| 其他摘要 | 电位型传感器是化学传感器中的一个重要分支，已成功应用于工业分析、环境监测和生物医学等领域。近年来，随着各种新型能量转换模式和传感材料的发现、新的检测原理的引入以及非传统电位响应模型的建立，电位检测技术的研究领域不断拓展。然而，相对滞后的样品前处理技术以及粗糙的离线手工操作影响了电位分析结果的准确度和重现性，限制了该技术的实际运用。流动分析是一种高效率的溶液处理技术，可将各种复杂单元操作融为一体，具有广泛的适用性。本论文将电位型传感器与流动分析技术联用，结合停流、在线分离与富集、固相萃取、分子印迹等技术，提高了电化学检测性能，实现了分析的自动化。该联用技术综合利用了电位传感器的高灵敏度、高选择性以及多种现代前处理技术对复杂基质中样品的高效分离、富集能力，开辟了实际样品分离和检测的新思路。本论文涉及电位型传感器与电化学富集、分子印迹固相萃取、流动注射和高效液相色谱四方面的联用技术研究，具体内容如下：1、电化学在线富集-离子选择性电极电位检测联用技术研究离子选择性电极是电位传感器主要研究领域，其理论检测限可达纳摩尔水平。但是基体效应的干扰使离子选择性电极难以达到理想的检测限。对于海水样品，高浓度的干扰离子限制了电位检测技术的直接应用。为解决上述问题，本研究将在线样品预处理技术及电化学富集技术与低检测限离子选择性电极电位分析法相结合，提高了系统的响应性能及分析效率，开发出了能够快速检测海水中重金属浓度的新型传感器技术。通过在线过滤（去除海水中颗粒杂质）、紫外线消解（释放被有机物络合的金属离子）、电化学富集（消除海水基体效应及其它离子的干扰、富集待测金属离子）以及离子选择性电极电位测定等过程，实现对海水重金属的高灵敏、高选择性的快速检测。在海水基体条件下，对于镉、铅和铜离子测定的线性范围分别为1.0×10-9～1.0×10-7 mol/L、3.0×10-9～1.0×10-7 mol/L和1.0×10-9～1.0×10-7 mol/L，相应检测限为2.8×10-10、6.6×10-10和5.1×10-10 mol/L（3σ），连续六次测量的RSD均小于5 %，整个分析过程在25 min内完成。应用于实际海水样品分析，其测定结果与溶出伏安法一致。该联用技术性能可靠、成本低廉，在海水重金属现场快速监测方面具有良好的应用前景。2、分子印迹固相萃取-电位检测联用技术研究固相萃取是一种应用广泛的样品前处理技术。其常用的吸附剂有C18、C8、硅藻土、硅胶以及氧化铝等，然而上述吸附剂依据被分析物的极性进行分离，对于极性相近的化合物缺乏选择性，难以用于复杂基体如海水中有机污染物的分离。分子印迹聚合物由于具有构效预定性、特异识别性和广泛实用性等特点，可望解决上述问题。本研究采用以分子印迹聚合物为高选择性吸附剂的固相萃取技术实现对海水中痕量有机污染物的高效分离富集，以碳纳米管修饰电极为传感器敏感元件实现对电中性有机分子的高灵敏电位检测。通过选择合适的功能单体及交联剂，优化聚合反应实验条件，提高了分子印迹聚合物对有机分子识别的特异性，取得最佳的分离富集效果，消除了海水基体效应及复杂组分的干扰；制备了碳纳米管修饰电极，利用单壁碳纳米管与电中性有机分子之间的π-π和疏水作用，对其进行直接电位测定；结合在线过滤、固相萃取分离富集等流动分析样品自动化预处理技术，提高了传感器体系的响应性能及分析效率。以环境中常见的多环芳烃荧蒽为研究对象，开发出一种能够快速检测海水中荧蒽浓度的新型电化学传感器系统，其线性范围为25～150 ppb，检测限可达6.3 ppb，加标回收率在95～105 %之间。该方法提供了一种检测有机污染物的新方法，拓宽了电位技术的应用范围。3、新型流动注射电位检测器的研制流动注射技术必须与其它检测手段结合才能形成完整的分析方法，常用的检测方法包括紫外、荧光、电流和电导法。电位检测器具有选择性好、灵敏度高、造价低等特点，在流动注射分析中发挥着不可替代的作用。常规的电位检测利用电极对物质的直接响应，向系统引入能够与待测物质发生化学反应的指示离子，监测指示离子浓度变化的间接方法可以实现更多物质的测定。但是额外试剂的加入能够引起峰展宽。本研究开发出一种新型电位检测器，利用聚合物膜离子选择性电极的离子通量，原位产生指示离子，有效避免了峰展宽。在该体系中，聚合物敏感膜不仅作为试剂可控释放的载体，而且作为换能元件，实现待测物质的高灵敏检测。以高锰酸根离子选择性电极作为试剂原位释放和换能方式，实现了紫外吸收较弱的抗坏血酸、多巴胺和去甲肾上腺素的测定，三者的线性范围分别为1.0×10-5～2.5×10-7 mol/L、1.0×10-5～5.0×10-7 mol/L和1.0×10-5～5.0×10-7 mol/L，相应检测限分别为7.8×10-8、1.0×10-7和1.0×10-7 mol/L。为验证此方法的通用性，采用铜离子选择性电极实现了组氨酸、精氨酸、苏氨酸、甲硫氨酸、缬氨酸、半胱氨酸和苯丙氨酸7种无电活性物质的检测，在一定范围内，峰高与氨基酸浓度呈线性关系。将该方法用于实际样品的测定，结果准确。4、高效液相色谱分离-电位检测联用技术研究高效液相色谱是分离科学的重要研究领域，本研究将流动注射电位检测器扩展到高效液相色谱中。值得注意的是，在快速分离体系中，检测器必须可逆性好，否则会造成严重的峰拖尾、分离度差等问题。本研究采用外电流驱动试剂的可控释放，极大地提高了检测器的可逆性。采用反相色谱同时测定了苏氨酸、亮氨酸、甲硫氨酸、组氨酸和苯丙氨酸，5种氨基酸均达到基线分离。检测限（3σ）为：苏氨酸，2.6×10-6 mol/L；亮氨酸，1.0×10-6 mol/L；甲硫氨酸，7.3×10-7 mol/L；组氨酸，6.8×10-8 mol/L；苯丙氨酸，1.8×10-6 mol/L。该电位检测器作为高效液相色谱及流动注射分析的检测手段，使研究对象得到了扩展，可以实现对无紫外吸收、无荧光信号或非电活性物质的测定。; Potentiometric sensors, an important subclass of chemical sensors, have received considerable attention in the fields of industrial, environmental, and clinical analyses. In recent years, many efforts are made in the introduction of new transduction principles and new sensing materials, allowing the development of numerous new sensors. In many cases of practical relevance, however, rough sample pretreatment and off-line manual operation may lead to inaccuracy and poor reproducibility of analytical results. Flow analysis is recognized as a very attractive way for the implementation of automated analytical procedures, exhibiting evident advantages that are mainly related to the multiple tasks assigned to single analytical determination. In case of flow measurements additionally one can favorably employ on-line separation of the analyte from the matrix. This dissertation describes hyphenated systems for the potentiometric sensors with flow analysis to improve the performance of the sensors and to realize automatic detection. These works include combination potentiometric sensors with electrochemical preconcentration, molecular imprinted polymers solid extraction, flow-injection analysis (FIA) and high-performance liquid chromatography (HPLC). The detail contents are as follows:1. Study on the combination of electrochemical preconcentration