Determination of tea catechins

An overview of analytical methods for the measurement of biologically important tea catechins is presented. Liquid chromatography and capillary electrophoresis are the most cited techniques for catechin separation, identification and quantitation. Liquid chromatography with ultraviolet detection is frequently used; however, mass spectrometry, electrochemical, fluorescence and chemiluminescence detection are also utilized in cases where more sensitive or selective detection is needed. Two modes of capillary electrophoresis, capillary zone electrophoresis and micellar electrokinetic capillary chromatography, have been employed for the determination of catechins. Both modes of capillary electrophoresis are based on ultraviolet detection. Additional analytical techniques, such as gas chromatography, thin-layer chromatography, paper chromatography, spectrophotometry, biosensing, chemiluminescence and nuclear magnetic resonance spectroscopy have also been utilized for the determination of catechins and are reviewed herein.     

Combining capillary electrophoresis with mass spectrometry for applications in proteomics

Mass spectrometry (MS)-based proteomics is currently dominated by the analysis of peptides originating either from digestion of proteins separated by two-dimensional gel electrophoresis (2-DE) or from global digestion; the simple peptide mixtures obtained from digestion of gel-separated proteins do not usually require further separation, while the complex peptide mixtures obtained by global digestion are most frequently separated by chromatographic techniques. Capillary electrophoresis (CE) provides alternatives to 2-DE for protein separation and alternatives to chromatography for peptide separation. This review attempts to elucidate how the most promising CE modes, capillary zone electrophoresis (CZE) and capillary isoelectric focusing (CIEF), might best be applied to MS-based proteomics. CE-MS interfacing, mass analyzer performance, column coating to minimize analyte adsorption, and sample stacking for CZE are considered prior to examining numerous applications. Finally, multidimensional systems that incorporate CE techniques are examined; CZE often finds use as a fast, final dimension before ionization for MS, while CIEF, being an equilibrium technique, is well-suited to being the first dimension in automated fractionation systems.     

Selectivity in capillary electrokinetic separations

This review gives a survey of selectivity modes in capillary electrophoresis separations in pharmaceutical analysis and bioanalysis. Despite the high efficiencies of these separation techniques, good selectivity is required to allow quantitation or identification of a particular analyte. Selectivity in capillary electrophoresis is defined and described for different separation mechanisms, which are divided into two major areas: (i) capillary zone electrophoresis and (ii) electrokinetic chromatography. The first area describes aqueous (with or without organic modifiers) and nonaqueous modes. The second area discusses all capillary electrophoretic separation modes in which interaction with a (pseudo)stationary phase results in a change in migration rate of the analytes. These can be divided in micellar electrokinetic chromatography and capillary electrochromatography. The latter category can range from fully packed capillaries, via open-tubular coated capillaries to the addition of microparticles with multiple or single binding sites. Furthermore, an attempt is made to differentiate between methods in which molecular recognition plays a predominant role and methods in which the selectivity depends on overall differences in physicochemical properties between the analytes. The calculation of the resolution for the different separation modes and the requirements for qualitative and quantitative analysis are discussed. It is anticipated that selectivity tuning is easier in separation modes in which molecular recognition plays a role. However, sufficient attention needs to be paid to the efficiency of the system in that it not only affects resolution but also detectability of the analyte of interest.     

毛细管电泳在手性氨基酸拆分中的研究进展

毛细管电泳(capillary electrophoresis,CE)作为一种强有力的手性分离技术,由于操作简单、试剂消耗少及柱效高等优点,受到广泛关注,是近年来手性分离领域的研究热点.氨基酸是组成蛋白质的基本单元,且大多数氨基酸具有手性中心,手性氨基酸是生命体系的一个重要特征.具有手性中心的氨基酸,其对映体间的生物活性往往存在着较大的差异,因此,氨基酸的手性拆分对了解人体及动物生命活动起着举足轻重的作用.主要总结了近5年来毛细管电泳的3种分离模式(毛细管区带电泳、胶束电动毛细管色谱、毛细管电色谱)在氨基酸手性拆分中的发展和应用.     

