Chemiluminescence determination of trace ascorbic acid with chromium (VI)-H2O2-luminol system

A new chemiluminescence(CL) system for the determination of ascorbic acid has been established. By the fast reduction reaction between chromium(VI) and ascorbic acid, chromium(M was generated to react with luminol and hydrogen peroxide in alkaline aqueous solution and hydrogen peroxide to produce CL. The CL emission intensity was correlated with ascorbic acid concentration in the range 8.0 x 10(-9) to 1.6 x 10(-4) mol/L, and the detection limit was 8.0 x 10(-9) mol/L ascorbic acid. The relative standard deviation (n = 11) for 1.0 x 10(-6) mol/L ascorbic acid is 0.9%. The method has been applied to the determination of ascorbic acid in vitamin C tablets with satisfactory results.

Studied on the interactions of antibody-porphyrin by circular dichroism and ultraviolet-visible spectrophotometry

Circular dichoism and UV-vis measurements were used to study the interaction between porphyrin and monoclonal antibodies ( McAbs). McAbs-porphyrin complex formation is usually accompanied by significant bathochromic shift and hyperchromicity changes of the absorption maxima in the porphyrin soret band region. Induced CD spectra in the same region (350 similar to 450 nm) were detected upon complex formation. They follow Lamb-Beer's law and exhibit isosbestic behavior. Both the UV-Vis and induced CD spectra of the antibody: porphyrin complex remain unchanged over a broad pH range ( pH 6 similar to 11), indicating remarkable stability of the complex and reflecting the dominant role of hydrophobic interaction between the hapten benzophenone and the antibody combining site.

Rapid molecular weight determination of recombinant hirudin by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

The molecular weight of recombinant hirudin ( rHV-2) was determined rapidly by matrix-assisted laser desorption/ionization time of fight mass spectrometry (MALDI-TOF-MS). The effects of the three types of matrixes were compared and discussed, alpha-cynao-4-hydroxycinnamic acid was proved to be the best matrix. It showed that MALDI-TOF-MS was superior to the traditional method of molecular weight determination of the biological macromolecules. The mass spectrum data proved that the primary structure of rHV-2 was correct and there was no amino acid deletion, mutation and modification in its expression, refolding and purification.

Determination of the interfacial acidity of the functional alkanethiols self-assembly membrane by capacitance measurement

The acid-base equilibrium of self-assembly monolayer(SAM) of mercaptopropionic acid on gold electrode was studied by capacitance titration. The change of capacitance was due to protonation and deprotonation of the modified electrode surface. This method can be used to measure pH value in solution and capacitance of solid/liquid on SAMs surface synchronously. The shift of pK(a) was observed during the experiment as previous reports. The factors that affect the capacitance measurement were discussed in detail.

A method to construct a third-generation horseradish peroxidase biosensor: Self-assembling gold nanoparticles to three-dimensional sol-gel network

A novel method for fabrication of horseradish peroxidase biosensor has been developed by self-assembling gold nanoparticles to a thiol-containing sol-gel network. A cleaned gold electrode was first immersed in a hydrolyzed (3-mercaptopropyl)-trimethoxysilane (MPS) sol-gel solution to assemble three-dimensional silica gel, and then gold nanoparticles were chemisorbed onto the thiol groups of the sol-gel network. Finally, horseradish peroxidase (HRP) was adsorbed onto the surface of the gold nanoparticles. The distribution of gold nanoparticles and HRP was examined by atomic force microscopy (AFM). The immobilized horseradish peroxidase exhibited direct electrochemical behavior toward the reduction of hydrogen peroxide. The performance and factors influencing the performance of the resulting biosensor were studied in detail. The resulting biosensor exhibited fast amperometric response (2.5 s) to H2O2. The detection limit of the biosensor was 2.0 mumol L-1, and the linear range was from 5.0 mumol L-1 to 10.0 mmol L-1. Moreover, the studied biosensor exhibited high sensitivity, good reproducibility, and long-term stability.

