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A novel tryptophan-functionalized graphene nanocomposite was employed for the simultaneous determination of hydroquinone and catechol. The analyte electrochemical behavior on the surface of tryptophan-functionalized graphene was investigated by cyclic voltammetry and differential pulse voltammetry. Compared to conventional graphene, enhanced peak currents were obtained that were attributed to the large number of defects on tryptophan-functionalized graphene that accelerated electron transfer between the electrode and analytes. The peak potential difference between hydroquinone and catechol at the tryptophan-functionalized graphene modified glassy carbon electrode was 104 millivolt, which was sufficiently wide to simultaneously determine hydroquinone and catechol. This method was used for the analysis of tap water. [ABSTRACT FROM AUTHOR]

An electrochemical investigation for rutin on glassy carbon electrode is presented. An adsorptive process is observed. The maximum coverage on the electrode surface is 5.09 × 10[sup -10] mol/cm², this area corresponding to a benzene ring with 3',4'-dihydroxides adsorbed on the electrode surface; the other parts of rutin keep away from the surface. In the meantime, a new electrochemical method for determining rutin is presented. In a medium of 0.1 M acetate buffer solution (pH = 4.46), a very sensitive polargraphic adsorptive wave is observed by using a differential pulse voltammetry at about 0.29 V (vs. Ag/AgCl). The linear relationship between the peak current and the concentration of rutin exists in a range from 3.28 × 10[sup -7] to 3.28 × 10[sup -5] M. The detection limit of rutin is down to 2.51 × 10[sup -8] M. This method has been applied to determine rutin in several samples of Chinese medicines. The results are satisfactory. [ABSTRACT FROM AUTHOR]