Amperometric determination of ascorbic acid at a novel ‘self-doped’ polyaniline modified microelectrode

A ‘self-doped’ polyaniline modified microelectrode, prepared by cyclic potential sweep on a microdisk gold electrode from –0.2 to 0.85 V in 0.5 mol/L sulfuric acid containing aniline and o-aminobenzoic acid, has been developed. The copolymerized process and the resulting polymer characteristics were investigated in detail. This composite film indicated a good electrochemical activity in a wide pH range even in basic solution. Meanwhile, the redox couple exhibited an excellent electrocatalytic activity for the oxidation of ascorbic acid. The oxidation overpotential of ascorbic acid was decreased over 200 mV at this modified electrode compared with a bare gold one. Moreover, the effects of film thickness and pH on the catalytic efficiency were further studied. The dependence of catalytic currents on the concentration of ascorbic acid was linear in the range of 1.2 × 10^–5～ 2.4 × 10^–3 mol/L with a correlation coefficient of 0.996. Also, the determination of ascorbic acid in actual samples was evaluated and the results are satisfactory.     

Synthesis and structure of a novel three-dimensional metal selenite containing multidirectional intersecting double helical chains: [Fe2(H2O)4(SeO3)2]

A novel three-dimensional metal selenite [Fe₂(H₂O)₄(SeO₃)₂] (1) has been hydrothermally synthesized and characterized by the elemental analyses, IR spectrum, TG analysis and the single crystal X-ray diffraction. Compound 1 crystallizes in the monoclinic system, space group P21/n, with a=6.5283(13) Å, b=8.8754(18) Å, c=7.6798(15) Å, (=98.82(3)β, V=439.71(15) Å3, and Z=2. Compounds 1 exhibits interesting three-dimensional structure constructed from {FeO₆} octahedra and {SeO₃} pyramids linked via the corner- and/or edge-sharing mode. The most interesting structural feature of compound 1 is that the existence of multidirectional intersecting double helical chains in one compound.     

Electrochemical determination of iodide on a vanadium oxide-polypropylene carbonate coated glassy carbon electrode

A vanadium oxide-modified glassy carbon electrode was simply and conveniently fabricated by casting vanadium tri(isoproxide) oxide (VO(OC₃H₇)₃) and poly(propylene carbonate) (PPC) onto the glassy carbon electrode surface. The electrochemical properties of iodide at the VO(OC₃H₇)₃-PPC film-modified glassy carbon electrode were investigated by cyclic voltammetry, and an anodic peak was observed at approximately +0.71 V (vs. SCE). Based on this, a sensitive and convenient electrochemical method was proposed for the determination of iodide. Flow injection amperometry (FIA) exhibited a good linear relationship with the concentration of iodide in the range of 5 × 10⁻⁷ mol L⁻¹ and 1 × 10⁻³ mol L⁻¹, and the detection limit was 1 × 10⁻⁷ mol L⁻¹. Quantitative recovery of iodide in synthetic samples has been obtained and the interferences from different cations and anions have been studied. The method has been successfully applied to the determination of iodide in dry edible seaweed. The concentrations of iodide measured by this method are in good agreement with those obtained by spectrophotometric method.     

Effect of solvent composition on free release static coating of capillary columns

Summary Three aspects with respect to the selection of solvents for static coating of capillary columns, i.e. coating speed, occurrence of bumping and solubility of stationary phases are discussed. Hypotheses are proposed in an attempt to explain the observed facts that mixed solvents result in much higher coating speeds than those obtained from pure solvents, that a proper choice of solvents together with a good and uniform deactivitation of the column inner wall is needed to prevent bumping. Stationary phase solubility vs. solvent composition is also briefly discussed.     

Synthesis and magnetic properties of the one-dimensional linear chain structure cyano-bridged complex [Cu(teta)(H2O)2][Cu(teta) Fe(CN)6]ClO4·2H2O (teta=5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacylotetradecane)

Reaction of either K₃[Fe(CN)₆] or K₄[Fe(CN)₆] with a macrocyclic Cu^II complex, [Cu(teta)](ClO₄)₂ (teta = 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacylotetradecane), in aqueous solution gave the same product as shown by spectroscopic and physicochemical characterisation. The crystal structure of the complex shows that it is a one-dimensional linear chain type heterobinuclear Fe^III–Cu^II polymer. The unit is composed of a [Cu(teta)(H₂O)₂]²⁺ cationic complex, a Fe^III–Cu^II alternate linear chain unit, a ClO ₄ ^– ion and four water molecules. The Cu atom is coordinated in a distorted octahedral arrangement by four nitrogen atoms from one teta ligand and two nitrogen atoms of the bridging cyanide groups. The Cu—N bond distances involving the cyanide bridges, 2.522(7) and 2.608(7)Å, respectively, indicate weak antiferromagnetic interactions between the Fe^III and Cu^II atoms.     

