Search

The nanocomposite of Fe2O3-reduced graphene oxide (Fe2O3-RGO) was synthesized by a hydrothermal reduction using self-assembly of Fe(OH)3 colloidal suspension and graphene oxide (GO) as precursors at 180°C. The resulting composites were characterized using XRD, SEM, FTIR, and TGA, and then were used to modify the glassy carbon electrode (GCE). After optimizing the parameters, the electrochemical behavior of honokiol and magnolol on different types of electrode was compared, which indicated that the Fe2O3-RGO composite-modified GCE enhanced electrochemical catalysis effect on the simultaneous determination of honokiol and magnolol. In pH 6.4 PBS solution, two well-shaped oxidation peaks at 0.51 and 0.64 V were observed at the Fe2O3-RGO composite-modified GCE and two well-shaped oxidation peaks were separated absolutely, which eliminated the disturbance between them. A sensitive and simple electrochemical method was proposed for the simultaneous determination of honokiol and magnolol. As to honokiol, the calibration curve is from 1.5 × 10−8 ~ 3.3 × 10−5 M, and the detection limit is 9.64 × 10−9 M. For magnolol, the linear range is from 7.5 × 10−8 ~ 2.6 × 10−5 M, and the detection limit is 1.05 × 10−8 M. [ABSTRACT FROM AUTHOR]

Abstract: WO3 nanowires (nano-WO3) were synthesized using a simple hydrothermal technique, and then used to modify the carbon paste electrode (CPE). The electrochemical behavior of honokiol on the unmodified CPE and nano-WO3 modified CPE was compared. It was found that nano-WO3 remarkably increased the oxidation signal of honokiol. The influences of supporting electrolyte, amount of nano-WO3, accumulation potential and time were studied on the oxidation peak current of honokiol. Based on the strong enhancement effect of nano-WO3, a sensitive, simple and rapid electrochemical method was developed for the detection of honokiol. The linear range was from 3×10−8 to 2.0×10−5 M, and the detection limit was as low as 1×10−8 M after 2-min accumulation. Finally, it was used to determine honokiol in traditional Chinese medicines, and the recovery was over the range between 96.5% and 98.8%. [Copyright &y& Elsevier]

A novel carbon nanotube-modified glassy carbon electrode was described for the direct determination of pyridoxine. The electrochemical behavior of pyridoxine was investigated, and a well-defined oxidation peak with high sensitivity was observed at the modified electrode. Owing to the unique structure and extraordinary properties of multi-wall carbon nanotube (MWNT), the MWNT-modified glassy carbon electrode shows obvious electrocatalytic activity to the oxidation of pyridoxine, since it greatly enhances the oxidation peak current of pyridoxine as well as lowers its oxidation overpotential. Based on this, a very sensitive and simple voltammetric method was developed for the measurement of pyridoxine. A sensitive linear voltammetric response for pyridoxine was obtained in the concentration range of 5 × 10-7–1 × 10-4mol/L, and the detection limit is 2 × 10-7mol/L using differential pulse voltammetry. Compared with other voltammetric methods, this proposed method possesses many advantages such as very low detection limit, fast response, low cost and simplicity. The practical application of this new analytical method was demonstrated with pyridoxine drugs. [Copyright &y& Elsevier]

A novel chemically modified electrode has been prepared on the basis of the attachment of multi-wall carbon nanotubes (MWNT) onto the surface of a glassy carbon electrode (GCE) in the presence of a hydrophobic surfactant, dihexadecyl phosphate (DHP). This MWNT film was characterized by transmission electron microscopy images (TEM) and scanning electron microscopy (SEM). The electrochemical behavior of tyrosine at the MWNT film coated GCE was examined and it is found that this MWNT-modified GCE greatly enhances the oxidation peak current of tyrosine. Effects of some important factors, including pH, scan rate and amount of modifier, on the oxidation process of tyrosine were investigated. When the signal to noise ratio (SNR) is 3, the detection limit is 1 x 10(-7) M. The low relative standard deviations of the detection of tyrosine in human morning urine (3.3%) and white wine (5.2%) suggest a good reproducibility of the modified electrode.

A single-wall carbon nanotubes (SWNT)-film coated glassy carbon electrode (GCE) was described for the determination of tryptophan. In pH 2.5 Na2HPO4-citric acid buffer, tryptophan yields a well-defined and very sensitive oxidation peak at about 1.08 V at the SWNT-film coated GCE. The oxidation peak current increases greatly and the peak potential shifts toward more negative direction at the SWNT-modified GCE in contrast to that at the bare GCE. Under optimized conditions, the oxidation peak current is proportional to the concentration of tryptophan over the range from 4 x 10(-8) to 1 x 10(-5) mol/L. The detection limit is 1 x 10(-8) mol/L at 3 min of accumulation. Using the proposed method, tryptophan in the human's blood serum samples was determined.