Affinity capillary electrophoresis on microchips

The present study shows that the application of the method of affinity capillary electrophoresis (ACE) to investigate interactions between ligands and their substrates can be realized on microchips. With ACE it is possible to characterize non-covalent molecular interactions (complexation and partition equilibria). Binding constants (K(B)) provide a measured value of the affinity of a ligand molecule to a substrate, which is basic information for the understanding of hormones, drugs and their targets, e.g. receptors in the human body. A microchip electrophoresis instrument equipped with a UV-detector and a home-built chip-station with electrochemical detection were used. ACE could be achieved with model solutions of neurotransmitters using sulfated beta-cyclodextrin (sCD) as substrate in a background buffer. This paper describes the advantages of microchip-ACE (MC-ACE) to traditional affinity capillary electrophoresis on a capillary. The results show that MC-ACE has great potential as a tool for fast scanning of interactions and to calculate binding constants of ligands with their substrates.     

Wall coating for capillary electrophoresis on microchips

This review article with 116 references describes recent developments in the preparation of wall coatings for capillary electrophoresis (CE) on a microchip. It deals with both dynamic and permanent coatings and concentrates on the most frequently used microchip materials including glass, poly(methyl methacrylate), poly(dimethyl siloxane), polycarbonate, and poly(ethylene terephthalate glycol). Characterization of the channel surface by measuring electroosmotic mobility and water contact angle of the surface is included as well. The utility of the microchips with coated channels is demonstrated by examples of CE separations on these chips.     

Direct electrochemical determination of pyruvate in human sweat by capillary zone electrophoresis.

Capillary zone electrophoresis was employed for the determination of pyruvate in human sweat using electrochemical detection with a carbon fiber microdisk bundle electrode at a constant potential of 1.60 V vs. saturated calomel electrode. The optimum separation conditions are 3.6 x 10(-3) mol/L Na2HPO4-1.4 x 10(-3) mol/L NaH2PO4 (pH 7.2) for the buffer solution, and 18 kV for the separation voltage. The limits of detection of pyruvate are 8.0 x 10(-6) mol/L or 24 fmol (S/N = 3) for the injection voltage of 6 kV and the injection time of 10 s. The relative standard deviation is 2.0% for the migration time and 5.7% for the electrophoretic peak current. The method was applied to determining pyruvate in human sweat.     

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.     

Nonaqueous capillary electrophoresis with indirect electrochemical detection

Nonaqueous capillary electrophoresis (NACE) which makes use of organic solvents in place of conventional aqueous electrophoresis buffers is gaining increasing importance among modern separation techniques. Recently, it has been shown that amperometric detection in conjunction with acetonitrile-based NACE offers an extended accessible potential range and an enhanced long-term stability of the amperometric responses generated at solid electrodes. The present contribution takes advantage of the latter aspect to develop reliable systems for NACE with indirect electrochemical detection (IED). In this context, several compounds such as (ferrocenylmethyl)trimethylammonium perchlorate, tris(1,10-phenanthroline)cobalt(III) perchlorate and bis(1,4,7-triazacyclononane)nickel(II) perchlorate were studied regarding their suitability to act as electroactive buffer additives for IED in NACE. The performance characteristics for the respective buffer systems were evaluated. Tetraalkylammonium perchlorates served as model compounds for the optimization of the NACE-IED system. Target analytes choline and acetylcholine could easily be separated and determined by means of NACE-IED. In the case of a buffer system containing 10(-4) M tris(1,10-phenanthroline)cobalt(III) perchlorate the limits of detection were 2.5 x 10(-7) M and 4.6 x 10(-7) M for choline and acetylcholine, respectively. With the elaborated analytical procedure choline could be determined in pharmaceutical preparations.     

Amperometric detector designs for capillary electrophoresis microchips

Electrochemical (EC) detection is a sensitive and miniaturisable detection mode for capillary electrophoresis (CE) microchips. Detection cell design is very important in order to ensure electrical isolation from the high separation voltage. Amperometric detectors with different designs have been developed for coupling EC detection to CE-microchips. Different working electrode alignment: in-channel or end-channel has been tested in conjunction with several materials: gold, platinum or carbon. The end-channel detector was based on a platinum or gold wire manually aligned at the exit of the separation channel. Thick- (screen-printed carbon electrode) and thin-film (sputtered gold film) electrodes have also been employed with this configuration, but with a different design that allowed the rapid replacement of the electrode. The in-channel detector was based on a gold film within the separation channel. A gold-based dual electrode detector, which combined for the first time in- and end-channel detection, has been also tested. These amperometric detectors have been evaluated in combination to poly(methylmethacrylate) (PMMA) and Topas (thermoplastic olefin polymer of amorphous structure) CE-microchips. Topas is a new and promising cyclic olefin copolymer with high chemical resistance. Relevant parameters of the polymer microchip separation such as precision, efficiency or resolution and amperometric detection were studied with the different detector designs using p-aminophenol and L-ascorbic acid as model analytes in Tris-based buffer pH 9.0.     

