| The studies and applications of surfactants become more and more popular in electroanalysis since surfactant can change the structure of electrode/solution interface, and consequently improve the sensitivity and selectivity of electroanalytical methods. Additionally, the structure of surfactant film modified electrode is similar to the double-layer of biologic cell film, which is composed of lipoid. So the study of the electrochemical behavior of surfactant film modified electrode is of great benefit to get information of the electron transfer in the biologic body. In this thesis, the effects of different types of surfactants on the electrochemical response of some biological molecules and drugs were investigated. Moreover, different types of surfactant film modified electrodes were prepared, and characterized by scanning electron microscopy (SEM). Various electrochemical techniques were used to investigate the electrochemical responses of dioxygen on the modified electrode. The work is summarized as follows:(1) Polyvinylpyrrolidone (PVP) was used to modify carbon paste electrode. In the presence of cetyltrimethylammonium bromide (CTAB), the electrooxidation of thyroxine (T4) was studied by cyclic voltammetry on the modified electrode. T4 underwent totally irreversible oxidation at this system and a well-defined peak at 0.42 V was obtained. The influence of various surfactants on the oxidation of thyroxine was examined. The oxidation of T4 was facilitated by cationic surfactants CTAB. Chronocoulometry and AC impedance were also used to investigate the electrode process. T4 undergoes a four-proton and four-electron process, and the electron transfer rate of T4 was facilitated by CTAB. In the range of 2 x 10-7 - 9 x 10-6 mol/L, the oxidation peak current of T4 was linear with the T4 concentration and a low detection limit of 8 x 10-8 mol/L was obtained for 40s accumulation.(2) The acetylene black particle with high specific area was used to prepare the acetylene black electrode. In the presence of different surfactants,the electrooxidation of tetracycline (TC) was studied on the electrode. A sensitive oxidation peak appears at 0.58 V in the presence of the anionic surfactant sodium doddecyl sulfate (SDS), indicating that the oxidation of TC was facilitated by SDS. AC impedance, chronocoulometry and cyclic voltammetry were used to investigate the electrode process, indicating the diffuse coefficient of and electron transfer rate of TC was facilitated by SDS. The phenolic substituent in position ten of TC is responsible for the oxidation peak. The phenolic substituent may have lost four protons and four electrons and can be oxidized to benzoquinone. The benzoquinone was also reduced, forming a reversible redox couple hydroquinone / benzoquinone, which was adsorbed at the acetylene black electrode surface. In the range of 1.2 10-7 -1.5 10-5 mol/L, the oxidation peak current was linear with the TC concentration and a low detection limit of 6.0 10-8 mol/L was obtained for 150s accumulation. The good reproducibility and sensitivity were obtained. Under optimized experiment conditions, the method has been used to determine TC in honey and pharmaceutical, and the results compared favorably.(3) In the presence of different surfactants, the electrochemical response of noradrenalin (NA) was studied on the acetylene black electrode. The results of cyclic voltammetry and AC impedance indicated that the electrochemical response of NA in acid media was facilitated by the anionic surfactant SDS. The redox peak of NA is corresponding to the redox of the oxophenic acid part in the structure of NA, i.e. the reversible redox couple oxophenic acid / o-quinone. In the range of 6 10-8- 7.2 10-6 mol/L, the oxidation peak current of NA was linear with the NA concentration and a low detection limit of 6.0 x 10-9 mol/L was obtained for 70s accumulation. Under optimized experiment conditions, the method could be used to determine NA in biological sample.(4) Different type...
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