with potentiometric detection using an ion-selective electrode (ISE)ISEs, the best known types of potentiometric sonsors, are today sufficient well understood and optimized to reach subnanomolar level detection limits for numerous ions. However, a high electrolyte background hampers the attainable detection limits. A particularly difficult sample matrix for potentiometric detection is seawater, where the high saline concentration forms a major interfering background. In the present work, we have developed a hyphenated system for the online electrochemically modulated preconcentration and matrix elimination of trace metals, combined with a downstream potentiometric detection with solid-contact polymeric membrane ISEs. Processes including on-line filtration (to remove impurity particles in seawater), UV digestion (to dissociate heavy metals complexed with organic compound), electrochemical enrichment (to circumvent matrix interferences arising form the saline sample medium and to preconcentrate target ion), and potentiometric detection have been involved in the system for sensitive, selective and rapid detection of heavy metals in sea water. This concept has been successfully evaluated with cadmium, lead and copper as model trace elements. The linear response ranges were 1.0×10-9 - 1.0×10-7 mol/L for cadmium, 3.0×10-9 - 1.0×10-7 mol/L for lead and 1.0×10-9 - 1.0×10-7 mol/L for copper, respectively with the corresponding detection limits (3σ) of 2.8×10-10, 6.6×10-10 and of 5.1×10-10 mol/L. For six successive measurements, the results showed relative standard deviations (RSD) of less than 5 %. The whole analysis process was completed within 25 min. The system has been applied to determination of heavy metals in seawater and the results agreed with those obtained by stripping voltammetry. With advantages of simplicity, accuracy and low cost, the sensing system offers promising potentials for on-site analysis of heavy metals in seawater.2. Study on the combination of molecular imprinted polymer solid extraction with potentiometric detectionSolid-phase extraction (SPE) is a commonly utilized method for sample pretreatment, with C18, C8 diatomaceous earth, silica and alumina as sorbents. However, these sorbents suffer from low selectivity toward target compounds, thus elution with solvents of varying polarity is required to separate compounds according to polarity difference, and more solvents, manpower, and time are required. The technique of molecular imprinted polymers (MIPs) has been shown to be capable of producing materials with ‘‘antibody-like’’ selectivities. Herein, MIPs were prepared and applied as SPE sorbent for selective preconcentration and specific recognition of trace organic pollutants in seawater. Some variable parameters influencing the final characteristics of the obtained materials in terms of capacity, affinity and selectivity for target analyte such as the nature of functional monomers, cross-linkers were investigated in detail. Under optimal conditions, the MIPs as sorbent could be successfully applied to preconcentration and separation of organic pollutants. Matrix interferences arising from the complex sample medium are thus circumvented. Then a single-walled carbon nanotubes (SWCNTs) modified electrode was developed to detect neutral organic molecules, mainly through π-π and hydrophobic interactions. The new concept has been evaluated and illustrated for the detection of trace fluoranthene as an example of high practical importance, since fluoranthene is known to be a hazardous environmental pollutant. The linear range was 25-150 ppb with the detection limit (3σ) of 6.3 ppb, and the recovery was in the range of 95-105 %. The proposed method shows an excellent characteristics of simple and accurate, which makes a new way for measuring organic pollutions