Application of modified Nafion membrane to the sulfur dioxide gas electrochemical sensor

The electrochemical SO2 sensor worked at the fixed potential and prepared with Nafion membrane as the solid electrolyte was studied. It v as observed that after Nafion membrane, was treated with H2SO4, the water-preserving ability of the membrane was increased. In turn, the performance of the sensor became stable. After lifetime test for 4 months, the performance of the sensor deceased slightly, Thus this kind of sensor may become a gas sensor for the practical application.

Progress in deoxyribonucleic acid electroanalysis

The electroanalysis research of deoxyribonucleic acid (DNA) is an attractive project in life science. This paper reviews the recent progress of DNA electrochemical analysis, which includes DNA electroanalysis and DNA electrochemical biosensors. The prospects of the research are very bright. 77 papers are cited.

Study of electron transfer across the liquid/ice-like matrix interface by scanning electrochemical microscopy

In this work, we report the findings of a study on scanning electrochemical microscopy (SECM) to investigate the interfacial electron-transfer (ET) reaction between the 7,7,8,8-tetracyanoquinodimethane radical anion (TCNQ(.-)) in 1,2-dichloroethane and ferricyanide in an ice-like matrix (a mixture of insulting ice and conductive liquid) under low temperatures. Experimental results indicate that the formed liquid/ice-like matrix interface is superficially similar in electrochemical characteristics to a liquid/liquid interface at temperatures above -20 degreesC. Furthermore, imaging data show that the surface of the ice-like matrix is microscopically flat and physically stable and can be applied as either a conductive or an insulting substrate for SECM studies. Perchlorate ion was selected as the common ion in both phases, the concentrations of which controlled the interfacial potential difference. The effect of perchlorate concentration in the DCE phase on interfacial reactions has been studied in detail. The apparent heterogeneous rate constants for TCNQ(.-) oxidation by Fe(CN)(6)(3-) in another phase under different temperatures have been calculated by a best-fit analysis, where the experimental approach curves are compared with the theoretically derived relationships. Reaction rate data obey Butler-Volmer formulation before and after the freezing point, which is similar to most other known cases of ET reactions at liquid/liquid interfaces. However, there is a sharp change observed for heterogeneous rate constants around the freezing point of the aqueous phase, which reflects the phase transition. At temperatures below -20 degreesC, surface-confined voltammograms for the reduction of ferricyanide were obtained, and the ice-like matrix became an insulating one, which indicates that the aqueous phase is really a frozen phase.

Multilayer assembly of Bis-Keggin-type heteropoly compound on chemically modified glassy carbon electrode and its electrocatalysis

Through layer-by-layer assembly, the bis-Keggin-type heteropolyanion K10H3 [Nd(SiMo7W4O39)(2)] XH2O was successfully immobilized on a glassy carbon electrode surface grafted covalently by 4-aminobenzoic acid. The electrochemical behavior of the heteropolyanion was investigated. Cyclic voltammetry proved the uniform growth of the film. However, the characteristic redox peaks of the heteropolyanion in the film were deformed with increasing of the number of the multilayer film. The effect of pH on the redox behaviors of [Nd(SiMo7W4)(2)](13-) in the film was discussed. The multilayer film electrodes have excellent electrocatalytic activities to the reduction of BrO3-, HNO2 and H2O2.

Conductive behavior and ionic conductivity of composite polymer electrolytes

The ac impedance plots of ( PEO)(16) LiClO4-EC composite polymer electrolytes were studied. The equivalent circuit of stainless steel electrode(SS)/composite electrolyte/SS system was applied to explain the ac impedance plots, The results showed that the equivalent circuit could fit the experimental data very well. The ionic conductivity was calculated using the bulk resistance that was obtained from equivalent circuit. The effect of EC on the conductive behavior was explained by the interactions among different species formed in the composite polymer electrolytes. For lower EC concentration samples, the temperature dependence of conductivity in low temperature range followed Arrhenius type, but when EC concentration was larger than 20%, the temperature dependence of conductivity obeyed the Vogel-Tamman-Fulcher (VTF) equation in all temperature ranges.

