Separation of crystal violet dyes and its application to pen ink analysis using CZE and MEKC methods

A crystal violet (CV) standard was irradiated under a Hg-Cd lamp for different exposure times to obtain various N-demethylation products. CZE effectively separated the photodegradation products based on molecular weight differences. In contrast, micellar EKC (MEKC), using SDS as the surfactant, was ineffective because the binding constants of the demethylation products and SDS were too close for separation. Nevertheless, MEKC analysis of ink has applications in forensic science because MEKC separated neutral components in the inks. Thus, MEKC can be used to obtain an ink "fingerprint" since each ink is unique depending on the location and time it was made. In contrast, CZE is useful for dating inks because CV is the primary ink dye and it photodegrades slowly.     

Advances in chiral separation using capillary electromigration techniques

This review gives an overview of recent developments in CZE, EKC, and CEC covering the literature since the year 2004. Since there appeared a special issue on applications, this review focuses on the progress in electromigration techniques and new methodological developments. New techniques, new chiral selectors as well as new chiral stationary phases for CEC are discussed.     

Recent advances in chiral separation principles in capillary electrophoresis and capillary electrochromatography

This review summarizes recent developments in chiral separation in capillary zone electrophoresis (CZE), electrokinetic chromatography (EKC), and capillary electrochromatography (CEC) covering literature published since the year 2000. New chiral selectors and innovative approaches for CE and CEC are introduced. Recent progress in column technology for CEC is highlighted and the development of new chiral stationary phases is discussed. This review is not dedicated to list applications but will focus on new developments.     

Sweeping of neutral analytes via complexation with borate in capillary zone electrophoresis

Summary The sweeping concept is extended to capillary zone electrophoresis (CZE) separation of neutral solutes involving complexation with borate. Analogous to the pseudostationary phase in electrokinetic chromatography (EKC), the complexing agent (borate) serves as carrier for sweeping and separation in CZE. Therefore, similar to the retention factor in EKC, the focusing effect in the present system is directly related to the association constant between the analyte and complexing agent. Theoretical and some preliminary experimental studies gerenally suggest that the electrophoretic mobility of the complex and the concentration of the complexing agent affect the resulting length of narrowed zones. Moreover, sweeping using borate is affected by pH since borate complexation is pH dependent. From around 10 to 40-fold improvement in peak heights has been observed experimentally for some neutral test analytes (monosaccharides, catechols, and nucleosides)     

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.     

Recent advances in the development and application of microemulsion EKC

Microemulsion EKC (MEEKC) is an electrodriven separation technique. Separations are typically achieved using oil-in-water microemulsions, which are composed of nanometre-sized oil droplets suspended in an aqueous buffer. The droplets are stabilised by a surfactant and a cosurfactant. The novel use of water-in-oil microemulsions has also been investigated. This review summarises the advances in the development of MEEKC separations and also the different areas of application including determination of log P values, pharmaceutical applications, chiral analysis, natural products and bioanalytical separations and the use of new methods such as multiplexed MEEKC and high speed MEEKC. Recent applications (2004-2006) are tabulated for each area with microemulsion composition details.     

Supercritical fluid extraction: Recent advances and applications

Among the different extraction techniques used at analytical and preparative scale, supercritical fluid extraction (SFE) is one of the most used. This review covers the most recent developments of SFE in different fields, such as food science, natural products, by-product recovery, pharmaceutical and environmental sciences, during the period 2007–2009. The revision is focused on the most recent advances and applications in the different areas; among them, it is remarkable the strong impact of SFE to extract high value compounds from food and natural products but also its increasing importance in areas such as heavy metals recovery, enantiomeric resolution or drug delivery systems.     

Chromatographic and electrophoretic approaches for the analysis of protein quality of soy beverages

Furosine, generated by acid hydrolysis of fructosyllysine, an early Maillard reaction product, is a highly valuable indicator of food quality and, more specifically, of food protein quality. Ion pair RP-HPLC and CZE techniques were employed to determine furosine content in beverages based on soymilk (n = 15) and cow's milk supplemented with soy isoflavones (n = 1). The levels of furosine found in the samples ranged from 25.55 +/- 0.18 to 170.72 +/- 10.4 mg/100 g of protein by HPLC and from 28.67 +/- 1.84 to 161.25 +/- 5.78 mg/100 g of protein by CZE. Results obtained by both analytical techniques do not differ significantly (p > 0.05), confirming their feasibility for furosine analysis in soy-based products.     

