Conductimetric and potentiometric detection in conventional and microchip capillary electrophoresis

Potentiometric detection is rarely used in separation methods but is promising for certain classes of analytes which can only with difficulty be quantified by more standard methods. Conductimetric detection of ions is very versatile and has recently received renewed interest spurned by the introduction of the capacitively coupled contactless configuration. Both are useful and complementary alternatives to the established optical detection methods, and to the more widely known electrochemical method of amperometry. The simplicity of the electrochemical methods makes them particularly attractive for microfabricated devices, but relatively little work has to date been carried out with regard to potentiometric and conductimetric detection.     

Conductivity detection in capillary electrophoresis

Among electrochemical detection methods in capillary electrophoresis, conductometric methods are of specific interest for the determination of inorganic species. This is due to the fact that inorganic ions exhibit a high equivalent conductivity which corresponds to the analytical signal in conductivity detection. Indirect optical absorption methods, which are widely used in capillary electrophoretic ion analyses, become less sensitive with smaller capillary dimensions and thus have disadvantages in electrokinetic chip separation technologies.Conductivity detection for capillary electrophoresis is performed either through galvanic contact or in a contactless mode. Techniques using a galvanic contact of the sample ions with the measuring electrode are performed either on-capillary without decoupling of the separation high voltage, or off-capillary after grounding the separation voltage in order to avoid interferences. This technology is specifically important when a suppressor is used prior to detection. Most contactless methods use oscillometric techniques in order to obtain the analytical signal.This review discusses the theoretical and instrumental background of conductivity detection in capillary electrophoresis and reports on recent aspects and applications using conductometric detection methods for capillary zone electrophoresis.     

Determination of amino acid neurotransmitters in human cerebrospinal fluid and saliva by capillary electrophoresis with laser-induced fluorescence detection

A CE-LIF detection method has been developed to identify and quantitate six amino acid neurotransmitters including glutamic acid, aspartic acid, gamma-aminobutyric acid, glycine, taurine, and glutamine. N-hydroxysuccinimidyl fluorescein-O-acetate, a fluorescein-based dye, was employed for the derivatization of these neurotransmitters prior to CE-LIF analysis. Different parameters which influenced separation and derivatization were optimized in detail. Under optimum conditions, linearity was achieved within concentration ranges of up to three orders of magnitudes for those analytes with correlation coefficients from 0.9989 to 0.9998. The LODs ranged from 0.06 nM to 0.1 nM, and are thus superior or equivalent to those previously reported in the literature using CE-LIF detection. The proposed method has been successfully applied to the determination of amino acid neurotransmitters in biological samples such as human cerebrospinal fluid and saliva with satisfactory recoveries.     

Evaluation of the detection of biomolecules in capillary electrophoresis by contactless conductivity measurement

The sensitivity of contactless conductivity detection to amino acids, peptides and proteins in CE was studied for BGE solutions of different pH values. The LOD and analytical characteristics were compared for acidic and basic conditions and better results were in most cases found for buffers of low pH values. Linear dynamic ranges varied between two orders of magnitude for amino acids and peptides and three orders of magnitude for larger proteins. The concentration detection limits were found to be between 1.2 and 7.5 microM for the amino acids tested and for the larger molecules they varied between 2.6 microM for leucine enkephalin and 0.2 microM for HSA when using a buffer at pH 2.1.     

毛细管电泳荧光检测模式的研究进展

毛细管电泳技术由于具有分析速度快、分离效率高、样品用量少、操作简单、抗污染能力强等特点,广泛的应用于环境监测、临床检验、生物样品分析等领域.荧光检测技术的引入使毛细管电泳在保持强大的分离能力的同时具有了较高的检测灵敏度.本文介绍了影响毛细管电泳-荧光检测灵敏度的两个重要因素(光源和检测模式),对目前常用的两种光源(激光和发光二极管)以及三种检测模式的光路结构(正交型、共线型和嵌入式光纤传导-柱内直接激发型)的设计进行了相应地比较.     