Recent developments in electrochemical detection for microchip capillary electrophoresis

Significant progress in the development of miniaturized microfluidic systems has occurred since their inception over a decade ago. This is primarily due to the numerous advantages of microchip analysis, including the ability to analyze minute samples, speed of analysis, reduced cost and waste, and portability. This review focuses on recent developments in integrating electrochemical (EC) detection with microchip capillary electrophoresis (CE). These detection modes include amperometry, conductimetry, and potentiometry. EC detection is ideal for use with microchip CE systems because it can be easily miniaturized with no diminution in analytical performance. Advances in microchip format, electrode material and design, decoupling of the detector from the separation field, and integration of sample preparation, separation, and detection on-chip are discussed. Microchip CEEC applications for enzyme/immunoassays, clinical and environmental assays, as well as the detection of neurotransmitters are also described.     

Recent progress for capillary electrophoresis with electrochemical detection

Capillary electrophoresis (CE) is an attractive technique in separation science because of its high separation performance, short analysis time and low cost. Electrochemical detection (EC) is a powerful tool for CE because of its high sensitivity. In this review, developments of CE-EC from 2008 to August, 2011 are reviewed. We choose papers of innovative and novel results to demonstrate the newest and most important progress in CE-EC.      

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).     

A handy detection cell for end-column electrochemical detection in capillary electrophoresis.

A handy and simple detection cell was constructed using a mixing joint for end-column electrochemical detection in capillary electrophoresis (CE). The cell allows for positioning of the working electrode at the end of the separation capillary without the aid of micropositioners. The design facilitates the exchange of electrodes and capillaries without the need to refabricate the entire capillary-electrode setup. The cell can be assembled in a short period of time. Alignment with the joint screw proved to be reproducible for working electrodes of copper and gold. The advantages of reduced time and low cost make the device very attractive for the routine analysis of electroactive species, such as carbohydrates and their derivatives, purine bases and nucleosides, amino acids, and catecholamines etc. by CE with electrochemical detection.     

Quantitative determination of glutathione in single human erythrocytes by capillary zone electrophoresis with electrochemical detection

Glutathione (GSH) in single human erythrocytes is determined by capillary zone electrophoresis with end-column amperometric detection at a gold/mercury amalgam microelectrode. A capillary of 10 microm inner diameter is suitable for determination of GSH in an individual erythrocyte with a good signal-to-noise ratio. The limit of detection is 1 x 10(-7) mol/L or 26 amol and the linear dynamic range is 2 x 10(-7) to 2 X 10(-5) mol/L for the capillary. In this method, the calibration line is obtained with a capillary adsorbed before a certain amount of hemoglobin can be used for the quantification of GSH in the external standardization. The whole cell injection and the lack of necessity of a derivatization reaction lead to more accurate and precise results, which are closer to the macroscopic values of glutathione in human red blood cell (i.e., hemolysate) than those determined by indirect laser-induced fluorescence detection.     

Measurement of ascorbic acid in single human neutrophils by capillary zone electrophoresis with electrochemical detection

A method has been developed for the determination of ascorbic acid (AA) in individual human neutrophils by capillary zone electrophoresis with electrochemical detection at a carbon fiber microdisk bundle electrode. The natively easily oxidized substances such as glutathione, dopa, dopamine, serotonin, epinephrine do not interfere with the determination of ascorbic acid. A procedure of treating capillaries, which can overcome the influence of the adsorption of the substances in cells on the inner surface wall of the capillary on the migration time and the number of theoretical plates of interests, has been described. The average amount of AA in an individual neutrophil is 0.557 fmol, which is consistent with the literature value.     

Assay of amino acids in individual human lymphocytes by capillary zone electrophoresis with electrochemical detection

Amino acids in individual human lymphocytes were determined by capillary zone electrophoresis with electrochemical detection (ED) at a carbon fiber bundle electrode after on-column derivatization with naphthalene-2,3-dicarboxaldehyde (NDA) and CN⁻. In order to inject cells easily, a cell injector was designed. In this method, a single human lymphocyte and then the lysing/derivatizing buffer were electrokinetically injected into the front end of the separation capillary as a chamber to lyse the lymphocyte and derivatize amino acids in the cell. Four amino acids (serine (Ser), alanine (Ala), taurine (Tau), and glycine (Gly)) in single human lymphocytes have been identified. Quantitation has been accomplished through the use of calibration curves.     