Drug-plasma protein binding assay by electrokinetic chromatography-frontal analysis

We developed a rapid, microscale and reliable analytical method for binding of drugs to plasma proteins using capillary electrophoresis (CE) with ionic cyclodextrins (CD) combined with frontal analysis. These CDs were used as pseudostationary phases of electrokinetic chromatography (EKC). The CD-modified EKC (CDEKC) approach allowed us to separate anionic drugs from plasma proteins, whereas CZE could not separate these drugs from plasma proteins because they had a similar mobility like plasma proteins. CDs uniquely interact with these drugs but not with plasma proteins. Therefore, CDEKC could be coupled with frontal analysis to measure the binding of anionic drugs to plasma proteins. The binding values obtained by CDEKC were highly consistent with those determined by the ultrafiltration method. Our CDEKC approach should expand the applicability of CE to protein binding analysis.     

Determination and regulation of the migration window in electrokinetic chromatography

The determination of the velocities of the mobile and the pseudostationary phases (the migration (time) window) is mandatory for the determination of physicochemical properties by electrokinetic chromatography (EKC). This review offers a detailed discussion on the definition, the importance, the determination and the regulation of the migration (time) window in EKC. An overview on the theoretical treatment of chromatographic processes in EKC is given defining EKC in comparison to the term capillary electrophoresis. Methods to determine and influence the migration window are discussed with emphasis on measures that have been taken to modify the electroosmotic flow velocity. Pseudostationary phases (or separation carriers) that are taken into consideration are anionic and cationic micelles, mixed micelles, microdroplets (microemulsions), polymeric pseudostationary phases and dendrimers.     

Analysis of ion-association reaction in aqueous solution and its utilization by capillary zone electrophoresis.

Electrophoretic migration of analytes in capillary zone electrophoresis (CZE) reflects the dissolved status of analytes in solution, and the electrophoretic mobility is controlled to develop the resolution among analytes by adding a "modifier" to the migrating solution. Such addition of modifier is essentially the utilization of molecular interactions. Precise measurement of electrophoretic mobility by CZE allows analyzing molecular interactions, and CZE apparatus is very useful for physicochemical measurements. This review focuses on the advantages on using CZE to analyze equilibrium reaction; the capillary electrophoretic method and mathematical analyses that apply acid dissociation and complex formation reactions are also validated. Ion association reactions are deeply related to analytical chemistry and separation science, and CZE has been used for the investigation of ion-ion interactions. Various types of interactions have been clarified through the CZE measurements: contributions of hydrophobicity, probability, and aromatic-aromatic interaction were quantitatively evaluated. Ion association reaction in aqueous solution also elucidates the stepwise reactions of liquid-liquid distribution of ion associates. Development and applications of ion association reaction in CZE analysis are also introduced.     

Potential use of capillary zone electrophoresis in size characterization of quantum dots for environmental studies

Quantum dot (QD) nanoparticles (NPs) are of great interest to various researchers due to their wide range of applications, from photovoltaic sensitizers to in vivo fluorescent probes. There is a need to characterize environmental fate, degradation, and ecotoxicity of QDs because these NPs may be introduced into the environment upon disposal of waste products containing QDs following the anticipated increase in their production and use. Because the properties of QDs are defined primarily by their composition and size, it is imperative that QD size be measured accurately and quickly. Current methods for measuring the size of QDs tend to be relatively slow, require large amounts of sample and may not be suitable for environmental or biological samples. Capillary zone electrophoresis (CZE), with its inherently high separation efficiency based on the size-to-charge ratio of analytes, holds promise for efficient size determination of NPs in aqueous samples.This review examines the potential use of CZE in characterizing and separating QDs compared to the conventional methods employed in determining size distribution of NPs. We briefly discuss the advantages and the limitations of commonly used techniques for size characterization.In addition to published literature, we present results from our laboratory using CZE with laser-induced fluorescence (LIF) to examine the effect of natural organic matter and buffer composition on the electrophoretic mobility of QDs. The use of CZE in environmental studies can provide insights into the degradation and the potential impacts of QDs upon exposure to environmental and biological matrices.     

Metabolic fingerprinting of Schistosoma mansoni infection in mice urine with capillary electrophoresis

Schistosoma mansoni infection in mice has been fingerprinted using CE to study the capabilities of this technique as a diagnostic tool for this parasitic disease. Two modes of separation were used in generating the electrophoretic data, with each untreated urine sample the following methods were applied: (i) a fused-silica capillary, operating with an applied potential of 18 kV, in micellar EKC (MEKC) and (ii) a polyacrylamide-coated capillary, operating with an applied potential of -20 kV under zonal CZE conditions. By combining normal and reverse polarities in the data treatment we have extracted more information from the samples, which is a better approach for CE metabolomics. The traditional problems associated with variability in electrophoretic peak migration times for analytes were countered by using a dynamic programming algorithm for the electropherograms alignment. Principal component analyses of these aligned electropherograms and partial least square discriminant analysis (PLS-DA) data are shown to provide a valuable means of rapid and sample classification. This approach may become an important tool for the identification of biomarkers, diagnosis and disease surveillance.     

