Sol-gel derived carbon ceramic electrode containing methylene blue-intercalted alpha-zirconium phosphate micro particles

Methylene blue-intercalated a-zirconium phosphate (MBZrP) micro particles in deionized water were deposited onto the surface of graphite powder to prepare graphite powder-supported MBZrP, which was subsequently dispersed into methyltrimethoxysilane-derived gels to yield a conductive composite. The composite was used as electrode material to fabricate a surface-renewable, rigid, leak-free carbon ceramic composite electrode, bulk-modified with methylene blue (MB). In the configuration, alpha-zirconium phosphate was employed as a solid host for MB, which acted as a catalyst. Graphite powder ensured conductivity by percolation, the silicate provided a rigid porous backbone and the methyl groups endowed hydrophobicity and thus limited the wetting section of the modified electrode. Peak currents of the MBZrP-modified electrode were surface-confined at low scan rates but diffusion-controlled at high scan rates. Square-wave voltammetric study revealed that MBZrP immobilized in carbon ceramic matrix presented a two-electron, three-proton redox process in acidic aqueous solution with pH ranged from 0.44 to 2.94. In addition, the chemically modified electrode showed an electrocatalytic activity toward nitrite reduction at +0.15 V (vs. Ag/AgCl) in acidic aqueous solution (pH=0.44). The linear range and detection limit are 1 x 10(-6)-4 x 10(-3) mol L-1 and 1.5 x 10(-7) mol L-1, respectively.

Electrocatalytic oxidation of dopamine by ferrocene in lipid film cast on a glassy carbon electrode

The ferrocene-lipid film electrode was successfully prepared by means of casting the solution of ferrocene and lipid in chloroform onto a glassy carbon (GC) electrode surface. Ferrocene saved in the biological membrane gave a couple of quasi-reversible peaks of cyclic voltammogram. The electrode displays a preferential electrocatalytic oxidation of dopamine (DA). The effect of electroccatalytic oxidation of DA depends on the solution pH and the negative charge lipid is in favor of catalytic oxidation of DA. The characteristic was employed for separating the electrochemical responses of DA and ascorbic acid (AA). The electrode was assessed for the voltammetric differentiation of DA and AA. The measurement of DA can be achieved with differential pulse voltammetry in the, presence of high concentration of AA. The catalytic peak current was proportional to the concentration of DA in the range of 1 x 10(-4)-3 x 10(-3) mol/L.

Preparation and gas sensitivity of octa-n-butoxy-2,3-naphthalocyanine copper(II) Langmuir-Blodgett film

The formation process of monolayer of octa-n-butoxy-2,3-naphthalocyanine copper ( I), [CuNc(OBu)(8)], on water subphase was studied. Its multilayers were successifully deposited on the hydrophilic substrates by Z-type deposition mode using LB technique. Stable solid film with a limiting molecular area of 0.74 nm(2) and a collapse pressure of 55 mN/m were formed. The LB film structure was characterized by IR and electronic absorption spectra. Macrocycle of CuNc (OBu)(8) molecules have a face-to-face arrangement in the multilayers. These films have good sensitivities to vapor of alcohols, with the following sequence of sensitivities: i-PrOH>EtOH>MeOH. The response time and recovery time of the LB films to vapor of MeOH, EtOH and i-PrOH[volume fraction (1-5) X 10(-5)] were within 2 and 5 seconds respectively, while those of the LB films to ammonia(1 X 10(-4)) were 30-60 seconds and 4-5 minutes respectively.

Electrochemiluminescent detection of chlorpromazine by selective preconcentration at a lauric acid-modified carbon paste electrode using tris(2,2 '-bipyridine)ruthenium(II)

A new detection scheme for the determination of adsorbable coreactants of Ru(bpy)(3)(2+) electrochemiluminescent reaction is presented. It is based on selective preconcentration of coreactant onto an electrode, followed by Ru(bpy)(3)(2+) electrochemiluminescent detection. The coreactant employed is chlorpromazine. It was sensitively detected after 5-min preconcentration onto a lauric acid-modified carbon paste electrode. The linear concentration range was found to occur from 1 x 10(-8) to 3 x 10(-6) mol L-1 with a detection limit of 3.1 x 10(-9) mol L-1. The total analysis time is less than 10 min. As a result of selective preconcentration and medium exchange, such remarkable selectivity is achieved that reproducible quantitation of chlorpromazine in urine is possible.

Anodic voltammetric behavior of medecamycin at a glassy carbon electrode

The anodic voltammetric behavior of medecamycin (MD) in the presence of various electrolytes was studied by linearsweep voltammetry, differential-pulse voltammetry and cyclic voltammetry at a glassy carbon electrode. In phosphate buffer solutions (pH = 9.4), MD is oxidized irreversibly. The peak potential is at about +0.75 V (vs.Ag/AgCl). The height of the peak is linearly increased with the concentration of MD over the range of 5 x 10(-5) similar to 1 x 10(-1) g/L. The method has been used for the direct determination of MD in tablets. The relative standard deviation (n = 10) is 1.8%. The recoveries of MD in urine samples are in the range of 95% similar to 115%.

