The use of capillary electrophoresis in a micropreparative mode: methods and applications

Capillary electrophoresis of DNA in uncrosslinked polymer solutions: evidence for a new mechanism of DNA separation

The electrophoretic separation of DNA molecules is usually performed in thin slabs of agarose or polyacrylamide gel. However, DNA separations can be achieved more rapidly and efficiently within a microbore fused silica capillary filled with an uncrosslinked polymer solution. An early assumption was that the mechanism of DNA separation in polymer solution-capillary electrophoresis (PS-CE) is the same as that postulated to occur in slab gel electrophoresis, i.e., that entangled polymer chains form a network of "pores" through which the DNA migrates. However, we have demonstrated that large DNA restriction fragments (2.0-23.1 kbp) can be separated by CE in extremely dilute polymer solutions, which contain as little as 6 parts per million [0.0006% (w/w)] of uncrosslinked hydroxyethyl cellulose (HEC) polymers. In such extremely dilute HEC solutions, far below the measured polymer entanglement threshold concentration, pore-based models of DNA electrophoresis do not apply. We propose a transient entanglement coupling mechanism for the electrophoretic separation of DNA in uncrosslinked polymer solutions, which is based on physical polymer/DNA interactions.

Ionization techniques in capillary electrophoresis-mass spectrometry: principles, design, and application

A major step forward in the development and application of capillary electrophoresis (CE) was its coupling to ESI-MS, first reported in 1987. More than two decades later, ESI has remained the principal ionization technique in CE-MS, but a number of other ionization techniques have also been implemented. In this review the state-of-the-art in the employment of soft ionization techniques for CE-MS is presented. First the fundamentals and general challenges of hyphenating conventional CE and microchip electrophoresis with MS are outlined. After elaborating on the characteristics and role of ESI, emphasis is put on alternative ionization techniques including sonic spray ionization (SSI), thermospray ionization (TSI), atmospheric pressure chemical ionization (APCI), atmospheric pressure photoionization (APPI), matrix-assisted laser desorption ionization (MALDI) and continuous-flow fast atom bombardment (CF-FAB). The principle of each ionization technique is outlined and the experimental set-ups of the CE-MS couplings are described. The strengths and limitations of each ionization technique with respect to CE-MS are discussed and the applicability of the various systems is illustrated by a number of typical examples.

From micro to macro: conversion of capillary electrophoretic separations of biomolecules and bioparticles to preparative free-flow electrophoresis scale

This invited contribution in the special issue of Electrophoresis published in celebration of the 30th Anniversary of this journal reflects the impact of our milestone paper [Prusík, Z., Kasicka, V., Mudra, P., Stepánek, J., Smékal, O., Hlavácek, J., Electrophoresis 1990, 11, 932-936] in the area of conversion of microscale analytical and micropreparative CE separations of biomolecules and bioparticles into (macro)preparative free-flow electrophoresis (FFE) scale on the basis of a correlation between CE and FFE methods. In addition to the survey of advances in the relatively narrow field of CE-FFE correlation and CE-FFE conversion, a comprehensive review of the recent developments of micropreparative CE and (macro)preparative FFE techniques is also presented and applications of these techniques to micro- and (macro)preparative separations and purifications of biomolecules and bioparticles are demonstrated. The review covers the period since the year of publication of the above paper, i.e. ca. the last 20 years.

Identification of a specific marker for hepatitis C virus infection using capillary zone electrophoresis

BACKGROUND

Hepatitis C virus (HCV) infection is now becoming a common health problem in both developed and developing countries. The limitation of the available diagnostic approaches enhances the efforts to have a rapid, sensitive, and specific diagnostic testing for HCV infection. Capillary zone electrophoresis (CZE) is a fully automated analytical technique whose popularity is quickly increasing in the clinical chemistry laboratory. CZE can analyze nanoliters or less of samples with detection sensitivity at the attomole level (10(-18) mol) or less.

METHODS

CZE was optimized for the identification of a specific marker of HCV infection. The performance characteristics of the CZE for the detection of HCV RNA peak were evaluated in comparison with standard nested PCR.

RESULTS

A characteristic peak at 2.72 min was identified only in the CZE electropherogram of urine samples from HCV-infected individuals. The nature of the characteristic peak was investigated and confirmed to be HCV RNA using PCR and other biochemical treatments including RNase, DNase, and trypsin enzymes. CZE showed high degrees of sensitivity (94%) and specificity (96%) in comparison with the nested PCR.

CONCLUSION

CZE provides a rapid, inexpensive, sensitive, and specific analytical method for diagnosis and mass screening of a large number of HCV-infected individuals.

