A semi-hierarchic computer network for data acquisition and control in staircase voltammetry

A simple computer system designed for controlling voltammetric experiments has been implemented. The system connects a Hewlett-Packard 2100A minicomputer with a Texas Instruments 9900 microcomputer by means of a bidirectional serial transmission link. Experimental parameters are down-loaded from the host to the satellite which supervises the experiments at a remote location. The data collected are transmitted back to the host at 2400 baud for reduction and plotting. Through this division of labor, each system is used to its best advantage. Although the software developed is specifically for staircase voltammetry, the system hardware is of general-purpose design which is suited for other types of pulse experiment.     

Facile cation electro-insertion into layer-by-layer assembled iron phytate films

Molecular layer-by-layer assembly from pre-saturated aqueous solutions of Fe³⁺ and phytate is employed to build up iron phytate deposits on tin-doped indium oxide (ITO) electrodes. Globular films with approximately 1 nm growth per layer are observed by AFM imaging and sectioning. In electrochemical experiments the iron phytate films show well-defined voltammetric responses consistent with an immobilised Fe(III/II) redox system in aqueous (LiClO₄, NaClO₄, KClO₄, phosphate buffer) and in ethanolic (LiClO₄, NaClO₄, NBu₄ClO₄) electrolyte solutions. The Fe(III/II) redox system is reversible and cation insertion/expulsion occurs fast on the timescale of voltammetric experiments even for more bulky NBu₄⁺ cations and in ethanolic solution. Peak shape analysis and scan rate dependent midpoint potentials suggest structural changes accompanying the redox process and limiting propagation. Iron phytate is proposed as a versatile and essentially colourless cation electro-insertion material and as a potential energy storage material.     

Spectrophotometric and voltammetric characterization of a novel selective electroactive chemosensor for Mg2+

A novel azocalix[4]arene derivative, 5,11,17,23-tetrakis[(acetophenone)azo]-25,26,27,28-tetrahydroxycalix[4]arene (APC4), containing acetophenone azo groups at the upper rim was synthesized as a chemosensor. Its binding and sensing properties with alkali and alkaline earth metal ions (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺) were investigated by UV-vis spectrophotometric and voltammetric techniques. The stoichiometric ratio and the association constant were determined spectrophotometrically as 1:1 and (1.94±0.31)×10⁵ L mol^?1 for the complex between Mg²⁺ and the chemosensor, respectively. Moreover, it was shown that the interaction between Mg²⁺ and the APC4 occurred by means of the phenol groups at the lower rim by voltammetric methods. The results of spectrophotometric and voltammetric experiments showed that the chromogenic chemosensor has high selectivity towards Mg²⁺ among the other used metal ions, especially the interfering Ca²⁺ ion.      

Electroanalytical Determination of Promethazine Hydrochloride in Pharmaceutical Formulations on Highly Boron‐Doped Diamond Electrodes Using Square‐Wave Adsorptive Voltammetry

The electrochemical oxidation of promethazine hydrochloride was made on highly boron‐doped diamond electrodes. Cyclic voltammetry experiments showed that the oxidation mechanisms involved the formation of an adsorbed product that is more readily oxidized, producing a new peak with lower potential values whose intensity can be increased by applying the accumulation potential for given times. The parameters were optimized and the highest current intensities were obtained by applying +0.78 V for 30 seconds. The square‐wave adsorptive voltammetry results obtained in BR buffer showed two well‐defined peaks, dependent on the pH and on the voltammetric parameters. The best responses were obtained at pH 4.0, frequency of 50 s^?1, step of 2 mV, and amplitude of 50 mV. Under these conditions, linear responses were obtained for concentrations from 5.96×10^?7 to 4.76×10^?6 mol L^?1, and calculated detection limits of 2.66×10^?8 mol L^?1 (8.51 μg L^?1) for peak 1 and of 4.61×10^?8 mol L^?1 (14.77 μg L^?1) for peak 2. The precision and accuracy were evaluated by repeatability and reproducibility experiments, which yielded values of less than 5.00% for both voltammetric peaks. The applicability of this procedure was tested on commercial formulations of promethazine hydrochloride by observing the stability, specificity, recovery and precision of the procedure in complex samples. All results obtained were compared to recommended procedure by British Pharmacopeia. The voltammetric results indicate that the proposed procedure is stable and sensitive, with good reproducibility even when the accumulation steps involve short times. It is therefore very suitable for the development of the electroanalytical procedure, providing adequate sensitivity and a reliable method.     

