Preparation of an iminodiacetic acid-modified capillary and its performance in capillary liquid chromatography and immobilized metal chelate affinity capillary electrophoresis

We prepared iminodiacetic acid (IDA)-modified and Cu(II)-IDA-modified capillaries through polymerization of N-(vinylbenzylimino) diacetic acid. The fundamental performance of these capillaries was examined in capillary liquid chromatography (LC) and immobilized metal chelate affinity capillary electrophoresis (IMACE). Copper(II), cobalt(II), and hematin were detected at different retention times by means of capillary LC with a chemiluminescence detector, during which the IDA-modified capillary was used. The difference in the retention times was attributed to the difference in the interaction between metal ions or complex and IDA moieties on the inner wall of the capillary. In addition, human serum albumin (HSA) and human serum gamma-globulin (HgammaG) were separated and detected using IMACE with an absorption detector, during which the Cu(II)-IDA-modified capillary was used. The separation of HSA and HgammaG was achieved through the interaction between proteins and Cu(II) chelate moieties on the inner wall of this capillary.     

Whole-column imaging capillary electrophoresis of proteins with a short capillary

Whole-column imaging capillary electrophoresis with a short capillary is discussed. A short capillary (3-6 cm) coated with either fluorocarbon or polyacrylamide was used as a separation capillary. The whole capillary was illuminated with 280 nm light, and the transmitted light was monitored by a linear charge-coupled device (CCD). For the short capillary, hydrodynamic flow caused by a subtle height difference between the anodic and cathodic reservoirs affected the sample migration in the capillary greatly. Several sample injection methods, including use of a cross connection, sealing of the capillary ends with a gel, and use of a gel-filled capillary, have been discussed. The experimental results showed that the peak height decreased and peak width increased with the electromigration distance. Therefore, higher sensitivity was obtained in a short capillary rather than a long capillary. The whole-column imaging CE with the short capillary has been applied for the study of conjugation reactions of protein cytochrome c with sodium dodecyl sulfate (SDS) and the dye Congo Red. The method has also been used for in situ monitoring of the electrophoretic protein desorption process. Our technique is a unique tool for the study of protein binding reactions and the interaction between analyte and inner wall of the capillary.     

Polymeric ionic liquid-coated capillary for capillary electrophoresis

A new application of the polymeric ionic liquid (PIL) in capillary electrophoresis is reported. Poly(1-vinyl-3-butylimidazolium bromide) was physically adsorbed on silica capillary as the simple and effective coating for capillary electrophoresis (CE) analysis, in which the PIL is not present in the background electrolyte. The electroosmotic flow (EOF) of the PIL-coated capillary as compared with that of the bare fused-silica capillary shows a different dependence on electrolyte pH values. The EOF is reversed over a wide pH range from 3.0 to 9.0 and shows good repeatability. It is also found that the coated capillary has a good tolerance to some organic solvents, 0.1 M NaOH and 0.1 M HCl. The PIL-coated capillary has been employed in different areas. Both the basic proteins and anionic analytes can be well separated by PIL-coated capillaries in a fast and easy way. The PIL-coated capillary is also able to separate organic acid additives in a grape juice. The results showed that this type of coating provides an alternative to the CE separation of anions and basic proteins.     

Splitless on-line coupling of capillary high-performance liquid chromatography,capillary electrochromatography and pressurized capillary electrochromatography with nuclear magnetic resonance spectroscopy

A mixture of unsaturated fatty acid methyl esters was separated with a new splitless capillary set-up. With the employed apparatus configuration different capillary separation techniques such as capillary high-performance liquid chromatography (cHPLC), capillary electrochromatography (CEC) and pressurized capillary electrochromatography (pCEC) could be applied. The detection and identification of the sample compounds were accomplished by hyphenating these capillary separation techniques with nuclear magnetic resonance (NMR) spectroscopy using a novel configuration of the detection capillary set-up. Using modified electrokinetically driven separation techniques, the electric field was applied solely across the separation column. With this improved interface for capillary liquid chromatography-NMR on-line coupling, the stereochemical assignment of the cis and trans configuration of unsaturated fatty acids could be easily accomplished. Finally, the results of cHPLC-NMR, CEC-NMR and pCEC-NMR coupling experiments were compared.Dedicated to Professor Günter Häfelinger on the occasion of his 65th birthday     