Capillary electrophoretic methods for quality control analyses of pharmaceuticals: A review

Capillary electrophoresis represents a promising technique in the field of pharmaceutical analysis. The presented review provides a summary of capillary electrophoretic methods suitable for routine quality control analyses of small molecule drugs published since 2015. In total, more than 80 discussed methods are sorted into three main sections according to the applied electroseparation modes (capillary zone electrophoresis, electrokinetic chromatography, and micellar, microemulsion, and liposome-electrokinetic chromatography) and further subsections according to the applied detection techniques (UV, capacitively coupled contactless conductivity detection, and mass spectrometry). Key parameters of the procedures are summarized in four concise tables. The presented applications cover analyses of active pharmaceutical ingredients and their related substances such as degradation products or enantiomeric impurities. The contribution of reported results to the current knowledge of separation science and general aspects of the practical applications of capillary electrophoretic methods are also discussed.     

Pharmaceutical applications of micelles in chromatography and electrophoresis

This review surveys the use of micelles as separation media in chromatography and electrophoresis. Applications to pharmaceuticals whose molecular masses are relatively small are focused on in this review. In high-performance liquid chromatography (HPLC), chromatography using micelles and reversed-phase stationary phases such as octadecylsilylized silica gel (ODS) columns is known as micellar liquid chromatography (MLC). The main application of MLC to pharmaceutical analysis is the same as in ion-pair chromatography using alkylsulfonate or tetraalkylammonium. In most cases, selectivity is much improved compared with other short alkyl chain ion-pairing agents such as pentanesulfonate or octanesulfonate. Direct plasma/serum injection can be successful in MLC. Separation of small ions is also successful by using gel filtration columns and micellar solutions. In electrophoresis, especially capillary electrophoresis (CE), micelles are used as pseudo-stationary phases in capillary zone electrophoresis (CZE). This mode is called micellar electrokinetic chromatography (MEKC). Most of the drug analysis can be performed by using the MEKC mode because of its wide applicability. Enantiomer separation, separation of amino acids and closely related peptides, separation of very complex mixtures, determination of drugs in biological samples etc. as well as separation of electrically neutral drugs can be successfully achieved by MEKC. Microemulsion electrokinetic chromatography (MEEKC), in which surfactants are also used in forming the microemulsion, is successful for the separation of electrically neutral drugs as in MEKC. This review mainly describes the typical applications of MLC and MEKC for the analysis of pharmaceuticals.     

On-line capillary electrophoresis-mass spectrometry for the analysis of biomolecules

Mass spectrometry (MS) has become a key tool for the characterization of biologically relevant molecules in the last decade. Due to the complexity of most biological samples an upstream separation is essential. Capillary electrophoresis (CE) has gained much interest due to its high separation efficiency, speed, and often complementary selectivity to liquid chromatography. We describe the state-of-the-art of on-line CE-MS for the analysis of molecules of biological origin. The characterization of peptides, including the study of post-translational modifications, intact proteins, oligonucleotides, and related interaction studies are reviewed. Relevant publications are summarized in tables, including some important method parameters. Key applications are discussed with respect to the advantages and limitations of CE-MS. Coupling interfaces, preconcentration techniques, capillary coatings, and the different CE techniques, e.g., capillary zone electrophoresis, capillary isoelectric focusing, capillary gel electrophoresis, etc. are briefly discussed against the background of their bioanalytical applications.     

毛细管电泳新型手性分离体系研究进展

在现代分离科学中,手性化合物的分离分析一直是研究的重点和难点。相比于高效液相色谱（HPLC）、气相色谱（GC）等传统色谱分析方法,毛细管电泳（CE）技术凭借其高效率、低消耗、分离模式多样化等诸多优势,已经发展成为手性分离研究领域最有应用前景的分析方法之一。近年来,研究人员在CE手性分析方法的构建过程中,基于毛细管电动色谱（EKC）、配体交换毛细管电泳（LECE）、毛细管电色谱（CEC）等各种基础电泳模式,不断地对传统手性分离体系进行优化和改造,构建出了许多高性能的新型手性CE分离体系。如利用各类功能化离子液体以"手性离子液体协同拆分""手性离子液体配体交换""离子液体手性选择剂"等模式设计出多种基于离子液体的CE手性分离体系;利用纳米材料独特的尺寸效应、多样性、可设计性等特点,直接或与传统手性选择剂有机结合构建CE手性分离体系。此外,金属有机骨架材料修饰、低共熔溶剂修饰、非连续分段式部分填充等各式新颖的CE手性分离体系也都被研究人员成功开发,并表现出较大的发展潜力。该综述将对近年来（尤其是2015~2019年）此类新型CE手性分离体系的发展状况进行梳理,并结合相应的手性识别机理研究和手性CE方法实际应用情况,对该领域存在的问题及发展前景进行分析和展望。     