富锂掺杂Li1.06Co0.05Cr0.1Mn1.85O4的合成及电化学性能研究

锂离子电池具有比能量高、功率大、使用寿命长、无记忆效应、性能价格比高等优点,从而成为可充式电源的主要选择对象.锰由于资源丰富、价廉、环境友好等优点,使锰酸锂(LiMn2O4)成为最有希望取代钴酸锂的正极材料.但锰酸锂的放电容量相对较低,结构欠稳定,容量衰减严重,作为正极材料还无法与钴酸锂相比,近年来做了大量的研究工作以改善它的电化学性能[1～6].最近Youngjoon Shin等研究发现[7]用少量的Li与Ni共同替代LiMn2O4中的Mn得到的LiMn2-2yLiyNiyO4的电化学性能要优于单元素替代的LiMn2-xMxO4(M=Li,Cr,Fe,Co,Ni)的电化学性能.     

Electro-Catalytic Oxidation of Ascorbic Acid at a Cobalt-Salen Polymer Modified Electrode and Analytical Applications

ABSTRACT

The preparation and electrochemical characteristics of electrodes modified by cobalt complexes of N, N' - bis(salicylidene)-ethane -1, 2- diamine (salen) are described. A cobalt-salen polymer film modified electrode has strong electro-catalytic effects for the oxidation of ascorbic acid. The anodic peak potential of ascorbic acid shifted negatively for 400 m V. The catalytic reaction rate constant determined by rotating disk experiments is 7.08×10⁵ mol s^?1 cm^3. The catalytic mechanism and the effect of film thickness are discussed. A sensitive voltammetric response for ascorbic acid was obtained covering a linear range from 1.0×10^?6 to 1.0×10^?3 mol-L^?1 The modified electrode showed good stability and reproducibility. The electrode was used to the determination of ascorbic acid in fruit juices and showed promising results compared with conventional methods. The electro-catalytic effect of several metal-salen complexes and a similar Schiff base derivative for ascorbic acid was compared.     

An improved ELISA for the determination of tobacco mosaic virus with linear sweep voltammetry detection based on a new system of PAP-H2O2-HRP

An improved ELISA for the determination of tobacco mosaic virus (TMV) with linear sweep voltammetry based on a new system of p-aminophenol (PAP)- H₂O₂- horseradish peroxidase (HRP) has been developed. The enzymatic product 3-[(4-hydroxyphenyl)amino]-4-(2-amino-5-hydroxyphenyl)-6-[(4-hydroxyphenyl)imino]-2,4-cyclohexadiene-1-one, produced from HRP catalyzing the oxidation of PAP with H₂O₂, yields a sensitive linear sweep voltammetric response at a potential of –0.45 V (vs. SCE) in Britton-Robinson (BR) buffer solution. By using this voltammetric peak, HRP can be measured with a detection limit of 0.4 mU/L and a linear range of 1.0 ～ 1.0 × 10² mU/ L. The detection limit for the clarified TMV is 4.0 ng/mL and the highest dilution ratio detected for the infected leaf sap is 1?:?3.9 × 10⁶. The processes of the enzyme-catalyzed reaction and the electro-reduction of the product of the enzyme-catalyzed reaction have been investigated.     

Captopril Modified Silver Electrode and Its Application to the Electroanalysis of Hemoglobin

Abstract

Captopril, 1-[(2S)-3-mercapto-2-methyl-1-oxopropyl]-L-Proline, can be deposited onto a silver electrode by a covalent bonding method to give a long-lived and stable chemically modified electrode(CME). Since the CME is prepared with a reaction between captopril and the substrate silver, the CME being prepared by this method is very stable. Furthermore, Hemoglobin(Hb) exhibits excellent voltammetric response at the modified electrode. Differential pulse voltammetric(DPV) measurements of the protein with this CME reveal the existence of a linear relationship between the anodic peak current and the concentration of Hb in the range of 2×10^?6 ～ 5×10^?5 mol/L. The detection limit is 8×10^?7 mol/L and the relative standard deviation of results is 5% for 6 successive determinations at 2×10_-5 mol/L. The determination of Hb for a real example is carried out.     