Anodic voltammetric behavior of ethacridine at a glassy carbon electrode

The anodic voltammetric behavior of ethacridine (EAD) in the presence of various electrolytes was studied by using linear potential sweep voltammetry, differential-pulse voltammetry and cyclic voltammetry at a glassy carbon electrode. In the medium of 0.1 mol/L NaOH solution, an oxidative peak of ethaeridine was obtained. The peak potential is at about 0.40 V (vs. Ag/AgCl). The peak current is linearly increased with the concentration of ethaeridine over the range of 0.05 similar to 80 mg/L. The method has been used for the direct determination of ethacridine in injection. The relative standard deviation (n = 10) is 1.4% similar to 2.7%. The recoveries of ethacridine in urine samples are 89% similar to 95%. The mechanism of the electrode reaction was also discussed.

Investigation of ion transfer across the micro-water/nitrobenzene interface facilitated by a fullerene derivative

A functionalized fullerene derivative containing a monoaza-18-crown-6 moiety was investigated by facilitated ion (such as Li+, Na+, K+, NH4+, Mg2+, and Ca2+) transfer across the micro-water/nitrobenzene interface supported at the tip of a micropipet. The current responses were detected by cyclic voltammetry and Osteryoung square wave voltammetry, which demonstrated that the facilitated ion transfer does occur by an interfacial complexation-dissociation process. The diffusion coefficient of this compound in nitrobenzene was approximately (5.90 +/- 0.04) x 10(-7) cm(2) s(-1), which is 1 order of magnitude less than other common ionophores due to the large size of the molecule. The selectivity of this molecule toward the metal ions followed the sequence Na+ > Li+ > K+ > NH4+ > Ca2+ similar to Mg2+. In addition, this compound was also easy to form film at the water/nitrobenzene interface to inhibit the simple ion transfer of tetramethylammonium ion. However, the adsorption of this ionophore has less influence on the facilitated metal ion transfer.

Effect of rare earth element on the metabolism in rats by high resolution proton nuclear magnetic resonance spectroscopy

The high-field nuclear magnetic resonance (NMR) spectra can be used for the rapid multicomponent analysis in small amounts of biological fluids. In this paper, the effect of La (NO3)(3) on the rats' metabolism in urine was investigated by H-1 NMR analysis. The experimental groups of wistar rats were injected intraperitoneally with La(NO3)(3) at doses of 0.2, 2.0, 10 and 20mg/kg body weight. The remarkable variation of low molecular weight metabolites in urine has been identified by H-1 NMR spectra, in which dimethylamine, N, N-dimethylglycine, urea, alpha -ketoglutarate, trimethylamine N-oxide, succinate, citrate and amino acids have been suggested as NMR markers for renal damage and ethanol, lactate, taurine as the markers for liver damage. This work may assess its possible use in the early detection of biochemical changes associated with Rare Earth induced kidney and liver dysfunction.

Matrix effects in flow injection-inductively coupled plasma mass spectrometry

Matrix effects in now injection (FI) inductively coupled plasma mass spectrometry has been studied,and the results have been compared with those of continuous nebulization. The matrix element As and nu with higher ionization potential ( > 9eV) have enhancement effect on the analyte signal,and the heavier the analyte mass, the smaller the enhancement effects by Fl. The matrix elements Cu, In, Li, Na and Pb with lower ionization potential have suppression effect on the analyte signal. The heavier the matrix element mass, the more severe the suppression effects. The heavier the analyte mass, the smaller the suppression effects. The higher ionization potential of analyte, the more severe the suppression effects. Compared with continuous nebulization, the degree of suppression effect is smaller and the degree of the enhancement effect is larger by Fl.

Determination of ascorbic acid by flow injection chemiluminescence suppression method

chemiluminescence suppression method for the determination of ascorbic acid based on Luminol-KIO4-H2O2-ascorbic acid system was established. The linear range for ascorbic acid is 1.0 x 10(-7) similar to 1.0 x 10(-5) mol/L and the detection limit is 6.0 x 10(-8) mol/L. The relative standard deviation (n = 11) is 1.0% for 8.0 x 10(-7) mol/L ascorbic acid. The method has been used to determine the content of ascorbic acid in tablets and injections with satisfactory results.