Fraction collection in micropreparative capillary zone electrophoresis and capillary isoelectric focusing

A new fraction collection system for capillary zone electrophoresis (CZE) and capillary isolelectric focusing (CIEF) is described. Exact timing of the collector steps was based on determining the velocity of each individual zone measured between two detection points close to the end of the capillary. Determination of the zone velocity shortly before collection overcame the need for constant analyte velocity throughout the column. Consequently, sample stacking in CZE with large injection volumes as well as zone focusing in CIEF could be utilized with high collection accuracy. Capillaries of 200 microm inner diameter (ID) were employed in CZE and 100 microm ID in CIEF for the micropreparative mode. A sheath flow fraction collector was used to maintain permanent electric current during the collection. The bulk liquid flow due to siphoning, as well as the backflow arising from the sheath flow droplet pressure, were suppressed by closing the separation system at the inlet with a semipermeable membrane. In the CZE mode, the performance of the fraction collector is demonstrated by isolation of individual peaks from a fluorescently derivatized oligosaccharide ladder. In the CIEF mode, collection of several proteins from a mixture of standards is shown, followed by subsequent analysis of each protein fraction by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS).

Strategies for capillary electrophoresis: method development and validation for pharmaceutical and biological applications

This review is in support of the development of selective, reproducible and validated capillary electrophoretis (CE) methods. Focusing on pharmaceutical and biological applications, the successful use of CE is demonstrated by more than 800 references, mainly from 1994 until 1998. Approximately 80 recent reviews have been catalogued. These articles sum up the existing strategies for method development in CE, especially in the search for generally accepted concepts, but also looking for new, promising reagents and ideas. General strategies for method development were derived not only with regard to selectivity and efficiency, but also with regard to precision, short analysis time, limit of detection, sample pretreatment requirements and validation. Standard buffer recipes, surfactants used in micellar electrokinetic capillary chromatography (MEKC), chiral selectors, useful buffer additives, polymeric separation media, electroosmotic flow (EOF) modifiers, dynamic and permanent coatings, actions to deal with complex matrices and aspects of validation are collected in 20 tables. Detailed schemes for the development of MEKC methods and chiral separations, for optimizing separation efficiency, means of troubleshooting, and other important information for key decisions during method development are given in 19 diagrams. Method development for peptide and protein separations, possibilities to influence the EOF and how to stabilize it, as well as indirect detection are considered in special sections.

Polymeric separation media for capillary electrophoresis of nucleic acids

The choice of polymer matrix for separating nucleic acids by capillary electrophoresis has often been arbitrary. However, considerable research in the area has led to a wealth of data exploring the key parameters of the polymer matrix that affect nucleic acid separations: polymer type, polymer molecular mass, polymer concentration, temperature, and buffer components and additives. Using this information, it is possible to use rational methods of choosing a good polymer matrix for a particular application. Further research into the properties of the mechanism of separation in polymer solutions, as well as the polymer matrix and other solution components will lead to even more efficient separations.

Peptide analysis by capillary (zone) electrophoresis

In this review various aspects concerning the application of capillary (zone) electrophoresis for peptide analysis will be critically examined. First, the basic instrumental requirements of CE apparatus and the strategies employed to enhance sensitivity in the analysis of underivatized sample are described. Multidimensional separative techniques of complex peptide mixtures that use CE as final step and the coupling of CE with mass spectrometry are subsequently discussed. A theoretical section describes the relationships existing between peptide mobility and the pH of the separation buffer. These relationships evidence that proton dissociation constants and Stokes radius at different protonation stages can be calculated by measuring the electrophoretic mobility at different pH values. Investigation of peptide mobility dependence on pH allows us to establish the optimum conditions, in terms of resolution, for peptide separation. Subsequently, a critical discussion about semiempirical models predicting peptide mobility as a function of chemico-physical peptide properties is presented. A section is devoted to the description of principles of peptide affinity capillary electrophoresis, underlining the similarity with peptide-proton interaction. CE separations performed in aquo-organic solvents are also critically discussed, showing the good performance obtained by using water-2,2,2-trifluoroethanol solutions. Finally, selected CE applications for the determination of peptide chemico-physical properties and conventional analysis, like peptide mapping, are reported.

Micropreparative capillary electrophoresis of DNA by direct transfer onto a membrane

We have developed a new technique for the collection of DNA fragments separated by capillary electrophoresis, by direct transfer from the capillary outlet to a positively charged membrane. Transfer and post-run detection of two different nonradioactively labeled DNA standards, ranging in size from 150 bp to 2 kbp and 120 bp to 23 kbp are presented, and discussed. Capillary electrophoresis with direct blotting presents several advantages over the blotting from gels: the separation is faster and requires less manual steps, the resolution is higher, and each DNA fragment is collected into a very concentrated spot on the membrane due to the small surface of the capillary outlet and to a design of the collection device inducing a refocusing of field lines across the hybridization membrane. Therefore, very small amounts of DNA (in the pg range) can be detected. This fraction collection makes further analysis of the sample possible, e.g. by hybridization, thus suppressing one of the major present limitations of the capillary electrophoresis technique for DNA analysis.