Synthesis of novel chromogenic azocalix[4]arenemonoquinones and their binding with alkali metal cations

Five new chromogenic azocalix[4]arenemonoquinones have been synthesized, characterized and examined for their interaction with alkali metal cations (Li⁺, Na⁺, K⁺, Rb⁺ and Cs⁺) by UV-visible spectroscopic and cyclic voltammetric techniques. It has been determined that 4a selectively exhibits a significant bathochromic shift in its UV-visible spectrum on interaction with potassium ion in comparison to its treatment with other alkali metal cations. The binding stoichiometry of 4a and potassium ion was established to be 1:1 with an association constant of 3.27 × 10⁴ M^?1. Cyclic voltammetric experiments in 4:1 dichloromethane-acetonitrile also revealed a significant anodic shift (ΔE _(1/1′) = 115 mV) of the original redox waves of 4a on interaction with potassium ion.     

Sequential injection anodic stripping voltammetry with monosegmented flow and in-line UV digestion for determination of Zn(II), Cd(II), Pb(II) and Cu(II) in water samples

A cost-effective sequential injection system incorporating with an in-line UV digestion for breakdown of organic matter prior to voltammetric determination of Zn(II), Cd(II), Pb(II) and Cu(II) by anodic stripping voltammetry (ASV) on a hanging mercury drop electrode (HMDE) of a small scale voltammetric cell was developed. A low-cost small scale voltammetric cell was fabricated from disposable pipet tip and microcentrifuge tube with volume of about 3 mL for conveniently incorporated with the SI system. A home-made UV digestion unit was fabricated employing a small size and low wattage UV lamps and flow reactor made from PTFE tubing coiled around the UV lamp. An in-line single standard calibration or a standard addition procedure was developed employing a monosegmented flow technique. Performance of the proposed system was tested for in-line digestion of model water samples containing metal ions and some organic ligands such as strong organic ligand (EDTA) or intermediate organic ligand (humic acid). The wet acid digestion method (USEPA 3010a) was used as a standard digestion method for comparison. Under the optimum conditions, with deposition time of 180 s, linear calibration graphs in range of 10-300 μg L⁻¹ Zn(II), 5-200 μg L⁻¹ Cd(II), 10-200 μg L⁻¹ Pb(II), 20-400 μg L⁻¹ Cu(II) were obtained with detection limit of 3.6, 0.1, 0.7 and 4.3 μg L⁻¹, respectively. Relative standard deviation were 4.2, 2.6, 3.1 and 4.7% for seven replicate analyses of 27 μg L⁻¹ Zn(II), 13 μg L⁻¹ Cd(II), 13 μg L⁻¹ Pb(II) and 27 μg L⁻¹ Cu(II), respectively. The system was validated by certified reference material of trace metals in natural water (SRM 1640 NIST). The developed system was successfully applied for speciation of Cd(II) Pb(II) and Cu(II) in ground water samples collected from nearby zinc mining area.     

Flow-injection determination of meptazinol with electrochemical detection

A flow-injection analysis system incorporating a glassy carbon voltammetric detector cell is described. Meptazinol (0.01–10 μg ml^-1) can be determined by electro-chemical oxidation in a carrier stream of 0.05 M sodium acetate—0.1 M acetic acid in 98% ethanol at sampling rates up to 80 samples per hour.     

Voltammetric determination of N-alkylated anilines by adsorption/extraction at a carbon-paste electrode

The voltammetric behaviour of aniline and some of its N-alkylated derivatives at a carbon-paste (Nujol/graphite) electrode is examined. The N-alkylated anilines, in contrast to aniline, are accumulated at the electrode by a combined adsorption/extraction process. The organic bases are determined in the rane 10^?7?2×10^?6 M after a 2-min preconcentration period by differential pulse voltammetry; N,N-dimethylaniline can be determined in the presence of excess of aniline (10^?5 M) by using medium-exchange. The voltammetric method is used for evaluation of the distribution ratios of the organic bases in the Nujol/aqueous buffer system. The enhancement of the voltammetric signal of each base is correlated with the respective distribution ratio.     