Comparison of conventional and enhanced mass resolution triple-quadrupole mass spectrometers for discovery bioanalytical applications

A new triple-quadrupole mass spectrometry (MS) system with enhanced resolution capabilities has recently become available. In order to evaluate the performance of this new instrument for drug discovery assays, both the linearity and the limit of detection were compared in the positive electrospray ionization (ESI) mode with those of a conventional triple-quadrupole instrument supplied by the same manufacturer. For these studies, spiked mouse plasma standard samples were split and assayed by each instrument, which allowed for a direct comparison of the two systems. In the unit mass resolution mode, the new mass spectrometer was found to be at least ten-fold more sensitive than the conventional instrument. The sensitivity of the new mass spectrometer under the enhanced mass resolution mode was found to be even better by another factor of two. For the test compound, the linear dynamic range was found to be 0.05-5000 ng/mL for the new instrument as compared with 2.5-5000 ng/mL for the conventional mass spectrometer.     

Electron momentum spectroscopy of CF2Cl2: experimental and theoretical momentum profiles for outer valence orbitals

Electron momentum distributions for outer valence orbitals of CF2Cl2 have been obtained by (e,2e) electron momentum spectroscopy at an incident energy of 1200 eV + binding energy. The experimental electron momentum profiles are compared with Hartree-Fock and density functional theory (DFT) calculations using B3LYP hybrid functional with the 6-31G and 6-311+G* basis sets. Generally, the shapes of the experimental momentum profiles are well reproduced by DFT calculations using larger basis sets 6-311 + G*. An attempt has been made to clarify the ordering of the outer valence orbitals, which have been in controversy, by comparing experimental results with B3LYP/6-311 + G* calculations.     

Direct STM investigation of cinchona alkaloid adsorption on Cu(III)

Scanning tunneling microscopy (STM) combined with cyclic voltammetry has been employed to investigate the adsorption of cinchonine on Cu(111). Similar to cinchonidine, cinchonine forms a long-range ordered adlayer with (4 x 4) symmetry on the substrate. The structural details on molecular adsorption were obtained by high-resolution STM images. On the basis of the previous results and obtained STM images, the quinoline ring is proposed to lie parallel to Cu(111) and serve as an anchoring group. The chiral quinuclidine moiety extends out of the surface to facilitate the interaction with the prochiral reactants.     

Curing behavior and toughening performance of epoxy resins containing hyperbranched polyester

The effects of the hyperbranched polyester with hydroxyl end groups (HBPE‐OH) on the curing behavior and toughening performance of a commercial epoxy resin (diglycidyl ether of bisphenol A, DGEBA) were presented. The addition of HBPE‐OH into DGEBA strongly increased its curing rate and conversion of epoxide group due to the catalytic effect of hydroxyl groups in HBPE‐OH and the low viscosity of the blend at curing temperature. The improvements on impact strength and critical stress intensity factor (or fracture toughness, K_1c) were observed with adding HBPE‐OH. The impact strength was 8.04 kJ m^?1 when HBPE‐OH reached 15 wt% and the K_1c value was approximately two times the value of pure epoxy resin when HBPE‐OH content was 20 wt%. The morphology of the blends was also investigated, which indicated that HBPE‐OH particles, as a second phase in the epoxy matrix, combined with each other as the concentration of HBPE‐OH increased. Copyright © 2004 John Wiley & Sons, Ltd.     

一种用于版权保护的随机相位量化编码方法

基于传统的随机相位编码技术，提出了一种新的相息图量化编码方法。该方法采用条码编码技术和数制转换原理，将编码得到相息图的高阶量化信息映射为二值矩阵，并进一步打印制作成二值的防伪标签，不但可以实现文本内容的自动录入，同时也提高了传统随机相位编码技术解码图像的信噪比。计算机仿真与光学扫描实验表明，该方法具有认证过程相对简单、解码图像信噪比高、成本低和防伪性能好等优点。