Joule heating and determination of temperature in capillary electrophoresis and capillary electrochromatography columns

This article reviews the progress that has taken place in the past decade on the topic of estimation of Joule heating and temperature inside an open or packed capillary in electro-driven separation techniques of capillary electrophoresis (CE) and capillary electrochromatography (CEC), respectively. Developments in theoretical modeling of the heat transfer in the capillary systems have focused on attempts to apply the existing models on newer techniques such as CEC and chip-based CE. However, the advent of novel analytical tools such as pulsed magnetic field gradient nuclear magnetic resonance (NMR), NMR thermometry, and Raman spectroscopy, have led to a revolution in the area of experimental estimation of Joule heating and temperature inside the capillary via the various noninvasive techniques. This review attempts to capture the major findings that have been reported in the past decade.     

Titanium dioxide coated surfaces for capillary electrophoresis and capillary electrochromatography

The potential of titanium dioxide coatings to control the electroosmotic flow and to affect the migration behavior of analytes in capillary electrophoresis and open-tubular capillary electrochromatography was evaluated. The inner wall of a fused-silica capillary was applied with a solution of a titanium peroxo complex, followed by heating at an elevated temperature. The resultant product was ascertained to be titanium dioxide in a crystalline form of anatase by the results of Fourier transform-infrared spectrometry (FT-IR), X-ray photoelectron spectroscopy, and Raman spectroscopy. The capillary thus made had anodic or cathodic electroosmotic flow, depending on the pH and composition of the background electrolyte used. The titanium dioxide surface of the capillary was readily modified by a silanizing reagent. The performance of the titanium dioxide surfaces with or without chemical modifications was examined with inorganic anions, neutral compounds and peptides.     

Recent advances in capillary electrophoresis and capillary electrochromatography of pollutants

Recent advances in capillary electrophoresis (CE) and capillary electrochromatography (CEC) separation, detection and sample preparation methodologies applied for the determination of a variety of pollutants is overviewed. The reviewed literature illustrates the wide range of CE applications, indicating the continuing interest in CE and CEC in the environmental field.     

Preparation of a sulfonated fused-silica capillary and its application in capillary electrophoresis and electrochromatography

In the present paper, two new methods, sol-gel and chemical bonding methods, were proposed for preparation of sulfonated fused-silica capillaries. In the sol-gel method, a fused-silica capillary was coated with the sol solution obtained by hydrolysis of 3-mercaptopropyltrimethoxysilane (MPTS) and tetramethoxysilane, and followed by age; while in the chemical bonding method, a capillary was chemically bonded directly with MPTS. Then, both the resulting capillaries were oxidized with an aqueous solution of hydrogen peroxide solution (H2O2) (30%, m/m) to obtain the sulfonated capillaries. The electroosmotic flow (EOF) for the sulfonated capillaries was found to remain almost constant within the studied pH range, and greater than that of the uncoated capillary. However, the coating efficiency of the capillary prepared by chemical bonding method was higher than that by sol-gel method, by comparing their magnitude of the EOF, the degree of disguise of the silanol and reproducibility of preparation procedure. The effects of the electrolyte's concentration and the content of methanol (MeOH) on the EOF were also studied. Especially, the study of the apparent pH (pH*) on the EOF in a water-MeOH system was reported. Finally, capillary electrophoretic separation of seven organic acids was achieved within 6.5 min under optimal condition using the chemically bonded sulfonated capillary. Moreover, separation of four alkaloids on the sulfonated capillary was compared with that on uncoated capillary in different conditions. Ion-exchange mechanism was found to play a key role for separation of these four basic analytes on the sulfonated capillary.     