Die bestimmung von alizarin s nach der anreicherung am stationären quecksilbertropfen und ihre anwendung zur fluoridanalyse

Traces of alizarin S can be concentrated on the stationary mercury electrode. The lower limit for the production of d.c. voltammograms is 5·10^-9M. The voltammetric spectrum of the dyestuff was examined by means of d.c. and a.c. polarographic techniques. An indirect voltammetric method for the determination of fluoride in the range 5·10^-7–5·10^-6M is suggested.     

An enzymeless organophosphate pesticide sensor using Au nanoparticle-decorated graphene hybrid nanosheet as solid-phase extraction

A sensitive enzymeless organophosphate pesticides (OPs) sensor is fabricated by using Au nanoparticles (AuNPs) decorated graphene nanosheets (GNs) modified glassy carbon electrode as solid phase extraction (SPE). Such a nanostructured composite film, combining the advantages of AuNPs with two dimensional GNs, dramatically facilitates the enrichment of nitroaromatic OPs onto the surface and realizes their stripping voltammetric detection of OPs by using methyl parathion (MP) as a model. The stripping voltammetric performances of captured MP were evaluated by cyclic voltammetric and square-wave voltammetric analysis. The combination of the nanoassembly of AuNPs-GNs, SPE, and stripping voltammetry provides a fast, simple, and sensitive electrochemical method for detecting nitroaromatic OPs. The stripping analysis is highly linear over the MP concentration ranges of 0.001-0.1and 0.2-1.0 μg mL⁻¹ with a detection limit of 0.6 ng mL⁻¹. This designed enzymeless sensor exhibits good reproducibility and acceptable stability.     

An improved ELISA for the determination of tobacco mosaic virus with linear sweep voltammetry detection based on a new system of PAP-H2O2-HRP

An improved ELISA for the determination of tobacco mosaic virus (TMV) with linear sweep voltammetry based on a new system of p-aminophenol (PAP)- H₂O₂- horseradish peroxidase (HRP) has been developed. The enzymatic product 3-[(4-hydroxyphenyl)amino]-4-(2-amino-5-hydroxyphenyl)-6-[(4-hydroxyphenyl)imino]-2,4-cyclohexadiene-1-one, produced from HRP catalyzing the oxidation of PAP with H₂O₂, yields a sensitive linear sweep voltammetric response at a potential of –0.45 V (vs. SCE) in Britton-Robinson (BR) buffer solution. By using this voltammetric peak, HRP can be measured with a detection limit of 0.4 mU/L and a linear range of 1.0 ∼ 1.0 × 10² mU/ L. The detection limit for the clarified TMV is 4.0 ng/mL and the highest dilution ratio detected for the infected leaf sap is 1 : 3.9 × 10⁶. The processes of the enzyme-catalyzed reaction and the electro-reduction of the product of the enzyme-catalyzed reaction have been investigated. Received: 17 November 1998 / Revised: 17 March 1999 / Accepted: 20 March 1999     

The electrode modified with Langmuir–Blodgett film of p-tert-butylcalix[4]arene derivatives with sulfur-containing functionalities for the determination of silver

A new voltammetric sensor, based on a new p-tert-butylcalix[4]arene derivative (TCAD) modified glassy carbon electrode (GCE) using Langmuir–Blodgett (LB) technique, was designed successfully and used for recognition and determination of Ag⁺. The π?-?A isotherms suggested that the monolayer of TCAD can coordinate with Ag⁺ at the air–water surface. Under the optimum experimental conditions, this voltammetric sensor shows a linear voltammetric response for Ag⁺ in the range of 1.0?×?10^?8?～?6.0?×?10^?6?mol?L^?1 with detection limit 5.0?×?10^?9?mol?L^?1. The high sensitivity, selectivity, and stability of this LB film modified electrode also demonstrate its practical application for a simple, rapid and economical determination of Ag⁺ in water sample.     

