Study Of Chemically Modified Electrode On The Application Of Capillary Electrophoresis With Amperometric Detection

Capillary electrophoresis(CE)is a powerful liquid phase separation technique. The separation principle is based on the phenomena that ionized molecules of different mass and charge will travel with different velocities through a fused silica capillary under the influence of a high-voltage electric field.Owing to the high separation efficiency,rapid analysis,minimum consume of samples and environmental friendliness,it has flourished in wide areas such as environmental analysis,pharmaceutical analysis,biochemical analysis,and food analysis etc.There are many detection methodologies coupled with CE,such as UV-Visible detection(UV-Vis),Laser Induced Fluorescence detection(LIF),Electrochemical detection(ED)and Mass Spectrum(MS).The major barriers for CE system integration with LIF and MS etc.are fluidic interface,sample pretreatment (fluorescence derivatization or labeling),etc.Since ED,especially amperometric detection(AD)has much advantage over other widely used techniques in that it is much more economical,without complicated pretreatment procedure,and it provides good selectivity as well as high sensitivity,it has flourished to various areas.From the standpoint of broadening its application areas,we mainly focus on the development of new chemically modified electrode(CME)and new method of CE-AD.This paper begins with a brief introduction of CE,its separation models as well as various detection methodologies.Chapter 2 is the determination of three kinds of carbohydrate together with ascorbic acid by capillary zone electrophoresis with amperometric detection (CZE-AD)at a carbon paste modified electrode.In this paper,a kind of novel carbon paste electrode modified with double modifiers- polyethylene glycol(PEG)and Cu₂O(PEG-Cu₂O CPME)in CZE-AD was applied to simultaneously determine glucose,sucrose,fructose and ascorbic acid(AA).The catalytic electrochemical properties of PEG-Cu₂O CPME could enhance sensitivity obviously compared with carbon paste electrode modified with only PEG or Cu₂O at a relatively lower detection potential(+0.3V vs.SCE).The four analytes could be perfectly separated within 22 min,the linear ranges were from 1.0×10^-6to 5.0×10^-5mol L^-1and the detection limits were at 10^-7mol L^-1magnitude(S/N=3).The present working electrode was successfully employed to analyze beverage samples with recoveries in the range 93～107%and RSDs less than 4%.The results demonstrated that CZE coupled with the PEG-Cu₂O carbon paste modified electrode was of convenient preparation,high sensitivity,good repeatability and could be used in the rapid determination of practical samples.Chapter 3 states the development of a novel double modifier carbon paste electrode - a MWCNT-Cu₂O CPME and its application on several amino acids. Amino acids are essential building blocks of biological molecules.Though they are so important to human beings,it is to some extent very difficult to separate and determine amino acids because of their adsorbability to silica capillary and non-optical and non-electrochemical activity for detection.In this paper,a carbon paste electrode modified with multiwall carbon nanotubes and copper(â… )oxide (MWCNT-Cu₂O CPME)was fabricated and the electrochemical behaviors of nineteen kinds of natural amino acids at this modified electrode were studied.The MWCNT-Cu₂O CPME was also successfully applied to the CZE-AD of six kinds of amino acids.Under the optimal conditions,these amino acids could be perfectly separated within 20 min and their detection limits were as low as 10^-7or 10^-8mol L⁹-1) magnitude(S/N=3),which demonstrated that MWCNT-Cu₂O CPME could be successfully employed as an electrochemical sensor for amino acids with some advantages of convenient preparation,high sensitivity and good repeatability.The last chapter is focus on the optimization of CZE for a complicated system. Chrysanthemum is a herbaceous perennial plant possessing antimicrobial, antibacterial,antifungal,antiviral and anti-inflammatory activities,which mostly owing to it ingredients of flavonoids.Here in this research we focus on the CZE separation of six kinds of flavonoids in chrysanthemum.With the help of different additives into buffer and sample,they could get baseline separation within 20 min and the LOD could reach 10a^-8g mL^-1magnitude.The successful practical application on the determination of chrysanthemum samples confirmed the validity and practicability of this method.