at trace levels.3. Development of a novel potentiometric detector for FIAFIA has found widespread applications in analytical chemistry and biochemistry owing to its desirable characteristics, such as low consumption of reagents, high sample throughput, simple automated operation, and possibility of on-line sample pretreatment. Routine FIA measurements can be performed by using various detection methods. UV-absorption, fluorescence, amperometric and conductometric detectors have been commonly applied to analytes with chromophoric, fluorescent, electroactive and ionic properties. Potentiometric detectors are characterized by excellent selectivity, low cost, high reliability and ease of fabrication and miniaturization, which represent an attractive alternative to the conventional FIA detection modes. Conventional potentiometric FIA systems exploit direct measurements of analyte ions using the ISEs. To extend the applications of ISEs in FIA, the indirect sensing mode has been developed based on the complexing and redox properties of indicator ions. Many analytes can be indirectly measured by potentiometrically monitoring the reduction of indicator ions which are added in the carrier solution. Although these approaches have made great contributions toward the potentiometric detection in FIA, there are some inherent disadvantages including peak broadening resulting from the excessive volume introduced by the reaction coil and slow electrode response. Herein, we explore a promising detection system that makes use of outward ion fluxes through an ISE membrane (i.e., fluxes in the direction of the sample solution) to provide reagent-free detection. The ISE membrane not only serves as a polymer matrix for reagent release as used in the polymeric delivery systems, but also works as an transducer for sensitive potentiometric detection. As a proof-of-concept experiment, a polymeric membrane permanganate-selective electrode has been developed as a controlled reagent release system for potentiometric detection of ascorbate, dopamine and norepinephrine. Under the optimized conditions, the potential peak heights were proportional to the reductant concentrations in the ranges of 1.0×10-5 - 2.5×10-7 mol/L for ascorbate, of 1.0×10-5 - 5.0×10-7 mol/L for dopamine, and of 1.0×10-5 - 5.0×10-7 mol/L for norepinephrine, respectively with the corresponding detection limits of 7.8×10-8, 1.0×10-7 and 1.0×10-7 mol/L. To prove the generality of the detector, histidine, arginine, methionine, threonine, cysteine, valine and phenylalanine were also measured using a polymeric membrane copper-selective electrodes. The established method has been successfully applied for the real samples analysis.4. Development of a novel potentiometric detector for HPLCIn this work, we describe our initial efforts to extend the application of this novel ISE detection method metioned above to HPLC. Multicomponent detection in hydrodynamic HPLC systems requires a rapid recovery time of the detector to avoid the problem of peak tailing, which not only affects the measurement of peak height and area but also degrades the resolution of adjacent solutes. An external current at the nanoampere scale is applied across the ISE membrane for rapid and precise release of reagent, which addresses such limitations. Threonine, leucine, methionine phenylalanine and histidine can be baseline separated by reversed-phase chromatography. The detection limits (3σ) were 2.6×10-6 mol/L for threonine, 1.0×10-6 mol/L for leucine, 7.3×10-7 mol/L for methionine, 6.8×10-8 mol/L for histidine, 1.8×10-6 mol/L for phenylalanine. In contrast to the conventional detectors, the proposed potentiometric detector can monitor a wide range of analytes without chromophore and electrochemically active groups. |
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