毛细管电泳和毛细管电色谱技术在农药残留检测中的应用

由于毛细管电泳（CE）和毛细管电色谱（CEC）具有所需样品体积小、分离效率高等特点,越来越多的学者已将它们应用到农药残留（简称农残）检测中,并将它们同各种不同的检测器以及样品浓缩方法相结合,以提高检测的灵敏度。本文对CE和CEC两种方法中所涉及的常见的样品预浓缩方法进行了简要的介绍。对各种不同类型的检测器（如紫外检测、荧光检测、电化学检测以及质谱检测等）的优缺点及其在农残检测中的应用情况进行了评述;同时对手性农药的CE和CEC分离检测情况进行了特别介绍;并对CE和CEC在农残分析与检测中的应用前景进行了展望。     

Label-free fluorescence detection in capillary and microchip electrophoresis

Herein, we summarize the current status of native fluorescence detection in microchannel electrophoresis, with a strong focus on chip-based systems. Fluorescence detection is a powerful technique with unsurpassed sensitivity down to the single-molecule level. Accordingly fluorescence detection is attractive in combination with miniaturised separation techniques. A drawback is, however, the need to derivatize most analytes prior to analysis. This can often be circumvented by utilising excitation light in the UV spectral range in order to excite intrinsic fluorescence. As sensitive absorbance detection is challenging in chip-based systems, deep-UV fluorescence detection is currently one of the most general optical detection techniques in microchip electrophoresis, which is especially attractive for the detection of unlabelled proteins. This review gives an overview of research on native fluorescence detection in capillary (CE) and microchip electrophoresis (MCE) between 1998 and 2008. It discusses material aspects of native fluorescence detection and the instrumentation used, with particular focus on the detector design. Newer developments, featured techniques, and their prospects in the future are also included. In the last section, applications in bioanalysis, drug determination, and environmental analysis are reviewed with regard to limits of detection.     

Near-infrared laser-induced fluorescence detection in capillary electrophoresis

As capillary electrophoresis continues to focus on miniaturization, either through reducing column dimensions or situating entire electrophoresis systems on planar chips, advances in detection become necessary to meet the challenges posed by these electrophoresis platforms. The challenges result from the fact that miniaturization requires smaller load volumes, demanding highly sensitive detection. In addition, many times multiple targets must be analyzed simultaneously (multiplexed applications), further complicating detection. Near-infrared (NIR) fluorescence offers an attractive alternative to visible fluorescence for critical applications in capillary electrophoresis due to the impressive limits of detection that can be generated, in part resulting from the low background levels that are observed in the NIR. Advances in instrumentation and fluorogenic labels appropriate for NIR monitoring have led to a growing number of examples of the use of NIR fluorescence in capillary electrophoresis. In this review, we will cover instrumental components used to construct ultrasensitive NIR fluorescence detectors, including light sources and photon transducers. In addition, we will discuss various types of labeling dyes appropriate for NIR fluorescence and finally, we will present several applications that have used NIR fluorescence in capillary electrophoresis, especially for DNA sequencing and fragment analysis.     

Amperometric and voltammetric detection for capillary electrophoresis

The focus of this article is amperometric and voltammetric detection coupled with capillary electrophoresis. Fundamental concepts and progress in the field of capillary electrophoresis with electrochemical detection (CEEC) that have occurred within the past three years, including new methodologies and unique applications, are highlighted. This review contains 95 references.     