Determination of (E)-10-hydroxy-2-decenoic acid content in pure royal jelly: a comparison between a new CZE method and HPLC

A new CZE method was developed and compared with HPLC for the determination of (E)-10-hydroxy-2-decenoic acid (10-HDA) in royal jelly (RJ) samples of different geographical origin. The results obtained with the CZE method were highly correlated with those of HPLC (p < 0.01). Under optimized conditions, CZE employed minimal amounts of 50 mM tetraborate buffer as BGE, without the addition of organic solvents, EOF or pH modifiers. The CZE method showed a wide linear response range (0.006-0.808 mg 10-HDA/mL), a good sensitivity (LOD and LOQ were 0.002 and 0.004 mg/mL, respectively) and a satisfactory instrumental repeatability with respect to migration time and peak area (RSD% less than 1.0 and 2.0% on migration time for intra- and interday assay, respectively and less than 2.0 and for 4.0% on peak area for intra- and interday assay, respectively). The 10-HDA content in RJ ranged from 0.8 to 3.2 g/100 g of RJ and a significant difference (p < 0.05) was found between the Italian and extra-European average values: 2.5 and 1.6 g/100 g of RJ, respectively, according to the CZE data. The possibility of application of CZE for routine analyses on RJ and RJ based products to verify their authenticity is highlighted here.     

Capillary zone electrophoresis and capillary electrophoresis-mass spectrometry for analyzing qualitative and quantitative variations in therapeutic albumin

The present study describes a reproducible and quantitative capillary zone electrophoresis (CZE) method, which leads to the separation of nine forms (native, oxidized and glycated) of human serum albumin (HSA). In an attempt to identify the different species separated by this CZE method, the capillary electrophoresis was coupled to mass spectrometry using a sheath liquid interface, an optimized capillary coating and a suitable CE running buffer. CE-MS analyses confirmed the heterogeneity of albumin preparation and revealed new truncated and modified forms such as Advanced Glycation End products (AGEs). Assignment of the CZE peaks was carried out using specific antibodies, carboxypeptidase A or sample reduction before or during the CE separation. Thus, five HSA forms were unambiguously identified. Using this CZE method several albumin batches produced by slightly different fractionation ways could be discriminated. Furthermore, analyses of HSA preparations marketed by five pharmaceutical industries revealed that two therapeutic albumins, including that marketed by LFB, contained the highest proportion of native form and lower levels of oxidized forms.     

Capillary electrophoresis of natural products-II

Capillary zone electrophoresis (CZE) and micellar electrokinetic capillary chromatography (MEKC) were used for the separation of widely different compounds from natural materials including compounds from tea, acids from different matrices, flavonoids and alkaloids, toxins and toxicological compounds, proteins and polypeptides, biogenic amines, phenolic compounds in alcoholic beverages, Chinese medicinal drugs, compounds in cells and cell extracts, and miscellaneous other applications. A section dealing with recent reviews related to natural products is also included.     

Generalized model of the linear theory of electromigration and its application to electrokinetic chromatography: Theory and software PeakMaster 6—Next Generation

The linear theory of electromigration, including the first‐order nonlinear approximation, is generalized to systems with any equilibria fast enough to be considered instantaneous in comparison with the timescale of peak movement. For example, this theory is practically applied in the electrokinetic chromatography (EKC) mode of the CZE. The model enables the calculation of positions and shapes of analyte and system peaks without restricting the number of selectors, the complexation stoichiometry, or simultaneous acid–base equilibria. The latest version of our PeakMaster software, PeakMaster 6—Next Generation, implements the theory in a user‐friendly way. It is a free and open‐source software that performs all calculations and shows the properties of the background electrolyte and the expected electropherogram within a few seconds. In this paper, we mathematically derive the model, discuss its applicability to EKC systems, and introduce the PeakMaster 6 software.     

CEC and EKC of natural compounds

In this review, an overview of CEC and EKC methods with their developments are summarized for different natural compounds. It is divided into three main parts. The first part elaborates the separation of lipophilic compounds without any charged groups. The second part constitutes CEC and EKC of lipophilic compounds containing ionizable functional groups whereas the third part contains hydrophilic compounds. Packed, monolithic, coated, or raw fused-silica (FS) capillaries are among the choice for stationary phases. Applications of these phases on the above-mentioned three classes of compounds, coupled with different detection methods, e.g. MS or LIF, are explored and their advantages and disadvantages are discussed.     

毛细管区带电泳监测牛胰岛素的去折叠过程

用毛细管区带电泳监测了二硫苏糖醇作用下二硫键还原引起的牛胰岛素去折叠全过程,同时用离线的基质辅助激光解吸／电离飞行时间的质谱配合确证。从毛细管电泳谱图能直接观察胰岛素去折叠过程中发生的变化,获得蛋白质去折叠信息。结果表明,毛细管区带电泳作为监测蛋白质构象变化的一种有效手段,方法简便、快速、灵敏度高、样品消耗量少。