A homogeneous dispersion of multiwall carbon nanotubes(MWNT) was achieved by dispersing MWNT into 0.1% Nafion ethanol solution, and a uniform cast film at a glassy carbon electrode(GCE) was obtained via solvent evapor...A homogeneous dispersion of multiwall carbon nanotubes(MWNT) was achieved by dispersing MWNT into 0.1% Nafion ethanol solution, and a uniform cast film at a glassy carbon electrode(GCE) was obtained via solvent evaporation of the MWNT dispersion. A reversible two-electron redox reaction of dopamine was observed at the MWNT-Nafion modified GCE. In comparison with a bare GCE and a Nafion-modified GCE, MWNT-Nafion modified GCE has a higher sensitivity for dopamine. This modified GCE has an excellent selectivity towards dopamine even in the presence of high concentration ascorbic acid(AA) and uric acid(UA) since AA and UA have no observable electrochemical responses at the modified GCE. The electrochemical behavior of dopamine was closely related to the pH of the buffer solution. The oxidation peak current was proportional to the concentration of dopamine over the range from 5×10 -8 to \{1×\}10 -6 mol/L, and a detection limit of 2.5×10 -9 mol/L was obtained after 3 min open-circuit accumulation. The dispersion and morphology of MWNT-Nafion film were investigated by transmission electron microscopy(TEM).展开更多
It is difficult to determine estrogens directly by electrochemical methods because estradiol, estrone and estriol are hydrophobic and electroinactive. Thus, they are only determined by the indirect electrochemical tec...It is difficult to determine estrogens directly by electrochemical methods because estradiol, estrone and estriol are hydrophobic and electroinactive. Thus, they are only determined by the indirect electrochemical techniques. In this paper, based on the voltammetric behavior of estrogens(estradiol, estrone and estriol) on the Nafion\|modified glassy carbon electrode in the presence of CTAB, a novel direct electroanalytical method for the determination of the total amounts of estradiol, estrone and estriol was developed. In pH=8.00 phosphate buffer and in the presence of 6×10\+\{-5\} mol/L CTAB, estradiol, estrone and estriol have very sensitive oxidation peaks at 0.38 V(\%vs\%. SCE) at Nafion\|modified glassy carbon electrode after being accumulated for 3 min at -0.50 V. This peak can be used to determine trace level of estradiol, estrone and estriol. It was found that estradol, estrone and estriol have the similar electrochemical responses on the Nafion\|modified electrode in the presence of other long\|chain cationic surfactants, such as CPB, STAB, CATAB, LTAB. It is observed that the enhancement effect is highest in the presence of CTAB, and the peak current is CTAB concentration\|dependent. However, in the presence of long\|chain anionic surfactants, such as SDBS, and long\|chain nonionic surfactants, such as Triton X\|100, estradiol, estrone and estriol have no voltammetric responses on the Nafion\|modified glassy carbon electrode. The mechanism for the oxidation of estradiol in this system has been discussed, and the reactant site for the oxidation of estradiol has been verified to be the hyrdoxyl group in A\|ring.展开更多
A mercury-free solid electrode system for the electrochemical generation of O ·- 2 was described. The effects of pH, the amount of the surfactant and electrode materials on the reduction of O 2 were investigated....A mercury-free solid electrode system for the electrochemical generation of O ·- 2 was described. The effects of pH, the amount of the surfactant and electrode materials on the reduction of O 2 were investigated. The electrogeneration of O ·- 2 was only obtained at the Pt electrode in this medium system. The different electrochemical behaviour of O 2 at Pt electrode and Au electrode were explained in terms of the different adsorptions of DSAB, which was confirmed by quartz crystal microbalance(QCM). The frequency responses for the reduction of O 2 at Pt electrode and Au electrodes were compared by electrochemical quartz crystal microbalance(EQCM), suggesting that the electrogenerated O ·- 2 was adsorbed on the surface of the Pt electrode. The one-electron reduction of oxygen in this system was also confirmed by using chronocoulometry. The scavenging activities of two kinds of antioxidants(ascorbic acid and cysteine) were examined and compared.展开更多
文摘A homogeneous dispersion of multiwall carbon nanotubes(MWNT) was achieved by dispersing MWNT into 0.1% Nafion ethanol solution, and a uniform cast film at a glassy carbon electrode(GCE) was obtained via solvent evaporation of the MWNT dispersion. A reversible two-electron redox reaction of dopamine was observed at the MWNT-Nafion modified GCE. In comparison with a bare GCE and a Nafion-modified GCE, MWNT-Nafion modified GCE has a higher sensitivity for dopamine. This modified GCE has an excellent selectivity towards dopamine even in the presence of high concentration ascorbic acid(AA) and uric acid(UA) since AA and UA have no observable electrochemical responses at the modified GCE. The electrochemical behavior of dopamine was closely related to the pH of the buffer solution. The oxidation peak current was proportional to the concentration of dopamine over the range from 5×10 -8 to \{1×\}10 -6 mol/L, and a detection limit of 2.5×10 -9 mol/L was obtained after 3 min open-circuit accumulation. The dispersion and morphology of MWNT-Nafion film were investigated by transmission electron microscopy(TEM).
文摘It is difficult to determine estrogens directly by electrochemical methods because estradiol, estrone and estriol are hydrophobic and electroinactive. Thus, they are only determined by the indirect electrochemical techniques. In this paper, based on the voltammetric behavior of estrogens(estradiol, estrone and estriol) on the Nafion\|modified glassy carbon electrode in the presence of CTAB, a novel direct electroanalytical method for the determination of the total amounts of estradiol, estrone and estriol was developed. In pH=8.00 phosphate buffer and in the presence of 6×10\+\{-5\} mol/L CTAB, estradiol, estrone and estriol have very sensitive oxidation peaks at 0.38 V(\%vs\%. SCE) at Nafion\|modified glassy carbon electrode after being accumulated for 3 min at -0.50 V. This peak can be used to determine trace level of estradiol, estrone and estriol. It was found that estradol, estrone and estriol have the similar electrochemical responses on the Nafion\|modified electrode in the presence of other long\|chain cationic surfactants, such as CPB, STAB, CATAB, LTAB. It is observed that the enhancement effect is highest in the presence of CTAB, and the peak current is CTAB concentration\|dependent. However, in the presence of long\|chain anionic surfactants, such as SDBS, and long\|chain nonionic surfactants, such as Triton X\|100, estradiol, estrone and estriol have no voltammetric responses on the Nafion\|modified glassy carbon electrode. The mechanism for the oxidation of estradiol in this system has been discussed, and the reactant site for the oxidation of estradiol has been verified to be the hyrdoxyl group in A\|ring.
文摘A mercury-free solid electrode system for the electrochemical generation of O ·- 2 was described. The effects of pH, the amount of the surfactant and electrode materials on the reduction of O 2 were investigated. The electrogeneration of O ·- 2 was only obtained at the Pt electrode in this medium system. The different electrochemical behaviour of O 2 at Pt electrode and Au electrode were explained in terms of the different adsorptions of DSAB, which was confirmed by quartz crystal microbalance(QCM). The frequency responses for the reduction of O 2 at Pt electrode and Au electrodes were compared by electrochemical quartz crystal microbalance(EQCM), suggesting that the electrogenerated O ·- 2 was adsorbed on the surface of the Pt electrode. The one-electron reduction of oxygen in this system was also confirmed by using chronocoulometry. The scavenging activities of two kinds of antioxidants(ascorbic acid and cysteine) were examined and compared.
