Preparation Of Silver Doped Poly (l-aspartic Acid) Modified Electrode And Its Application

Abatract: In this paper, the preparation of silver doped poly(L-aspartic acid) modified electrode was studied. By cyclic voltammetric, the electrochemical behaviors and electrode reaction mechanisms of dopamine(DA), epinephrine(EP), catechol(CC) et al also were studied at the modified electrode. The form of DA and EP in electrochemical process and the characters were discussed, furthermore, the electrochemical properties of catechol(CC) ,hydroquinone(HQ) and resorcinol(RS) were investigated at the modified electrode. Because of the similar electrochemical properties of them, the redox peaks overlap at most solid electrodes or chemical modified electrode. It was too difficult to simultaneously determine catechol(CC), hydroquinone(HQ) and resorcinol(RS). Because of the synergistic effect of amino acid and silver nanoparticles, the special properties of Both silver nanoparticles modified electrode and amino acid modified electrode were combined at the silver doped poly(L-aspartic acid) modified electrode. The novel method was successfully applied for individual or simultaneous determination of CC, HQ and RS. A simple, cheap and efficient method was acquired for the determination of CC, HQ and RS in water sample with satisfactory results. A good theoretical and experimental basis was provided for on-line analysis, such as industrial wastewater and domestic wastewater.In this research , the main problems must be solved were: 1) To investigate the preparations and properties of the silver doped poly(L-aspartic acid) modified electrode; 2) To research the electrochemical properties of DA and calculate its kinetic parameters; 3) To research the electrochemical properties of EP and calculate its kinetic parameters; 4) To discuss the individual determination for the electrochemical properties of CC, HQ and RS; 5) To discuss the simultaneous determination for the electrochemical properties of CC, HQ and RS.The major works are researched as follows:1. The silver doped poly(L-aspartic acid) modified electrode was prepared by cyclic voltammetric method. The immobilization conditions of silver and L-aspartic acid on a glassy carbon electrode were studied. The modified electrode has better respond to dopamine, adrenaline et al.2. The electrochemical behavior of dopamine has been studied at Ag-PLA/GCE and the novel determination mothod of dopamine were established. In pH7.0 phosphate buffer solution, the peak potentials were 0.191V of Epa and 0.161V of Epc (νs Ag/AgCl) at the scan rate 50mV/s. The linear range for the determination of dopamine were 2.00×10^-71.00×10^-5mol/L and 1.00×10^-55.00×10^-4 mol/L. The detection limit was 5.0×10^-8mol/L. The method was applied for the determination of dopamine in drug and urine with satisfactory results.3. The electrochemical behavior of epinephrine has been studied at Ag-PLA/GCE and the novel determination mothod of epinephrine were established. In pH=3.5 phosphate buffer solution, the modified electrode gave a pair of redox peak potentials at 0.447V and 0.387 V for EP at the scan rate 50mV/s. The linear ranges for the determination of epinephrine were 8.0×10^-81.0×10^-5 mol/L and 1.0×10^-51.0×10^-4 mol/L. The detection limit was 8.0×10^-9mol/L. The relative standard deviations was 3.2% for the determinations of EP for 40 continuous measurements. The signal was highly stable and reproducible. This method was applied to the determination of epinephrine in drug and urine with satisfactory results.4. The electrochemical behavior of catechol has been studied at Ag-PLA/GCE. In pH=7.5 phosphate buffer solution, the redox peak potentials of catechol were 0.154V of Epa and 0.123V of Epc (νs Ag/AgCl) at the scan rate 20mV/s. The anodic peak current increased linearly with the catechol concentration over the range from 5.00×10^-8 mol/L to 1.00×10^-4 mol/L by cyclic voltammetry at the scan rate of 160mV/s.The detection limit was 3.0×10^-8mol/L. This method was applied to the determination of catechol in water sample with satisfactory results.The electrochemical behavior of hydroquinone has been studied at Ag-PLA/GCE. In pH=7.5 PBS,the modified electrode gave the redox peaks potentials of hydroquinone at 67mV and 35mV, and the scan rate is 20 mV/s. A linear response of the anodic peak current with the concentration of hydroquinone was obtained in the range of 1.00×10^-6mol/L¹.00×10^-4mol/L and 1.00×10^-4 mol/L⁵.00×10^-4mol/L. The detection limit was 3.0×10^-7mol/L. This method was applied to the determination of hydroquinone in water sample with satisfactory results. The electrochemical behavior of resorcinol was studied at Ag-PLA/GCE and the novel determination mothod of resorcinol were established. In pH=2.5 PBS, the modified electrode gave a sensitive anodic peak potentials at 910mV, and the scan rate is 50 mV/s. A linear response of the anodic peak current with the concentration of resorcinol was obtained in the range of 3.00×10^-6mol/L¹.00×10^-4mol/L and 1.00×10^-4 mol/L¹.00×10-3mol/L. The detection limit was 1.0×10^-6mol/L. This method was applied to the determination of resorcinol in water sample with satisfactory results.5. The electrochemical behavior of catechol,hydroquinone and resorcinol have been studied at Ag-PLA/GCE. In pH=2.5 phosphate buffer solution(PBS), three anodic peaks appeared at 0.466V, 0.361V and 0.831V corresponding to CC, HQ and RS were given at the modified electrode by linear sweep voltammetric method. Separation of the anodic peak potentials between CC, HQ and RS were about 0.105V(CC and HQ), 0.470V(HQ and RS) and 0.575V(CC and RS), respectively. So it was possible to detect the mixture of CC, HQ and RS. Under the optimum conditions, the linear ranges were 5.00×10^-7 mol/L³.00×10^-5 mol/L and 3.00×10^-5 mol/L³.00×10^-4 mol/L for CC, 5.00×10^-7 mol/L¹.00×10^-4 mol/L and 1.00×10^-4 mol/L⁸.00×10^-4mol/L for HQ, 5.00×10^-6 mol/L¹.00×10-3mol/L for RS .The detection limits are 1.0×10^-7 mol/L, 3.0×10^-7 mol/L and 5.0×10^-7 mol/L, respectively. The method was applied to simultaneous determination of CC, HQ and RS in water sample with satisfactory results.Based on above results , it was indicated that the silver doped poly(L-aspartic acid) modified electrode show good electrochemical activity to the determination of DA, EP, CC, HQ and RS. Under the optimum conditions , the simultaneous electrochemical determination of CC, HQ and RS was achieved through the anodic peak separation of them. The method was successfully used for the simultaneous electrochemical determination of CC, HQ and RS in water sample with satisfactory results.