Laser-time-resolved fluorescence spectroscopy in immunoassays

This paper described a laser-excited time-resolved fluoroimmunoassay set. It made lanthanide ion to couple the anhydrde of diethylenetriaminepentaacetic acid (DTPAA) for labeling antibodies. The experiment used polystyrene tap coated with HCV antigen as the solid phase and a chelate of the rare earth metal europium as fluorescent label. A nitrogen laser beam was used to excite the Eu3+ chelates and after 60 ys delay time,the emission fluorescence was measured. Background fluorescence of short lifetimes caused by serum components and Raman scattering can be eliminated by set the delay rime. In the system condition, fluorescent spectra and fluorescent lifetimes of Eu3+ beta-naphthoyltrifluroacetone (NTA) chelates were measured. The fluorescent lifetime value is 650 mu s. The maximum emssion wavelength is 613 nm. The linear range of europium ion concentration is 1 x 10(-7)- 1 x 10(-11) g.mL(-1) and the detection limit is 1 x 10(-13) g.mL(-1). The relative standard deviation of determination ( n = 12) for samples at 0.01 ng.mL(-1) magnitude is 6.4%. Laser-TRFIA was also found to be suitable for diagnosis of HCV. The sensitvity and specificity were comparable to enzyme immunoassay. The result was obtained with laser-TRFIA for 29 human correlated well with enzyme immunoassay.

Electrocatalytic oxidation of ascorbic acid by ferrocene in lipid film cast on a glassy carbon electrode

A ferrocene-dimyristoyl phosphatidylcholine (DMPC) film electrode was prepared by casting the solution of ferrocene and DMPC in chloroform onto a glassy carbon electrode surface. Ferrocene retained in the biological membrane gave a couple of irreversible peaks of cyclic voltammogram. The electrode exhibited good electrocatalytic activity for the oxidation of ascorbic acid (H(2)A) in phosphate buffer (pH 6.64) with an anodic peak potential of +340 mV (vs. Ag/AgCl). The anodic current was directly proportional to the square root of the scan rate below 150 mV s(-1). The influence of the pH value was investigated and it was observed that pH 6.64 was the suitable value to the anodic peak potential and current. The thickness of the film and the interference of uric acid were also studied. The electrode can be used to determine H(2)A in the presence of equimolar uric acid. The catalytic peak current increased linearly with the concentration of H(2)A in the range of 1 X 10(-4)-5 X 10(-3) mol L-1.

Determination of allopurinol and its active metabolite oxypurinol by capillary electrophoresis with end-column amperometric detection

A simple method was proposed for the separation of allopurinol (AP) and its active metabolite oxypurinol (OP) by capillary electrophoresis with end-column amperometric detection. A running buffer composed of 15 rum Na2HPO4/NaH2PO4 at a pH 9.55, electrokinetic injection 7 s at 5 kV, separation voltage at 15 kV and detection potential at 1.20 V were investigated to be the optimal condition for the separation. The method exhibited low detection Emit (S/N = 3) as 1 x 10(-8) mol/l for AP and OP, wide linearity range of 2 x 10(-7) to 1 x 10(-4) mol/l, 1 x 10(-7) to 1 x 10(-4) and high efficiency of 1.2 x 10(5) and 1.8 x 10(5) N/m for AP and OP, respectively. The potential application examined for the method was the determination of the spiked urine sample, which was proved to be sensitive and efficient. (C) 2001 Elsevier Science B.V. All rights reserved.

New microsystem of capillary electrophoresis with amperometric detection

We have made a cheap microsystem of capillary electrophoresis with a new method, integrating the electrodes, injection channel, separation channel, buffer reservoirs and detection cell on a polymethylmethacrylate (PMMA) chip. Using an integrated micro carbon fiber disk electrode as the working electrode in three electrodes system, 1 x 10(-4) mol/L dopamine(DA) could be detected with end-column amperometric detection. The reproducibility was good. Peak current was 6.73 nA,theoretical plate number was 71300/m and height equivalent of one theoretical plate height was 14.0 mum for 1 x 10(-4) mol/L DA. The limit of detection was 3.6 x 10(-8) mol/L and the linear range was extended from 5 x 10(-7) mol/L to 1 x 10(-4) mol/L for DA. 1 x 10(-4) mol/L catechol (CA) and 5 x 10(-5) mol/L DA were also separated completely with R-s = 10.1.

