Amino Acid Research And Application Of Chemically Modified Electrodes

The research of chemically modified electrodes has been oneof the most flourish forward fields in the electrochemistry andelectroanalytic chemistry since it started in 1975.There are a lot of ways in the preparations ofchemically modified electrodes which have differentfunctions. In recent years, the research of the chemicallymodified electrodes is focused on the self-assembling films,inorganic substance films and the polymer films modifiedelectrodes. It is widely applied in many aspects such as lifescience, environmental science, analytic science, energysources science, material science and electronics. The polymerfilms have three dimension configuration , which suppliessome available energy field;the thickness of them is about10-1000nm , which has a lot of active group. The polymer filmshave electrochemical catalyze characteristics. On the otherhand ,the polymer films with selected chemical function grouphave some special character and expectable reactions takingplace on the films.Amino acid is the most essential matter in biological body,which has some special characters for having amino group andcarboxyl. Amino acid can be modified on the electrode bychemical way or electrochemical way. The modifiedelectrodes are applied for the determination of metal ion ,biological molecule, organic pollutant and so on ,which showssome special advantages.The main work and innovation of this paper are there: thefunction of MP-2 stripping analytical system was improved,amino acid such as cysteine and tryptophan has beenpolymerized on the electrode by the electrochemical way. Thepolymer film modified electrodes have been prepared. Theelectrocatalytic capability and absorbing capability havebeen investigated. It has not been found that the modifiedelectrode was studied with MP-2 stripping analytical systemfrom references. The modified electrodes have been appliedto the determination of dopamine, ascorbic acid andnorepinephrine. The way of determination is simple and thecost low;the pretreatment of samples to be determinated isunnecessary;the modified electrode responds quickly, andshows excellent selectivity, sensitivity, reproducibility andstability.I. DL-Valine is modified on the glass carbon electrode bythe electrochemistry method with LK-98 electrochemicalanalytical system and the electrochemical behavior of thedopamine on the modified electrode have been investigated. Theinvestigation shows that in pH4.0 phosphate buffer solutions,the linear range for the determination of dopamine was 5.0×10-7 mol/L～8.0×10-5 mol/L with the detection limit of 5.0×10-8 mol/L. The method is applied to the determination ofdopamine in the drug with satisfactory results.II. The ploy (L-cysteine)modified electrode is preparedwith MP-2 stripping analytical system. The high sensitivity andselectivity are accomplished in the determination and theaccumulative effect of the L-cysteine membrane. The method isvery easy and convenient,and it is possible to determinedopamine in the presence of high concentration of ascorbicacid.III. The best conditions of the preparation of L-cysteinemodified electrodes and the determination of ascorbic acid havebeen studied. It is investigated that ascorbic acid wasdetermined by linear sweep stripping voltammetry with themodified electrode. In pH 4.0 phosphate buffer solutions, theliner range for determination of ascorbic acid was 2.0×10-6~4.0×10-3 mol/L with the detection limit of 1.0×10-7mol/L.Therelative standard deviation for ten determinations of 1.0×10-4 mol/L ascorbic acid is 1.3%.The modified electrode showsexcellent stability and reproducibility.IV. The poly(tryptophan)modified electrode was preparedfirstly by the oxidative electropolymerization of CV and theeletrochemical behavior of norepinephrine on the modifiedelectrode was investigated. Results show that in 0.10mol/L PBS(pH6.0)the polymer exert an apparent catalytic effect on theNE oxidation and the interference of ascorbic acid onnorepinephrine determination is eliminated. The modifiedelectrodes shows good stability and reproducibility,and hasbeen applied to the analysis of the injection sample ofnorepinephrine successfully.