Microchip capillary electrophoresis with a cellulose-DNA-modified screen-printed electrode for the analysis of neurotransmitters

A microfluidic chip based on capillary electrophoresis coupled with a cellulose-single-stranded DNA (cellulose-ssDNA) modified electrode was used for the simultaneous analysis of dopamine (DA), norepinephrine (NE), 3,4-dihydroxy-L-phenylalanine (L-DOPA), 3,4-dihydroxyphenylacetic acid (DOPAC), and ascorbic acid (AA). The modification of the electrode improved the electrophoretic analysis performance by lowering the detection potential and enhancing the signal-to-noise characteristic without surface poisoning of the electrode. The sensitivity of the modified electrode was about 12 times higher than those of the bare ones. The test compounds were separated using a 62 mm long separation channel at the separation field strength of +200 V/cm within 220 s in a 10 mM phosphate buffer (pH 7.4). The most favorable potential for the amperometric detection was 0.7 V (vs. Ag/AgCl). A reproducible response (relative standard deviation of 1.3, 1.3, 2.1, 3.1, 3.4% for DA, NE, L-DOPA, DOPAC, and AA, respectively, for n = 9) for repetitive sample injections reflected the negligible electrode fouling at the cellulose-ssDNA modified electrode. Square-wave voltammetric analyses reflected the sensitivities of the modified electrode for DA, NE, L-DOPA, DOPAC, and AA which were 1.78, 0.82, 0.69, 2.45, and 1.23 nC/microM with detection limits of 0.032, 0.93, 1.13, 0.31, and 0.62 microM, respectively. The applicability of this microsystem to real sample analysis was demonstrated.     

Evaluation of the inhibition of choline uptake in synaptosomes by capillary electrophoresis with electrochemical detection

A direct method for evaluating choline uptake by the high-affinity choline transport system in synaptosomes was developed using capillary electrophoresis (CE) with electrochemical (EC) detection. On-column EC detection of choline and the internal standard, butyrylcholine, was accomplished with a 25 microm platinum electrode modified with the enzymes, choline oxidase and acetylcholinesterase. Choline uptake was evaluated as a function of choline concentration and a KM value of 1.7 microM was determined. The method was also used to evaluate a new class of redox affinity inhibitors of choline transport. In particular, the effectiveness of 3-[(trimethylammonio)methyl]catechol (TMC) as an inhibitor of choline uptake was examined independently and relative to the inhibition of the well-known inhibitor of choline transport, hemicholinium-3. The IC50 and KI for TMC were determined to be 30 microM and 14 microM, respectively. The combination of the selectivity and sensitivity afforded by CEEC provides a relatively straightforward approach for monitoring choline transport in synaptosomes.     

Chemiluminescence detection coupled to capillary electrophoresis

In recent years, chemiluminescence (CL)-based detection coupled to capillary electrophoresis (CE) as separation technique has attracted much interest due to new advances in home-made configurations, sample-treatment techniques for application to real matrixes, development of a commercial instrument and use of miniaturization techniques to obtain micro total analysis systems incorporating CE separation and CL detection in microchips. We present some developments, key strategies and selected analytical applications of CE-CL since the year 2000 in diverse fields (e.g., clinical and pharmaceutical, environmental or food analysis).     

Indirect photometric detection in capillary zone electrophoresis

An indirect photometric detection method is described which is based on the use of an absorbing co-ion as the principal component of the background electrolyte. The zones of non-absorbing ionic species are revealed by changes in light absorption due to charge displacement of the absorbing co-ion. Theoretical considerations are given for selecting a suitable absorbing co-ion to achieve a high sensitivity of detection.The role of electromigration dispersion is illustrated by experiments and the effects of the differences in the effective mobilities of sample ions and that of the absorbing co-ion are discussed. The highest sensitivity can be achieved for sample ions having an effective mobility close to the mobility of the absorbing co-ion. In such a case, the concentration of the sample component in its migrating zone can be high while electromigration dispersion is still negligible. The useful dynamic range of the detection is then limited by the linearity and noise of the detector, the former parameter being given mostly by the shape of the on-column detection cell. The best sensitivities can be obtained in low-concentration background electrolytes containing a co-ion with high absorption at a given detection wavelength.It is shown that indirect photometric detection can be useful for detecting substances that have no optical absorption in the UV and/or visible region, provided that the composition of the background electrolyte is selected correctly.     