Analytical potential of enzyme-coated capillary reactors in capillary zone electrophoresis

Enzymes immobilized on the inner surface of an electrophoretic capillary were used to increase sensitivity and resolution in capillary zone electrophoresis (CZE). Sensitivity is enhanced by inserting a piece of capillary containing the immobilized enzyme into the main capillary, located before the detector, in order to transform the analyte into a product with a higher absorptivity. This approach was used to determine ethanol. In order to improve resolution, capillary pieces containing immobilized enzymes were inserted at various strategic positions along the electrophoretic capillary. On reaching the enzyme, the analyte was converted into a product with a high electrophoretic mobility, the migration time for which was a function of the position of the enzyme reactor. This approach was applied to the separation and determination of acetaldehyde and pyruvate. Finally, the proposed method was validated with the determination of ethanol, acetaldehyde, and pyruvate in beer and wine samples.     

Interaction between netropsin and double-stranded DNA in capillary zone electrophoresis and affinity capillary electrophoresis

Poor sensitivity and low phase ratio are the main drawbacks of open tubular capillary electrochromatography (OTCEC). The poor sensitivity results from the use of narrow bore size capillary, whereas the low phase ratio, which limits the separation capability, is caused by the limited surface area of conventional capillary. Two strategies may be useful to overcome these disadvantages. First, an extended light path (ELP) capillary, which has a bubble cell at the detection point, is used to improve the sensitivity. Secondly, an etched capillary of a 1,000-fold increased surface area is used to enhance the phase ratio. In this work, use of an ELP capillary and an etched capillary in OTCEC was evaluated with a chiral stationary phase of avidin prepared with the physical adsorption method. With a 20 microm I.D. ELP capillary with a 150 microm bubble cell, the peak height was enhanced by 4-10-fold and the corrected peak area was increased by 12-fold relative to a 20 microm I.D. conventional capillary. However, the peak efficiency and resolution decreased noticeably. The phase ratio on the etched capillary was slightly enhanced, by a factor of 1.64 relative to an unetched capillary. Consequently, the separation capability was slightly improved. The increase in the phase ratio was much lower than that expected from the increase in surface area, the reason for which is probably the reduced density of surface silanol group and the generation of nitrogen-containing groups due to the etching process.     

Nonaqueous capillary electrophoresis using a titania-coated capillary

In this work, an ordered mesoporous titania film was introduced to coat a capillary by means of the sol-gel technique. Its electroosmotic flow (EOF) property was investigated in a variety of nonaqueous media (methanol, formamide and N,N'-dimethylformamide and mixtures of methanol and acetonitrile). The titania-coated capillary exhibited a distinctive EOF behavior, the direction and magnitude of which were strongly dependent on various parameters such as the solvent composition, apparent pH (pH*) and the electrolytes. The nonaqueous capillary electrophoresis separation of several alkaloids was investigated in the positively charged titania-coated capillary. Comparison of separation between coated and uncoated capillaries under optimal nonaqueous conditions was also carried out.     

Study of triacontyl-functionalized monolithic silica capillary column for reversed-phase capillary liquid chromatography

A novel stationary phase triacontyl-functionalized monolithic silica capillary column was successfully prepared for reversed-phase capillary liquid chromatography. The performance of the monolithic silica capillary column coated with triacontyl chain for the separation of alkylbenzenes, xylene isomers, polycyclic aromatic hydrocarbons, and mixture of α- and β-carotenes was studied, which was compared to that using the monolithic silica capillary column coated with octadecyl chain. The comparison results showed that triacontyl-functionalized monolithic silica capillary column would be a promising media to be used for the separation of isomeric solutes with long chain in reversed-phase capillary liquid chromatography.     

