【作者】 赵学财；

【导师】 申大忠；

【作者基本信息】 山东师范大学 ， 分析化学， 2011， 硕士

【摘要】 电导检测是一种简单通用型的检测技术,作为一种色谱检测器主要应用于无机离子及某些其它检测手段难以检测的有机离子的分析。电导检测中的电极有两种放置方式,一种是把两电极放置于溶液当中（接触式电导检测）,另一种是电极与溶液被绝缘材料隔离（非接触式电导检测）。接触式电导检测器在毛细管电泳的应用中遇到了困难,如在毛细管壁上打孔置入电极需要较高的制备工艺,检测电极容易被污染,电极的清洗和更换不便,分离电压干扰严重等。电容耦合非接触式电导检测（C₄D）是近几年发展起来的一种用于毛细管电泳和微流控芯片的新型检测技术。这种检测池具有池体积小,结构简单、制备方便,彻底解决了接触电导检测存在的检测电极易污染、受被测系统高场强电压干扰等问题,是一种应用前景良好的检测器。与C₄D的应用范围正在不断扩大相比,有关C₄D的理论研究报道较少,虽然文献中也提出了一些等效电路模型分析其响应特性,但大多停留在对实验规律的简单定性描述,未涉及各参数的取值及其计算方法,因此相关的理论研究目前依然是薄弱环节。在毛细管电泳的实验条件下,源自非接触电极与管壁之间的电阻抗很高,并成为制约C₄D的检测灵敏度的关键因素之一。针对这两个问题,本论文讨论在不同条件下各参数的取值规律,进而模拟分析C₄D的响应特性,并在此基础上开展了一种低阻抗型电容耦合非接触电导检测器（LIC₄D）的响应理论与应用研究。主要工作如下:一、非接触式电导检测器的等效电路模拟与分析基于C₄D的等效电路模型,设计了接触式并排电极、平面双并排电极、接触式圆管电极、非接触式并排电极、非接触式圆管电极等简化的电极系统,模拟C₄D的阻抗行为,通过阻抗测定与分析,讨论在不同条件下各等效电路参数的取值规律,为模拟分析C₄D的响应特性、优化该检测器的参数提供有价值的技术参数。二、低阻抗型非接触式电导检测器响应研究与应用为降低C₄D检测池体积,设计了对电极式的C₄D,但该装置阻抗虚部的绝对值是远远大于实部的绝对值,限制了检测溶液电导率变化的灵敏度。为提高对电极式C₄D的响应灵敏度,采用阻抗湮灭原理,将压电石英晶体与C₄D串联组合,在其谐振频率下,检测回路中阻抗的虚部为零,有效地降低了其管壁电容的高阻抗对C₄D检测灵敏度的制约,通过理论模拟与实际验证,其检测灵敏度接近于接触式电导检测。三、基于纵波响应的液体密度压电传感器石英晶体微天平是一种高灵敏的质量传感器,在界面传质过程监测中有广泛的应用,当压电传感器在液相谐振时,除产生厚度剪切波外,通常伴随纵波,纵波可能对厚度剪切波产生干扰,在极端情况下还会造成压电传感器在液相中的谐振峰分裂。本章系统研究了这种谐振峰分裂现象,对其产生的机理进行了理论分析,并讨论了溶液密度的影响,在此基础上研制了基于纵波效应的液体密度压电传感器,通过纵波反射器与消除器的切换,结合阻抗分析法,可用压电传感器同时测定电极表面质量、液体的密度、粘度的变化。更多还原

【Abstract】 Conductivity detection is a simple and universal detection technique for inorganic and in some cases even organic ions in ionic chromatographic and electrophoretic systems, which are often not readily detected by other techniques. For conductivity detection, the metal electrodes can be in direct contact with liquid (galvanic detection) or separated from liquid with an insulating film (contactless detection). The contact conductivity detector has encountered the difficulty in the application of capillary electrophoresis. To design of the micro-conductivity cell in capillary, drills on the capillarity wall and implant electrodes need a high technical process. In addition, the detection electrodes are easily contaminated and inconverental for cleaning and replacement. The separation voltage affects the performance of the detector.Capacitively coupled contactless conductivity detection (C4D) is a new detection technique, which has been developed in recent years and used mainly in capillary and microchip electrophoresis. The C4D offers the advantage in simplicity in detection cell design, smaller volume, and it completely overcame the disadvantages of electrodes fouling and interference of separation voltage on measurement signal. Compared with the application range of the C4D, the related C4D fundamental research report is few. Although some of the equivalent circuit model is proposed to analyze the response characteristics, they mainly make some qualitative description to experiment rules. The computational method is still a weak link in the fundamental research at present. Under the capillary electrophoresis conditions, the high impedance between the contact electrodes and the liquid is one of the factors for the low sensitivity of C4D detector. This thesis discusses the various parameters under different conditions, and simulates the response characteristics of C4D, and on this basis, a low impedance capacitively coupled contactless conductivity detector (LIC4D) is proposed. The main contents of this thesis are listed below:1、Equivalent circuit simulation and analysis for contactless conductivity detectorBased on the equivalent circuit model of the C4D, simulated detectors including contact parallel plate electrodes, contact double parallel plate electrodes, contact parallel column electrodes, contactless parallel plate electrodes, and contact parallel column electrodes were designed to analyze the electric behavior of the C4D. The impedance data were measured and analyzed. The changes in the equilivalent circuit parameters were discussed. This analysis is helpful to simulate the response of the C4D and the optimization in detector parameters.2、Fundamental research and application of low impedance contactless conductometric detectorTo reduce the C4D detection cell volume, a C4D with two opposite contactless electrode was designed. Howerver, the sensitivity of this detector to the changes of solution conductivity is poor due to the fact that the absolute value of imaginary part. In order to improve the response of the sensitivity of this C4D, we adopt the principle of impedance annihilation. A quartz crystal resonator was added in series combination of the C4D. Under the resonance frequency of the combination, the imaginary of the impedance is close to zero. The influence of the wall capacitor impedance on the sensitivity of the C4D is reduced effectively. It was shown that sensitivity of the low impedance C4D is closes to that of a contact conductivity detector.3、Piezoelectric quartz crystal liquid density sensor based on longitudinal wave responseQuartz crystal microbalance is a sensor with high sensitivity to the change in surface mass change. It has found wide applications in monitoring the mass changes in insurface processes. When a piezoelectric quartz resonantor is operated in liquid phase in thickness shear model, a longitudinal wave is usually occurred. The longitudinal wave is a potential error source for the measurement of thickness shear model. Under some extreme cases, the renant peak of the resonator is split to a group of small peaks. In this chapter we studied the resonance peak cleavage by an impedance analysis method. The interaction between the thickness shear wave and longitudinal wave was investigated. The influence of liquid density was discuused. By the comdination of a longtudianl wave reflector and longtudianl wave eliminator, the changes in surface mass, liuid density, and liquid viscosity were imultaneously determined by a piezoelectric sensor in impedance analysis method.更多还原