Numerical simulation of electrokinetic injection techniques in capillary electrophoresis microchips

The effective design and control of a capillary electrophoresis (CE) microchip requires a thorough understanding of the electrokinetic transport phenomena associated with its microfluidic injection system. The present study utilizes a numerical simulation approach to investigate these electrokinetic transport processes and to study the control parameters of the injection process. Injection systems with a variety of different configurations are designed and tested, including the cross-form, T-form, double-T-form, variable-volume focused flow cross-form, and variable-volume triple-T-form configuration. Each injection system cycles through a predetermined series of steps in which the magnitudes and distributions of the applied electric field are precisely manipulated in order to effectuate a virtual valve. This study investigates the sample leakage effect associated with each of the injection configurations and applies the double-L, pullback, and focusing injection techniques to minimize the sample leakage effect. The injection methods presented in this paper have the exciting potential for use in high-quality, high-throughput chemical analysis applications and throughout the micro-total-analysis systems field.     

毛细管电泳-电化学检测法测定饲料中的磺胺类药物

采用毛细管电泳-电化学检测法(CE-ED),对饲料中的6种磺胺类药物磺胺脒、磺胺二甲嘧啶、磺胺甲嘧啶、磺胺二甲氧嘧啶、磺胺嘧啶、磺胺甲恶唑进行了分离和测定。分别考察了工作电极电位、运行缓冲液的pH和浓度、分离电压和进样时间等实验参数对实验结果的影响。在优化的实验条件下,以直径300μm的碳圆盘电极为工作电极,检测电位为0.95 V(vs.SCE),在30 mmol/L硼砂-KH2PO4(pH7.6)的运行缓冲溶液中,6个分析物能够在16 min内实现很好的基线分离,被测物浓度与峰电流在3个数量级呈良好的线性,检出限(S/N=3)范围0.08～0.20μg/mL。该方法已应用于实际样品的分析。     

毛细管电泳电化学检测法测定烟草中的多元酚

采用毛细管电泳电化学检测法同时测定了烟草中的多元酚,即芦丁、绿原酸,槲皮素和咖啡酸。考察了工作电极的氧化电位、运行缓冲溶液浓度和pH值,分离电压和进样时间对分离和检测的影响。在优化条件下,以300μm直径的碳圆盘电极为工作电极,检测电位为+0.9 V(vs.SCE),在50 mmol/L硼酸盐(pH 8.4)的运行缓冲液中,被测物浓度与峰电流在三个数量级范围内呈良好线性,检出限为2×10-7或5×10-7g/mL。方法有着良好的重现性,被测组分的迁移时间和峰高的相对标准偏差(RSDs)小于4%(n=7)。单次测定可在16 min内完成,已用于实际样品多元酚的测定,样品处理简单,无须预富集。     

Monitoring environmental pollutants by microchip capillary electrophoresis with electrochemical detection

During the past decade, significant progress in the development of miniaturized microfluidic systems has occurred due to the numerous advantages of microchip analysis. This review focuses on recent advances and the key strategies in microchip capillary electrophoresis (CE) with electrochemical detection (ECD) for separating and detecting a variety of environmental pollutants. The subjects covered include the fabrication of microfluidic chips, ECD, typical applications of microchip CE with ECD in environmental analysis, and future prospects. It is expected that microchip CE-ECD will become a powerful tool in the environmental field and will lead to the creation of truly portable devices.     

Multiple-channel microchips for high-throughput DNA analysis by capillary electrophoresis

Capillary electrophoresis on microfabricated multiple-channel chips has great potential for high-throughput analysis. This review focuses on multiple-channel chips used for high-throughput DNA analysis. It covers progress in the design and fabrication of multiple-channel chips and detection schemes used on these chips. Applications are concentrated on DNA fragment sizing, genotyping, and sequencing.     

Capillary electrophoresis and capillary flow injection analysis with electrochemical detection

Measurements by capillary flow injection analysis (CFIA) and capillary electrophoresis (CE) in conjunction with electrochemical detection are described. The detection is based on an end-column electrode arrangement. Several novel electrodes, such as a spherical gold electrode and a dual-microdisk electrode, are presented and characterized regarding their analytical utility. In order to improve the selectivity of CFIA, dual-electrode and multiple-pulse detection are studied using couples of cyanometallates or metallocenes. Capillary electrophoretic experiments with amperometric detection are performed using 50 m i.d. capillaries without any electrical-field decoupler. The practicality and analytical characteristics of this detection strategy are illustrated for the separation of serotonin and some biological precursors and metabolites of neurotransmitter substances.