Study On Capillary Electrophoresis With Amperometric Detection And Its Applications

Capillary Electrophoresis (CE) is one of the most important separation techniques in recent twenty years. Because the theoretical plate number is great developed to tens of thousands and even millions and the volume of sample injection reaches nano milliliter level in CE analysis, it is studied and applied to most analytical areas. However, the small sample injection volume and very thin capillary bring about difficulties to detections. The common used detection methods are ultra-violet (UV), laser induced fluorescence (LIF), mass spectra (MS) and electrochemical detection (ED). Every detection method performs some advantages and suffers from some shortages too. For example, LIF and MS are very sensitive but the instrumentations are very expensive, and some complicated derivation procedures are needed. Amperometric detection (AD), one kind of electrochemical detections, is more sensitive than the common used UV detection, and have many merits when coupled with CE, such as simple instrumentation and operation, low cost, wide linear range, etc. The combination of CE with AD is extensively studied and applied in most analytical fields for its above advantages.The advantages of CE in separation efficiency and instrumentation are obvious when compared to HPLC. However, the concentration detection sensitivity of CE is much lower than HPLC owing to its smaller sampling volume and the short light distance when coupled with UV or FI detectors. The detection sensitivity of CE could be great improved by some special characters itself such as field-amplification-injection and isotachophoresis.One goal of this dissertation is to explore the methods of improving the sensitivity of CE-AD. Another one is applying this CE-AD technique to resolve some actual analytical problems in pharmaceutical analysis, biochemical analysis and food analysis. The contents of this dissertation include six chapters:In the first chapter, the characteristics of CE, the separation models and basictheories of CE, the detectors, the sensitivity-enhanced methods, the studies and applications of CE-AD simply is introduced. The goal and significance of this dissertation are introduced too.Chapter 2 includes two sections. In the first section, capillary zone electrophoresis (CZE) with amperometric detection (AD) was firstly applied to the simultaneous determination of rutin (RT) and hydrochlorothiazide (HCT) in compound Chinese herb medicines and human urine samples. The two analytes could be perfectly analyzed within 12 min and showed significant current responses at carbon electrode under the optimum conditions and their detection limits were 5.0x10-7 molL-1 and 2.0x10-7 molL-1 respectively (S/N=3).In the second section of this chapter, we explored the effects of diluents during electro-kinetic sampling on field amplification injection by studying the changes of current responses of clonidine hydrochloride, hydrochlorothiazide and rutin which are originally positive, neutral, negative respectively in water solution when diluted in different solvents. It was found that the simultaneous field amplification injection for positive and negative particles could be carried out by changing the acidity of samples. This method is much easier than converting electricity polarity. The effect for negative particles could be also reached by using buffer solution with higher concentration as diluents. The detection sensitivity of different ingredients existed in one sample could be adjusted and then their current responses could be reach the same magnitude level by using suitable diluents. For example, the current responses of clonidine hydrochloride, hydrochlorothiazide and rutin are difficult to compare clearly in the same electropherogram if using the running buffer as diluent because their contents are different in one hundred times. But, their current responses could be compared clearly in one electropherogram if water is used as the diluent.Chapter 3 includes two sections too. In the first section, the indirect determination of hydroxyl radical (OH) b...