新型无机-有机杂化中孔发光材料(phen)_2Eu/MCM-41的合成与表征

合成出了担载稀土有机配合物的无机 -有机杂化中孔发光材料 ( phen) 2 Eu/MCM-4 1 ,用 X射线衍射、红外光谱、荧光光谱和紫外 -可见漫反射光谱对所得样品进行了表征 ,并与相应的纯稀土配合物进行了比较 .结果表明 ,所得杂化材料具有典型的中孔材料 MCM-4 1的结构 ,且经组装后孔结构保持不变 ,在紫外光照射下 ,发出稀土离子的特征谱线 ,但与纯稀土配合物相比 ,其激发光谱发生蓝移 ,稀土 Eu3+ 所处的格位对称性降低 ,荧光寿命延长 .另外 ,对光谱性质进行了讨论 .

End-column amperometric detection of 6-mercaptopurine by capillary zone electrophoresis

End-column amperometric detection of 6-mercaptopurine by capillary zone electrophoresis was described with high resolution and speed. The detection conditions were optimized and the electrochemical behavior was observed. Under the optimal conditions: detection potential of 1.2 V ( vs. Ag/AgCl), operating voltage of 15 kV, sample injection of 3 s at 15 kV and 10 mmol/l Na2HPO4 buffer, the detection limit for 6-MP was as low as 1 x 10(-7) mol/L and the linear range was from 5 x 10(-4) to 5 x 10(-6) mol/L with the relative coefficient of 0.995. The RSD of reproducibility for peak current and migration time was 2.5% and 1.2%, respectively. This method was utilized in assay real sample of human mine and bovine serum albumin containing 6-mercaptopurine.

Voltammetric behavior of tetracine on glassy garbon electrode and its application

The anodic voltammetric behavior of anaesthetic tetracine and its application were studied. In 0.1 mol/L HClO4 solution, the potential of anodic peak for tetracine is 1.04 V(vs. Ag/AgCl) at a glassy carbon electrode. A linear relationship between the peak height and the concentration of tetracine in the range of 5 x 10(-4) similar to 1 x 10(-1) g/L was obtained. The peak current decreases with the decreasing acidity of the solution. the mehtod has been used for the direct determination of tetracine in injections. The average recoveries of tetracine in urine samples were 98.5%. The mechanism of the electrode reaction was also discussed.

In-situ circular dichroism spectroelectrochemical study on the redox process of norepinephrine

The redox process of norepinephrine in pH = 7.0 phosphate buffer solution at glassy carbon electrode was studied by circular dichroism spectroelectrochemistry with a long optical path thin layer cell. The spectroelectrochemical data were analyzed with the double logarithm method. According to the double logarithsmic plot results, the mechanism of electrochemical oxidation of norepinephrine is an irreversible process with a subsequent chemical reaction (EC) to form a norepinephrinechrome. Both of norepinephrinequinone and norepinephrinechrome are followed E mechanisms. Some kinetic parameters about the electrochemical process, i.e. the electron transfer coefficient and number of electron transfered, alpha n = 0.38, the formal potential, E-1(0)' = 0.20 V, the standard heterogenous electron transfer rate constant, k(1)(0) = 1.2 x 10(-4) cm s(-1) for the oxidation of norepinephrine, alpha n = 0.37, E-2(0)' = 0.25 V and k(2)(0) = 4.4 x 10(-5) cm . s(-1) for the reduction of norepinephrinequnone and alpha n = 0.33, E-3(0)' = -0.25V and k(3)(0) = 1.1 x 10(-4) cm . s(-1) for the reduction of norpinephrinechrome, were also estimated.

Determination of electron mobility in a blue-emitting alternating block copolymer by space-charge-limited current measurements

In this communication we analyse current versus voltage data obtained using one carrier injection at metal/polymer/metal structures, The used polymer is a soluble blue-emitting alternating block copolymer, Our experimental results demonstrate that the electron current is limited by a large amount of traps with exponential energy distribution in the copolymer. The electron ;mobility of 5.1 x 10(-10) cm(2)/V s is directly determined by space-charge-limited current measurements. The electron mobility is at least three orders of magnitude smaller than that for holes in the copolymer. (C) 1999 Elsevier Science Ltd. All rights reserved.

Sol-gel synthesis and electrical properties of ceria-based solid electrolytes

A series of solid electrolytes (Ce0.8RE0.2)(1-x)MxO2-delta(RE: Rare earth, M: Alkali earth) were prepared by sol-gel methods. XRD indicated that a pure fluorite phase was formed at 800 degrees C. The synthesis temperature by the sol-gel methods was about 700 degrees C lower than by the traditional ceramic method. The electrical conductivity and impedance spectra were measured. XPS showed that the oxygen vacancy increased obviously by doping MO, thus, resulting in the increase of the oxygen ionic transport number and conductivity. The performance of ceria-based solid electrolyte was improved. The effects of RE2O3 and MO on the electrical properties were discussed. The conductivity and the oxygen ionic transport number of (Ce0.8Sm0.2)(1-0.05)Ca0.05O2-delta is 0.126 S.cm(-1) and 0.99 at 800 degrees C, respectively.