| Carbon nanotubes (CNTs) are tube-like nanoscale fibers composed totally of carbon. Since their discovery in 1991, CNTs have become the subject of intense investigations in chemical, physical, and material area due to their novel mechanical, electronic, and chemical properties. As new nanomaterials, CNTs display high electrical conductivity, high chemical stability, and extremely high mechanical strength and modulus. CNTs modified electrodes can promote the electron transfer of some biomolecules. In this work, CNTs (including SWNT and MWNT) modified Au electrodes were used to study the electrochemical behaviors of several bimolecular, and voltammetric methods for their determination were proposed. The work were summarized as follows:(1) The voltammetric behavior of uric acid (UA) was studied at a single-walled carbon nanotubes (SWNT) modified gold electrode. Uric acid can effectively accumulate at this electrode and produce one anodic peak at about 0.45 V (vs. SCE) in acetate buffer solution (HAc-NaAc pH 5.0). The experimental parameters such as solution pH, accumulation time, and amount of SWNT were optimized for determination. Under the optimum conditions, the anodic peak current is linear to uric acid concentration over the range of 1.0×10-7 mol L-1 to 2.5×10-5 mol L-1 with correlation coefficient of 0.998. The detection limit was 5.0×10-8 mol L-1 for 60s accumulation. The electrode could be easily regenerated and exhibited good stability. A 5.0×10-6 mol L-1 solution was measured for ten times using the same electrode, and the relative standard deviation of the peak current was 1.3%. This method was successfully applied to the determination of uric acid in human urine sample and the recovery was 97.7-99.7 %. The feasibility for simultaneous determination of xanthine (XA), ascorbic acid (AA) and uric acid was discussed. They did not interfere each other in certain concentration range. The influence of some surfactants on the anodic peak of UA was also examined.(2) The voltammetric behavior of folic acid (FA) at a multi-walled carbon nanotubes modified gold electrode was investigated by cyclic voltammetry, chronoamperometry, and chronocoulometry. The modified electrode exhibited good promotion to the electrochemical reaction of FA. At the modified electrode FA can generate a well-defined oxidation peak at about 0.83 V in 0.1 mol L-1 H3PO4-NaH2PO4 solution(pH=2.5). The experimental conditions such as pH value, accumulation time, accumulation potential, and scan rate were investigated. Under the selected conditions, the peak current increased linearly with the concentration of FA in the range of 2.0x10"8 mol L'1 to l.OxlO"6 mol L"1. The detection limit was 5*10'9 raol L"1. The method was successfully applied to the determination of folic acid in drug sample, and the recovery was 93.9-96.9%. In addition, some electrochemical parameters about the electrode reaction were determined, such as electron transfer number (i.e. 2), standard potential E° (i.e. 0.79V vs. SCE), exchange current density j° (6.76x10"5 Acm'2), standard heterogeneous rate constant k° (3.50x10"2 cms"1) and the diffusion coefficient D (1.14xlO5 cmV). The influence of some surfactants was also studied.(3) The voltammetric behavior of rutin at a single-walled carbon nanotubes modified gold electrode was investigated by cyclic voltammetry and chronocoulometry. The modified electrode exhibited good promotion to the electrochemical reaction of rutin. At the modified electrode rutin can generate a pair of reversible redox peak in 0.1 mol L'1 phosphate buffer solution (pH 5.0). The anodic potential (Epa) and cathodic peak potential (Epc) is 0.375V and 0.328 V respectively. The experimental conditions such as pH value, scan rate, accumulation time and accumulation potential were investigated. When rutin is reduced on the surface of SWNT / Au, two electrons are transferred, accompanied by two protons. The electrode process is controlled by adsorption. Rutin can readily accumulate on the SWNT / Au electrode, and the surface coverage of rutin is estimated to be 2.12xlO"6mol.cm2. By chronocoulometry, the diffusion coefficient of rutin was determined to be about 1.94xlO"5 cmV. The addition of hemoglobin (Hb) can cause the peak current of rutin to decrease, which could be attributed to the formation of the supramolecular complex Hb-Rutin. The influence of some metal ions and organic molecules (including some surfactants) were also discussed. Under the selected conditions, the peak current increased linearly with the concentration of rutin in the range of 5.0*10"8 mol L'1 to 5.0xl0'6 mol L"1. The detection limit was 2.5xl0"8 mol L"1. The method was successfully applied to the determination of rutin in drug sample and flos sophorae.
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