Indirect thermo-optical detection for capillary electrophoresis

Indirect thermo-optical detection for capillary electrophoresis is described first. A 20 mW helium-neon laser (632.8 nm) was used to provide the pumping beam and a 2 mW helium-neon laser (632.8 nm) supplied as the probe beam; Methylene Blue dye was used as a background absorber. The addition of ethanol to the background electrolyte solution can be performed to reduce adsorption of Methylene Blue onto the capillary wall. The detection method was applied to the detection of amino acids separated by capillary electrophoresis. The detection limit for lysine was 5 × 10⁻⁶ mol l⁻¹ (signal-to-noise ratio, 2).     

毛细管电泳多道电化学检测工作站

设计的毛细管电泳多通道电化学检测系统是一个可供在同一个检测环境下，用多台电化学检测器循环对物质进行测定的工作站。工作站采用计算机控制，利用电导和伏安检测器对样品同时进行电导、氧化和还原检测，并实时对数据进行采集，处理，以图形方式显示。     

Capillary electrophoresis and microchip capillary electrophoresis with electrochemical and electrochemiluminescence detection

Recent advances and key strategies in capillary electrophoresis and microchip CE with electrochemical detection (ECD) and electrochemiluminescence (ECL) detection are reviewed. This article consists of four main parts: CE-ECD; microchip CE-ECD; CE-ECL; and microchip CE-ECL. It is expected that ECD and ECL will become powerful tools for CE microchip systems and will lead to the creation of truly disposable devices. The focus is on papers published in the last two years (from 2005 to 2006).     

Separation and detection of lanthanides by capillary electrophoresis

Due to the importance of application of lanthanides in various industries especially the nuclear ones, and the advantages of capillary electrophoresis method in separation of metal cations, this research was carried out in order to investigate the separation potential of lanthanides using capillary electrophoresis via simulation method at laboratory scale. Since the properties of various types of lanthanides are very similar, the separation of lanthanides using the usual approaches was not possible. Thus, the separation of lanthanides was devised upon partial, competing complexation in order to differentiate their properties. Salicylic acid was firstly used as the primary UV-absorbing ligand, whereas formic, acetic, lactic, tartaric and citric acids, which showed no absorption in UV-spectrum and had weaker complexes in comparison to salicylic acid, were used as auxiliary ligands. Upon the results of spectrometry, the wave length of 210 nm was selected for detecting lanthanides. The properties and stability of lanthanides were examined and furthermore acetic and citric acids were selected as auxiliary ligands. The simulation was carried out with respect to the transport phenomena in the unsteady state. The ion species dissociation was found to be directly dependent upon the concentration, and was also used in complexation. The results of simulation showed that the diffusion control of H⁺ and homogenizing electrical field promoted separation quality. The separation conditions were optimized by using the simulation results as well as the tests obtained. In order to optimize the experimental conditions, variable factors such as voltage, injection time, pH, temperature and ionic strength were examined. Also, methanol was used as dissolving modifier as well as noise reducer on the base line. Sodium nitrate was used as ionic strength controller and sucrose for increasing viscosity which optimized separation quality.     

Recent advances in electrochemical detection in capillary electrophoresis

Recent advances in the design and application of electrochemical (EC) detection systems in capillary electrophoresis (CE) are reviewed, with the objective of providing the nonelectrochemist with a state-of-the-art picture of CEEC instrumentation and an overview of the principal analytes for which CEEC is best suited. The detection schemes considered here include those based both on amperometry and on potentiometry as both kinds of EC systems are being actively developed in CE and have the potential for broad application in analysis. Over the three-year period covered by this review, an important direction that CEEC has taken is the construction of more complex electrode systems beginning with the use of multiple EC electrodes and culminating with the adaptation of EC detection to microfabricated "lab-on-a-chip" analysis devices. In addition, CEEC applications have now grown to include a broad variety of inorganic, organic, and biochemical analytes and samples.