Miniaturization of capillary electrochromatography using an ultrashort capillary column

The instrumentation for miniaturization of capillary electrochromatography was devised and an injection method for this apparatus was proposed. By using an ultra short capillary column (15 mm packed length, 36 mm total length, 75 microm inner diameter, packed with cation exchange supports), the separation of five biochemical compounds was performed within 1 min. The high separation efficiency of 9780 plates was achieved by using an ultrashort capillary column. The miniaturized instrumentation for capillary electrochromatography might be utilized as one of the possible methods in microfabricated analysis or in an alternative approach to it.     

Stationary phases for capillary electrophoresis and capillary electrochromatography

An overview of the most recent developments in column technology employed in capillary electrophoresis (CE) and capillary electrochromatography (CEC), mainly for the separation of small molecules and ions, is presented. Particular emphasis is laid on permanent coating. The wall modification methods in CE include covalent modification, adsorbed coatings and polymeric coatings, while those in CEC include packed columns, open-tubular columns and fritless columns. A short discussion on the characterization and selectivity of the bonded phases is also given.     

Recent advances in capillary electrophoresis and capillary electrochromatography of pollutants

An overview of major developments in capillary electrophoresis and capillary electrochromatography systems in the environmental field is presented, covering relevant publications between the second half of 1999 and early 2001. Contributions are reviewed in relation to developments in detection, sample preparation/preconcentration, precision and applications. Many interesting examples are shown and the influence of important parameters on the performance of developed methods is discussed.     

Overview of capillary electrophoresis and capillary electrochromatography.

This paper provides an overview on the current status of capillary electrophoresis (CE) and capillary electrochromatography (CEC). The focus is largely on the current application areas of CE where routine methods are now in place. These application areas include the analysis of DNA, clinical and forensic samples, carbohydrates, inorganic anions and metal ions, pharmaceuticals, enantiomeric species and proteins and peptides. More specific areas such the determination of physical properties, microchip CE and instrumentation developments are also covered. The application, advantages and limitations of CEC are covered. Recent review articles and textbooks are frequently cited to provide readers with a source of information regarding pioneering work and theoretical treatments.     

A covalent capillary coating of diazoresin and polyglycerol dendrimer for protein analysis using capillary electrophoresis

Overcoming proteins adsorption on the inner surface of capillary has attracted increasing attention recently. By using the unique photochemistry reaction of diazoresin (DR), a new covalent capillary coating was prepared on the fused‐silica capillary through layer‐by‐layer self‐assembly of DR with polyglycerol (PG) dendrimer. The separation performance of covalently DR/PG‐dendrimer coated capillary noticeably exceeded the bare capillary and the noncovalently linked DR/PG‐dendrimer capillary. A baseline separation of lysozyme, myoglobin, bovine serum albumin, and ribonuclease A was achieved using CE within 20 min. Besides, the covalently linked DR/PG‐dendrimer coating has the remarkable stability and reproducibility. Especially, compared with the traditional method which use highly toxic and moisture‐sensitive silane coupling agent, this method seems to be a simple and environmental friendly way to prepare the covalently coated capillaries for CE.     

A sulfonated capillary that gives reproducible migration times for capillary zone electrophoresis and micellar electrokinetic chromatography

To obtain reproducible migration times and rapid analyses of analytes, sulfonate groups were chemically introduced to the inner wall of untreated fused-silica capillary with 2-(4-chlorosulfonylphenyl)ethyltrichlorosilane. The sulfonated capillary showed relatively constant electroosmotic mobility which was greater than that obtained by an untreated fused-silica capillary over the pH range studied (pH 2-9). In both CZE and MEKC, the RSDs of the migration times of analytes with the sulfonated capillary were less than 0.2% which were significantly lower than those obtained with an untreated fused-silica capillary (0.5-3.5%). When BGE were set at pH 7.0 for CZE and MEKC, the analysis times with the sulfonated capillary were about half those obtained with an untreated fused-silica capillary. These results indicate that the sulfonated capillary can provide highly reproducible and rapid analyses in CE.