A decade of capillary electrophoresis

Since the introduction of the first commercial capillary electrophoresis (CE) instrument a decade ago, CE applications have become widespread. Today, CE is a versatile analytical technique which is successfully used for the separation of small ions, neutral molecules, and large biomolecules and for the study of physicochemical parameters. It is being utilized in widely different fields, such as analytical chemistry, forensic chemistry, clinical chemistry, organic chemistry, natural products, pharmaceutical industry, chiral separations, molecular biology, and others. It is not only used as a separation technique but to answer physicochemical questions. In this review, we will discuss different modes of CE such as capillary zone electrophoresis, micellar electrokinetic chromatography, capillary gel electrophoresis, capillary isoelectric focusing, and capillary electrochromatography, and will comment on the future direction of CE, including array capillary electrophoresis and array microchip separations.     

Methodological Challenges of Protein Analysis in Blood Serum and Cerebrospinal Fluid by Capillary Electrophoresis

Summary High-performance capillary electrophoresis (HPCE or CE) is an ultrasensitive analytical technique with high resolving power and a wide area of applications including peptide/protein analysis. Its applicability is greatly enhanced by the short separation times, the ease of method development and the minimum sample and organic solvent requirements. Various HPCE modes have been developed for peptide/protein analysis, including capillary zone electrophoresis, micellar elektrokinetic capillary chromatography, capillary isoelectric focusing, isotachophoresis, capillary gel electrophoresis and microemulsion elektrokinetic chromatography. HPCE can easily be applied to quality control of manufacturing processes or to clinical routine for diagnostic purposes due to its potential to provide information on the identity, the purity of the samples and the quantities of the constituents. Furthermore, interactions of a peptide or a protein with other molecules can be studied by HPCE. The separation principles of the various operation modes applied to peptide/protein analysis are presented in this article. Furthermore, in order to exemplify the application of the separation principles in the area of serum protein analysis, which is of importance in clinical practice, the capillary electrophoretic methods developed for analysis of serum and cerebrospinal fluid proteins are also reviewed.Presented at: International Symposium on Separation and Characterization of Natural and Synthetic Macromolecules, Amsterdam, The Netherlands, February 5–7, 2003     

Capillary electrophoresis of inorganic anions

This review deals with the separation mechanisms applied to the separation of inorganic anions by capillary electrophoresis (CE) techniques. It covers various CE techniques that are suitable for the separation and/or determination of inorganic anions in various matrices, including capillary zone electrophoresis, micellar electrokinetic chromatography, electrochromatography and capillary isotachophoresis. Detection and sample preparation techniques used in CE separations are also reviewed. An extensive part of this review deals with applications of CE techniques in various fields (environmental, food and plant materials, biological and biomedical, technical materials and industrial processes). Attention is paid to speciations of anions of arsenic, selenium, chromium, phosphorus, sulfur and halogen elements by CE.     

Application of micellar electrokinetic chromatography to pharmaceutical analysis

Electrokinetic chromatography is a new type of analytical separation method which belongs to the group of high performance capillary electrophoretic techniques but whose separation principle is based on that of chromatography. The solute distributes itself between a carrier and the surrounding medium. The carrier, which corresponds to the stationary phase in conventional chromatography, can be transported by electrophoresis with a different velocity from the surrounding medium. The separation is achieved by the differential solute distribution and the differential migration of the carrier. The charged molecules or charged molecular aggregates are employed as the carrier. Various kinds of carriers are available for electrokinetic chromatography along with different partition mechanisms. Among them, micellar electrokinetic chromatography, which employs an ionic micelle as a carrier, has become the most popular method because of its unique and attractive characteristics as well as the separating capability of electrically neutral or nonionic solutes in comparison with capillary zone electrophoresis. The present paper describes the principle, separation characteristics and its application to the analysis of pharmaceuticals.     

