Electrochemical Synthesis And Application In Detecting Amino Acid Of Polymer Modified Electrodes

Amino acid analysis is one of the most important technologys in industry, agriculture and life science. Aromatic amino acids include Phe, Tyr, and Trp, whose metabolize is significant in diagnosing diseases in liver, kidney and psychoneural. At present, there are many methods to clinically determine aromatic amino acids, such as HPLC, CE, fluorescence method, ultraviolet spectrophotometry, mass spectrometry. All of these methods need expensive apparatus, and three amino acids often interfere with each other.Electroanalytical chemistry is based on electrochemistry property and change of substance in solution, which has been applied widely in industry, agriculture, food inspection. Amino acid electrochemical analysis is simple, sensitive, polution-free, emission-free and able to be combined with modern separation methods, which largely simplify operation process, save analytical time and make it possess high accuracy and sensitivity. Amino acid electrochemical analysis includes direct and indirect analysis. Direct analysis requires substance is active on electrochemistry. In three aromatic amino acids, both Trp and Tyr are electrochemical active acids. They are essential amino acid, and Trp is limiting, so it is very meaningful to determine them.Chemically modified electrode is to fix molecular, ion and polymer of excellent chemical property on electrodes surface by chemical modification, which forms microstructure providing potential fields to make substances separated and enriched. And we can futher improve selectivity by controlling potential.Sensitivity of electrochemical analysis combined with chemical reaction selectivity of modifying agent has been an ideal method of separation, enrichment and selectivity, which is applied widely in selective enriching and separation, electro-catalysis, selective permeation, intermediary effect and chemical sensor.This thesis researched about the two aspects below:on one hand, fabricated the poly(p-aminobenzene sulfonic acid) modified glass carbon electrode (P-p-ABSA/GCE) by electrochemical polymerization, and study electrochemical behavior of Trp and Tyr on the P-p-ABSA/GCE systematically and minutely; on the other hand, investigate electrochemical polymerization of 2-mercapto aniline at gold electrod initiativly. The primary contents include:1. Poly(p-aminobenzene sulfonic acid) was modified on the surface of glass carbon electrode by Cyclic Voltammetry. With the increase of scan-round, the continuous rise of corresponding peak currents proves the formation of the polymer. This method is simple and fast, and the modifying film is stable and uniform and possesses good repeatability.2. The electrochemical behavior of L-Tryptophan (L-Trp) on the P-p-ABSA/GCE was studied and the influence factors such as supporting electrolyte, solution pH and scan rate were optimized. The results indicated that the oxidation peak current increased obviously on the modified electrode compared with that on the bare GCE. The number of proton participating in electrochemical reaction is same with electron and the electrochemical process is controlled by adsorption. In buffer solution (pH 3.0), the oxidation peak current increased linearly with the concentration of L-Trp in the range of 5.0×10-8～2.0×10-5 mol/L with the detection limit of 1.5×10-8 mol/L, and the relative standard deviation is 3.13% for 5.0×10-6 mol/L L-Trp (n=5). Some foreign species did not interfere with the determination of L-Trp.3. The electrochemical behavior of L-Tyrosine (L-Tyr) on the P-p-ABSA/GCE was studied and the voltammetric determination was optimized. The results indicated that the oxidation peak current increased obviously on the modified electrode compared with that on the bare GCE. The number of proton participating in electrochemical reaction is same with electron and the electrochemical process is controlled by adsorption. In 0.2 mol/L H3PO4 solution, the oxidation peak current increased linearly with the concentration of L-Tyr in the range of 2.0×10-7～2.0×10-5 mol/L with the detection limit of 1.0×10-7 mol/L, and the relative standard deviation is 4.95% for 5.0×10-6 mol/L L-Tyr (n=5).4. On regular electrodes Trp and Tyr can not separate, but on P-p-ABSA/GCE, in 2.0 mol/L H2SO4 solution by differential pulse voltammetry, oxidation peak potential of Trp and Tyr are 0.912 V and 1.016 V respectively so their oxidation peak separated perfectly. This method realizes selective determiniation to Trp and Tyr when they coexist. Use this method to detect Trp and Tyr in compound amino acid injection and the result is satisfactory.5. About electrochemical polymerization of 2-mercapto aniline at gold electrod, this thesis synthesized poly(2-mercapto aniline) (PATP) films on gold electrode by potentiostatic method. Having conductivity of polyaniline and oxidoreduction of -SH, the polymer have important prospect in research and exploitation of polymer electrode materials, and may be applied in battery positive materials. The electropolymerization process of 2-mercapto aniline on the gold working electrode and the oxido-reduction mechanism are studied. The results show that:2-mercapto aniline is electropolymerized through free cation radical and the major influential factors include the potential employed, the best of which should be between 1.38～1.43 V when using the method of potentiostatic. On this basis, the properties of the PATP was tested by cyclic voltammetry and the influences of polymerization potential, HCl concentration and polymerization time on the properties of PATP film were also discussed.