electrooxidation of hyoscine N‐butylbromide (HBB) was investigated by rotating disk electrode voltammetry, cyclic voltammetry and controlled potential coulometry in 0.1 M HNO₃ and in 0.1 M tetrabutylammonium perchlorate (TBAP) solutions of acetonitrile at a platinum (Pt) electrode. Based on the results obtained, it is suggested that a bromide ion of HBB was oxidized in one reversible step in aqueous solutions and in two reversible steps in acetonitrile. A differential pulse voltammetric (DPV) method at a Pt electrode was developed for the determination of HBB in the concentration range of 1.0 × 10^?6‐1.0 × 10^?3 M. The procedure was applied to the determination of HBB in its formulations as well as its recovery from blood serum and urine samples.     

Urchin‐like Ag Nanowires as Non‐enzymatic Hydrogen Peroxide Sensor

Urchin‐like Ag nanowires were prepared by reacting AgNO₃(aq) with Cu metal in the presence of cetyltrimethylammonium chloride and HNO₃(aq) on a screen printed carbon electrode at room temperature. The diameters of the nanowires were about 100 nm, while the lengths were up to 10 μm. Cyclic voltammetric experiments using the Ag nanowires as the working electrode showed electrocatalytic H₂O₂ reduction. The electrode exhibited a high sensitivity of 4705 μA mM^‐1 mg^‐1 cm^‐2 from 50 μM to 10.35 mM and a measurable detection limit of 10 μM in amperometric detection. This is the first report on Ag NWs for non‐enzymatic H₂O₂ sensing.     

An Analyte Derivatization Approach for Improved Electrochemical Detection of Amoxicillin

This paper introduces an interesting analyte derivatization approach for improved electrochemical detection of amoxicillin (one of the most frequently used β‐lactam antibiotics). It is based on the well‐known chemical conversion of catechols to o‐quinones by MnO₂ that can be subsequently easily determined by electrochemical reduction at inexpensive screen‐printed carbon electrodes. The MnO₂ reactor is essential to the proposed amperometric sensor not only to increase the electroactivity but also to achieve the detection selectivity. Under the optimized conditions of applied potential=0.0 V vs. Ag/AgCl and flow rate=500 μL/min, the measurement range was over 3 orders of magnitude with a detection limit (S/N=3) of 17 nM.     

Electrochemical behavior and voltammetric determination of the herbicide metribuzin at mercury electrodes

The electrochemical behavior of the herbicide metribuzin (4-amino-6-tert-butyl-4,5-dihydro-3-methylthio-1,2,4-triazin-5-one) at mercury electrodes was studied in aqueous solutions by direct current (DC) and tast polarography, differential pulse (DPV) and cyclic voltammetry (CV), and controlled-potential coulometry. The electrolysis products were separated and identified by chromatographic techniques combined with mass spectrometric detection. The reduction process in acid media includes two irreversible steps. In the first four-electron step the N–NH₂ and the 1,6-azomethine bonds are reduced. The second step leads to the formation of 5-tert-butyl-2,3,4,5-tetrahydroimidazol-4-one at the mercury-pool electrode. The first reduction step combined with adsorptive accumulation of the herbicide molecule at the mercury electrode surface was used for its determination by differential pulse adsorptive stripping voltammetry (DPAdSV). Calibration curves were linear in the range 1–30 μg L^–1 with a detection limit of 0.27 μg L^–1 (1 nmol L^–1) under the conditions used (buffer pH 4.5, E_acc = –0.45 V relative to Ag/AgCl and t_acc = 10 s). Preconcentration on solid-phase extraction columns (SPE-phenyl) was used for the determination of very small amounts of metribuzin in river water samples. Recovery was approximately 97%. The reproducibility of the analytical procedure including SPE treatment and DPV determination was expressed as relative standard deviations of 2.53 and 3.66% for 2 and 6 μg L^–1 metribuzin, respectively.     

Monolithic integration of three-material microelectrodes for electrochemical detection on PMMA substrates

Monolithic integration of three-material microelectrodes for electrochemical detection on poly (methyl methacrylate) (PMMA) substrates is presented. Au–Ag–Pt three-material electrodes were all fabricated based on polymer compatible photolithography processes, and the fabrication sequence of the electrodes was optimized. The C–Ag–Pt three-electrode system was also demonstrated. To reduce the electrical resistance, the carbon electrode was made on a silver intermediate layer which was simultaneously fabricated with Ag electrodes. A PMMA/poly(dimethylsiloxane) electrochemical sensing microchip with the Au–Ag–Pt three-electrode systems was constructed. The reproducibility of the three-electrode system from single and different microchips was characterized. The performance of the microchip was evaluated by two kinds of electrochemical probes (Ru(bpy)₃Cl₂ and dopamine).     

Ag−Co3O4 @ Nr GO Material Synthesized by One‐pot Hydrothermal Method for Carcinoembryonic Antigen (CEA) Detection of Enzyme‐mimetic Electrochemical Immunosensor

A high‐sensitivity carcinoembryonic antigen immunosensor was successfully prepared via a one‐step hydrothermal method, wherein nitrogen‐doped graphene oxide (Nr GO) loaded Ag and Co₃O₄ nanomaterials were synthesized using ammonia as the nitrogen source. Doping nitrogen atoms into the graphene structure forms a new type of N‐type semiconductor with an increased number of graphene layers and more active sites for bonding with chemicals, thereby providing excellent in biocompatibility and good electrical conductivity. The electrical signal of the sensor is further amplified due to the good catalytic effect of Co₃O₄ and Ag NPs on H₂O₂. The signal probe requires neither pretreatment nor acid treatment, and can be easy to loaded with metal‐immobilized antibodies, which greatly simplifies the detection step not shorten the detection time. The sensor has good sensitivity to detecting carcinoembryonic antigen (CEA) and can easily operate, and requires mild reaction conditions. Under optimal experimental conditions, the linear range of the sensor is 0.001–200 ng ? mL^?1, the detection limit is 0.18 pg ? mL^?1, and the linear correlation coefficient is 0.991, which can be used for CEA determination of the actual sample.     

A Signal‐Amplified Electrochemical Immunosensor Based on Prussian Blue and Pt Hollow Nanospheres as Matrix

Through electrodepositing Prussian blue (PB) and chitosan (CS), then casting Pt hollow nanospheres (HN‐Pt) and assembling CA19‐9 antibody on the electrode surface, an immunosensor was achieved. A new signal amplification strategy based on PB and HN‐Pt toward the electrocatalytic reduction of H₂O₂ was employed when performing the determination. The resulting immunosensor showed a high sensitivity, broad linear response to carbohydrate antigen 19‐9 (CA19‐9) in two ranges from 0.5 to 30 and 30 to 240 U mL^?1 with a low detection limit of 0.13 U mL^?1 (S/N=3). Moreover, it displayed good reproducibility and stability, and would be potentially attractive for clinical immunoassay of CA19‐9.