Recent progress in chiral separation principles in capillary electrophoresis

This review summarizes recent developments in the field of chiral separations by electromigration techniques including capillary zone electrophoresis (CZE), capillary gel electrophoresis (CGE), isotachophoresis (ITP), electrokinetic chromatography (EKC), and capillary electrochromatography (CEC). This overview focuses on the development of new chiral selectors and the introduction of new techniques rather than applications of already established selectors and methods. The mechanisms of the different chiral separation principles are discussed.     

微流控芯片二维电泳研究进展

综述了微流控芯片二维电泳技术及其在生命科学中的应用,包括胶束电动力学毛细管色谱(MEKC)与毛细管区带电泳(CZE)、等电聚焦(IEF)与CZE、开管电色谱(OCEC)与CZE耦联等模式的二维微流控芯片。展望了二维微流控芯片的应用前景。     

Recent Applications of Capillary Electrophoresis in the Determination of Active Compounds in Medicinal Plants and Pharmaceutical Formulations

The present review summarizes scientific reports from between 2010 and 2019 on the use of capillary electrophoresis to quantify active constituents (i.e., phenolic compounds, coumarins, protoberberines, curcuminoids, iridoid glycosides, alkaloids, triterpene acids) in medicinal plants and herbal formulations. The present literature review is founded on PRISMA guidelines and selection criteria were formulated on the basis of PICOS (Population, Intervention, Comparison, Outcome, Study type). The scrutiny reveals capillary electrophoresis with ultraviolet detection as the most frequently used capillary electromigration technique for the selective separation and quantification of bioactive compounds. For the purpose of improvement of resolution and sensitivity, other detection methods are used (including mass spectrometry), modifiers to the background electrolyte are introduced and different extraction as well as pre-concentration techniques are employed. In conclusion, capillary electrophoresis is a powerful tool and for given applications it is comparable to high performance liquid chromatography. Short time of execution, high efficiency, versatility in separation modes and low consumption of solvents and sample make capillary electrophoresis an attractive and eco-friendly alternative to more expensive methods for the quality control of drugs or raw plant material without any relevant decrease in sensitivity.     

Capillary electrophoresis on microchip

Capillary electrophoresis and related techniques on microchips have made great strides in recent years. This review concentrates on progress in capillary zone electrophoresis, but also covers other capillary techniques such as isoelectric focusing, isotachophoresis, free flow electrophoresis, and micellar electrokinetic chromatography. The material and technologies used to prepare microchips, microchip designs, channel geometries, sample manipulation and derivatization, detection, and applications of capillary electrophoresis to microchips are discussed. The progress in separation of nucleic acids and proteins is particularly emphasized.     

不同缓冲体系对毛细管电泳法分离15种核苷类化合物效果的比较

对毛细管电泳法分离15种核苷类化合物所用的不同缓冲液体系进行了系统比较,确定不同模式毛细管电泳法分析多种核苷类化合物的最适合背景缓冲液体系(BGE)。分别以四硼酸钠、磷酸氢二钠、乙酸钠、碳酸氢钠、乙酸铵和乙二胺(DEA)为背景电解质,对毛细管区带电泳(CZE)、毛细管电泳-电喷雾飞行时间质谱(CE-ESI-TOF/MS)以及胶束电动毛细管电泳(MEKC)3种模式进行比较,并对其中几种优势缓冲体系进行了优化。结果表明,CZE模式下使用四硼酸钠和磷酸氢二钠缓冲体系无法同时分离15种核苷类化合物,因此只适用于分析核苷类化合物数量较少的样品。而使用含有2%丙酮的300 mmol/L DEA能完全分开15种核苷类化合物,且分辨率和峰形良好。MEKC模式下,以25 mmol/L磷酸氢二钠(添加70 mmol/L十二烷基磺酸钠(SDS))为缓冲盐的分离结果最佳,并且此方法能成功应用于海洋生物海葵中核苷类化合物的分离。CE-ESI-TOF/MS分析中,以20 mmol/L乙酸铵(pH 10.0)为背景电解质,正离子模式检测,15种核苷类化合物的质谱信号均良好,检测灵敏度明显优于文献中报道的使用DEA缓冲体系的结果。本研究阐明了不同缓冲体系对15种核苷类化合物分离的适用性,为毛细管电泳技术在复杂基质中多种核苷类化合物的分离方法中的应用奠定了基础。