Study On Capillary Electrophoresis With Electrochemical Detection And Its Applications

Capillary Electrophoresis(CE) is becoming increasingly recognized as one of the most important separation techniques in recent twenty years due to its speed, efficiency,reproducibility,ultra-small sample volume,and ease of Clearing up the contaminants.Because the theoretical plate number is greatly developed to tens of thousands and even millions,and the volume of sample injection reaches nano milliliter lever in CE analysis,it has been studied and applied to most analytical areas. Electrochemical detection is usually more sensitive than UV detection for electroactive species,and has many advantages when it combines with CE,CE-ED offers high sensitivity and good selectivity for electroactive species.The goal of this thesis is to explore some applications in Chinese traditional medicine analysis,human body fluid analysis,control of cosmetic safety and determination of physicochemical constant by CE-ED.The major content is as follows:1.PrefaceThe development of CE,the basic theories of CE,the CE detectors,the studies and applications of CE-ED are introduced simply.The goal and significance of this thesis are introduced too.2.Determination of Active Components in Bamboo Leaves and Bamboo-leaf Tea by Capillary Electrophoresis with Electrochemical DetectionA simultaneous determination of vanillin,trans-ferulic acid, p-hydroxybenzaldehyde,p-coumaric acid,vanillic acid,4-hydroxybenzoic acid and caffeic acid in five different kinds of bamboo leaves and bamboo-leaf tea by capillary zone electrophoresis with electrochemical detection(CE-ED) was reported.The effects of several important factors were investigated to acquire the optimum analysis conditions.A 300μm diameter carbon disc electrode was used as the working electrode positioned carefully opposite the outlet of capillary at potential of +0.95 V (vs.SCE).The analytes could be well separated within 22 min at a separation voltage of 16 kV in a 60 mmol/L borate buffer(pH＝8.7).There is excellent linearity between peak.current and concentration of seven analytes over two or three orders of magnitude with the detection limits(S/N＝3) ranging from 1.9×10^-8 g/mL to 9.8x10^-8 g/mL.The proposed method has been successfully applied to the analysis of real samples with satisfactory results.3.CE determination of creatinine and uric acid in saliva and uric acid during excise.A simple and reliable method based on capillary electrophoresis with electrochemical detection(CE-ED) was applied to study the effect of aerobic exercises on creatinine and uric acid concentration in saliva and urine.The pH value, the running buffer concentration,the SDS concentration,separation voltage,injection time and the potential applied to the working electrode were investigated to find the optimum conditions.The detection limits(S/N＝3) for creatinine and uric acid were 3.6μmol/L and 0.86μmol/L,respectively.This method was successfully first used in the rapid analysis of creatinine and uric acid in saliva samples.After aerobic exercises, creatinine concentration decreased,and uric acid concentration increased in saliva.In urine,the concentration of creatinine and uric acid both increased after exercise.4.Determination of diethylene glycol in toothpaste by capillary electrophoresis with electrochemical detection.A capillary electrophoresis technique with electrochemical detection(CE-ED) for the determination of diethylene glycol(DEG) in toothpaste was described.Effects of several factors,such as the pH value and the concentration of the running buffer, the separation voltage,the injection time and the potential applied to the working electrode,were investigated to find the optimum conditions.With a length of 75 cm, 25μm inner diameter fused-silica capillary,well-defined separation of diethylene glycol from propylene glycol and glycerol was achieved in the running buffer.While operated in a wall-jet configuration,a 300μm copper disc electrode used as the working electrode,the applied potential was +0.65 V(vs.SCE),the separation voltage was 16 kV,the above three analytes could be well separated in an 80 mmol/1 borate buffer(pH＝9.2).The linear range of DEG was from 8.4×10^-4 g/mL to 4.2×10^-6 g/mL. Notably,the DEG detection limit(S/N＝3) of 1.5×10^-6 g/mL could meet the safety criterion of this compound.This method was successfully used in the rapid analysis of DEG in several toothpaste samples.The average recoveries of 96.9%-102.9% indicated that the experimental results were satisfactory.5.Determination of pKa value of salicyl alcohol by capillary electrophoresis with electrochemical detectionA simple and rapid method based on capillary electrophoresis with amperometric detection(CE-AD) to calculate the dissociation constant of salicyl alcohol and phenol is described.The effects of several factors,such as the potential applied to the working electrode,injection time,and separation voltage,were investigate to find the optimum conditions for pKa determination.Operating in a wall-jet configuration,a 300μm carbon disk electrode used as the working electrode exhibited good response at 0.86 V(vs.SCE) for salicyl alcohol and phenol.The effective mobilities of salicyl alcohol at different temperatures were determined by monitoring the migration time changes of salicyl alcohol and phenol.The dissociation constants of salicyl alcohol and phenol were calculated to be 9.94 and 9.96,respectively,which are in good agreement with the literature.