SYNTHESIS,PROPERTIES AND AN ELECTROACTIVE FILM OF RUTHENIUM(II) COMPLEXES WITH THE PYRIDINE DERIVATIVE LIGAND: trans-[RuCl2(pmp)4].(pmp=3-(PYRROL-1-YLMETHYL)PYRIDINE)

Abstract

In this work we report the synthesis, characterization and electrochemistry of the complex trans-[RuCl₂(pmp)₄], where pmp=3-(pyrrol-l-ylmethyl)pyridine. The complex was characterize by electronic spectroscopy (Λ_max = 404 nm and ε = 27000), vibrational FT-IR spectroscopy, ¹H and ¹³C NMR, showing results typically in agreement with trans geometry. Cyclic voltammetry reveals a redox process centered on the Ru(II) center (E^1/2 = 0.53V vs. NHE), which is electrochemically and chemically reversible. Spectroelectrochemistry shows the progressive disappearance of bands at 404 and 475 nm and the appearance of a new band at 302 nm during the oxidation process. Cyclic voltammetric experiments were performed to characterize the redox properties of the ruthenium complex; its electropolymerization produced a strongly adhesive conducting polymeric film on platinum and palladium electrodes.     

A study of HPLC separation and spectrophotometric, polarographic and voltammetric detection of 4-substituted derivatives of N-nitroso-N-methylaniline

Optimised conditions have been found for the separation of N-nitroso-N-methylaniline derivatives substituted in the position 4 (4-R-NMA, where R =- H,- CH₃, - OCH₃, - Cl, - CN, - OH and - NO₂), using reversed phase HPLC with a C18 chemically bonded stationary phase. Suitable mobile phases are mixtures of aqueous 0.01 mol l^–1 KH₂PO₄ with methanol (4+6) or acetonitrile (7+3), or a mixture of water, methanol, acetonitrile and 80% H₃PO₄ (200+200+200+3). Four detection techniques have been investigated: Direct UV photometry, polarography on a hanging mercury drop electrode, anodic voltammetry on a glassy carbon fibre array electrode and indirect anodic voltammetric detection after photolytic denitrosation of the analytes. The UV photometry is the most universal and yields limits of detection around 10^–6 mol l^–1. Polarography exhibits the poorest sensitivity (with a limit of detection of ca. 10^–5 mol l^–1) but it can be used for selective detection of 4-NO₂-NMA. Direct voltammetric detection is selective for the oxidizable derivatives and the limits of detection attained are lower than those obtained by UV photometry (for 4-OH-NMA) or comparable with (for 4-OCH₃-NMA). When the analytes are photolytically denitrosated to yield oxidizable derivatives, the voltammetric detection of 4-H-NMA, 4-Cl-NMA, 4-CH₃-NMA and 4-NO₂-NMA has limits of detection one order of magnitude lower than those obtained UV photometrically.     

Voltammetric behaviour of hyponitrite ion and its analytical applications

Hyponitrite is electrochemically oxidized at a platinized platinum microelectrode. The overall process is characterized by an appreciable overvoltage; in alkaline solution nitrite and nitrous oxide are the ultimate products. The wave is well shaped and diffusion-controlled, and can be used for the voltammetric determination of microamounts of hyponitrite. Alternatively, the oxidation of hyponitrite by hypochlorite in basic solution can be used for the direct determination of hyponitrite with amperometric end-point detection. The limits of determination of the voltammetric and amperometric methods are about 10^-4 M and 5 · 10^-4 M, respectively.     

L-Cysteine Modified Silver Electrode and Its Application to the Study of the Electrochemistry of Hemoglobin

Abstract

L-cysteine can be modified onto a silver electrode by covalent binding through the sulphur to give very stable and long-lived chemically modified electrodes(CMEs). Hemoglobin(Hb) exhibits an excellent voltammetric response at the resulting CMEs. Linear sweep voltammetric(LSV) measurements of Hb on the CMEs reveal the existence of a linear relationship between the cathodic peak current and the concentration of Hb in the range of 5 X 10^?7 - 1 X 10^?5 mol/L. The detection limit is about 2 X 10^?7 mol/L. The relative standard deviation of results is 4.5% for 10 successive determinations at 2 X 10^?6 mol/L. Other proteins and chemicals present in samples do not interfere in the assay.