A NEW TYPE OF ION-SELECTIVE ELECTRODE FOR NONAQUEOUS SOLUTION

A new type of ion-selective electrode-water membrane system is proposed and an assumption of water membrane is confirmed. A NdCl_3 water membrane electrode has be- en made te demonstrate its applicability to the determination of Nd (PMBP)_3 (PMBP=1- phenyl-3-methyl-4-benzoyl-5-pyrazolone)in cyclohexanone. Conditions for stabilizing potential of reference electrode in nonaqueous system are optimized. It is observed that the potential response on the surface of two immiscible solution is bidirection...

INVESTIGATION OF MICROSTRUCTURE AT IRON TETRAPHENYLPORPHYRIN MODIFIED CLASSY CARBON ELECTRODE BY XPS

Microstructure of the glassy carbon surface modified with iron tetraphenyfporphyrin (FeTPP) by heat treatment has been studied by XPS,, DTA and TG. XPS spectra of Fe 2P_3\2 level in FeTPP and iron tetraphenylporphyriu/glassy carbon (FeTPP/GC) have shown that a bond can be formed between the glassy carbon surface and both the central metal iron ion and the macrocyclic, ligand, which loses its four phenyl groups during the beat treatment. The relationship between the surface mierostructure of FeTPP/GC and the...

An electrochemical DNA sensor based on electrodepositing aluminum ion films on stearic acid-modified carbon paste electrode and its application for the detection of specific sequences related to bar gene and CP4 Epsps gene

An electrochemical DNA biosensor was fabricated by immobilizing DNA probe on aluminum ion films that were electrodeposited on the surface of the stearic acid-modified carbon paste electrode (CPE). DNA immobilization and hybridization were characterized with cyclic voltammetry (CV) by using methylene blue (MB) as indicator. MB has a couple of well-defined voltammetric redox peaks at the CPE. The currents of redox peaks of MB decreased after depositing aluminum ion films on the CPE (Al(III)/CPE) and increased dramatically after immobilizing DNA probe (ssDNA/Al(III)/CPE). Hybridization of DNA probe led to a marked decrease of the peak currents of MB, which can be used to detect the target single-stranded DNA. The conditions for the preparation of Al(III)/CPE, and DNA immobilization and hybridization were optimized. The specific sequences related to bar transgene in the transgenic corn and the PCR amplification of CP4 epsps gene from the sample of transgenic roundup ready soybean were detected by differential pulse voltammetry (DPV) with this new electrochemical DNA biosensor. The difference between the peak currents of MB at ssDNA/Al(III)/CPE and that at hybridization DNA modified electrode (dsDNA/Al(III)/CPE) was applied to determine the Specific sequence related to the target bar gene with the dynamic range comprised between 1.0 X 10(-7) mol/L to 1.0 x 10(-4) mol/L. A detection limit of 2.25 x.10(-8) mol/L. of oligonucleotides can be estimated.

Preparation of porous chitosan/agarose microsphere and its R-phycoerythrin release properties

The chitosan microspheres (CS-CL) were prepared by suspension crosslinking method and used as carriers of R-phycoerythrin (R-PE). In this study, R-PE was loaded in the microspheres and released in vitro. The effects of pH value, temperature, ionic strength, and R-PE concentration on loading efficiency and release behavior were discussed. A novel microsphere that contained agarose (CS-AR MP) was prepared and the basic loading and releasing behavior for R-PE of this kind of new micro-spheres were also investigated. The results showed that all these chitosan microspheres have the ability to control-release R-PE. The addition of agarose may somewhat accelerate the release rate of R-PE from microspheres and reduce the capacity of adsorption for R-PE. (c) 2006 Wiley Periodicals, Inc.

Fabrication of Bismuth/Multi-walled Carbon Nanotube Composite Modified Glassy Carbon Electrode for Determination of Cobalt

A bismuth/multi-walled carbon nanotube (Bi/MWNT) composite modified electrode for determination of cobalt by differential pulse adsorptive cathodic stripping voltammetry is described. The electrode is fabricated by potentiostatic pre-plating bismuth film on an MWNT modified glassy carbon (GC) electrode. The Bi/MWNT composite modified electrode exhibits enhanced sensitivity for cobalt detection as compared with the bare GC, MWNT modified and bismuth film electrodes. Numerous key experimental parameters have been examined for optimum analytical performance of the proposed electrode. With an adsorptive accumulation of the Co(II)-dimethylglyoxime complex at -0.8 V for 200 s, the reduction peak current is proportional to the concentration of cobalt in the range of 4.0x10(-11)-1.0x10(-7) mol/L with a lower detection limit of 8.1x10(-11) mol/L. The proposed method has been applied Successfully to cobalt determination in seawater and lake water samples.

Ionophore Based Bismuth Film Electrode for Lead

A Nafion/ionophore, 4-tert-butylcalix[4]arene-tetrakis(N,N-dimethylthioacetamide) composite coated and bismuth film modified glassy carbon electrode. (GC/NA-IONO/BiFE) was described to determine trace lead sensitively and selectively. The characteristics of such modified GC/NA-IONO/BiFE were studied by scanning electron microscopy and cyclic voltammetry. The influence of various experimental parameters upon the stripping lead signal at the GC/NA-IONO/BiFE was explored. Under the optimized conditions, the differential pulse voltammetric stripping response is highly linear over the 0.1-8.0 nM lead range examined (180s preconcentration at -1.2V), with a detection limit of 0.044nM and good precision (RSD=5.4% at 0.5nM). Also applicability to seawater samples was demonstrated at such modified electrode. The high selectivity of ionophore coupled with the excellent electrochemical characteristics of bismuth endow the GC/NA-IONO/BiFE a promising and robust tool for monitoring of trace lead rapidly and precisely.

Influence of electrode structure on the performance of a direct methanol fuel cell

Direct methanol fuel cells (DMFCs) consisting of multi-layer electrodes provide higher performance than those with the traditional electrode. The new electrode structure includes a hydrophilic thin film and a traditional catalyst layer. A decal transfer method was used to apply the thin film to the Nafion(R) membrane. Results show that the performance of a cell with the hydrophilic thin film is obviously enhanced. A cell with the optimal thin film electrode structure operating at I M CH3OH, 2 atm oxygen and 90degreesC yields a current density of 100 mA/cm(2) at 0.53 V cell voltage. The peak power density is 120 mW/cm(2). The performance stability of a cell in a short-term life operation was also increased when the hydrophilic thin film was employed. (C) 2002 Elsevier Science B.V. All rights reserved.

Fast analysis of capillary electrochromatography with non-porous ODS as the stationary phase

High-speed capillary electrochromatography was developed on both short and long packed columns with 2 mu m non-porous ODS as the stationary phase. Factors that affect the analysis time of samples, such as voltage, electrolyte concentration, pH and organic modifier concentration in the mobile phase, were studied systematically. Fast analysis of aromatic compounds within 13 seconds was realized with column efficiency of 573,000 plates/m and a R.S.D.% of the retention times of all components in 8 consecutive injections below 1.0%. which demonstrated the high efficiency and high reproducibility of such a technique. In addition, DNPH derived aldehydes and ketones in both standards and environmental samples were separated with high speed.