Capillary electrophoresis of recombinant proteins

Many naturally occurring proteins which are used therapeutically have been cloned and expressed in large quantities in bacterial, yeast or mammalian systems. Purification of these proteins by column chromatography generates high purity products with low levels of host protein contaminants. However, isoforms of the desired protein may be present at variable concentrations. Analysis of these variant forms has been enhanced by the utilisation of capillary electrophoresis (CE), a highly efficient, widely applicable technique which is increasingly used in the field of biotechnology. The role of CE in the analysis of recombinant proteins is reviewed with respect to microcharacterisation, comparison of natural and recombinant proteins, separation of mutant or variant forms and analysis of glycoforms. Examples of these applications are described and illustrated with analysis of recombinant human albumin. The rapid development of CE, further enhancing its versatility, and its use with complementary analytical techniques is also discussed.

Combination of micropreparative capillary electrophoresis and matrix-assisted laser desorption/ionization mass spectrometry for peptide analysis

Signal suppression is a problem in matrix-assisted laser desorption/ionization mass spectrometry of peptides prepared by capillary electrophoresis. Many common electrolytes that are efficient for separation, such as sodium phosphate, also are strongly suppressive during laser desorption/ionization. We have tested individual electrolytes for highest performance in each step of separation and collection, respectively. Suppression is not observed if citrate, trifluoroacetic acid, or hydrochloric acid is used for collection, while phosphate still can be employed in the capillary providing excellent resolution. Low concentrations of hydrochloric acid added to the sample/matrix mixture generate mass spectra with better ion intensities than if trifluoroacetic acid or citrate is used.

Micropreparation of peptides by capillary electrophoresis for matrix assisted laser desorption mass spectrometry

In the separation of peptides by capillary electrophoresis and analysis by matrix assisted laser desorption mass spectrometry, strong suppression of the mass spectrometric signals is a problem with many common electrolytes used in the separation step such as sodium phosphate. We describe an approach employing individual electrolytes selected for highest performance in each process. Suppression with samples collected into phosphate buffers is avoided when citrate, trifluoroacetic acid or hydrochloric acid is used for collection, while phosphate still provides excellent resolution in the capillary. Low concentrations of hydrochloric acid added to the sample/matrix mixture generate essentially adduct-free mass spectra with better signal-to-noise ratios and detection limits (fmol range) than those obtained with citrate or trifluoroacetic acid. Addition of 0.25% ethylene glycol to both the phosphate electrolyte and the sample improves peak shape and resolution, and is crucial for preparative separations in large diameter capillaries.

Separation of negatively charged carbohydrates by capillary electrophoresis

Capillary electrophoresis (CE) has recently emerged as a highly promising technique consuming an extremely small amount of sample and capable of the rapid, high-resolution separation, characterization, and quantitation of analytes. CE has been used for the separation of biopolymers, including acidic carbohydrates. Since CE is basically an analytical method for ions, acidic carbohydrates that give anions in weakly acid, neutral, or alkaline media are often the direct objects of this method. The scope of this review is limited to the use of CE for the analysis of carbohydrates containing carboxylate, sulfate, and phosphate groups as well as neutral carbohydrates that have been derivatized to incorporate strongly acidic functionality, such as sulfonate groups.

High-performance capillary electrophoretic separation of proteins and peptides using a bonded hydrophilic phase capillary

High performance capillary electrophoresis (HPCE) was applied to the separation of protein and peptide mixtures with molecular masses ranging from 1300 to 96000 Da using a new bonded hydrophilic phase capillary, CElect-P150. This coated capillary reduces the interaction between proteins and silanol groups in capillary walls, allowing a complete recovery of the proteins and peptides of interest. HPCE was also used for the analysis of a complex mixture of tryptic fragments and to monitor the process of enzymatic digestion. Moreover, using a CElect-P150 capillary, highly reproducible analysis was possible without preconditioning the capillary with acid or basic solutions before each new analysis.

Preparative capillary zone electrophoresis of synthetic peptides conversion of an autosampler into a fraction collector

Preparative capillary zone electrophoresis of three synthetic peptides was performed either manually or automatically by simple manipulations of a commercial electropherograph that is equipped only with an autosampler without any built-in fraction collection capability. Manual fraction collection was achieved by replacing the outlet (cathode) beaker with a microcentrifuge tube, and automatic fraction collection was accomplished by converting the electropherograph's autosampler into a fraction collector. The latter was easily achieved mainly by the use of an extension wire, which completed the electrical circuit and facilitated fraction collection either at a specified time or within fixed time intervals.

Use of capillary electrophoresis-electrospray ionization mass spectrometry in the analysis of synthetic peptides

We have constructed a capillary electrophoresis (CE) system with UV detection and have successfully interfaced it to an electrospray ionization mass spectrometry (ES-MS) system. A synthesized fragment of heregulin-beta (212-226) was thought to be a single component by re-injection into an HPLC system, but results from CE-UV-ES-MS indicated that a dehydration product was present in the desired peptide sample. A synthetic heregulin-alpha (177-241) was isolated by preparative HPLC, but re-injection on an analytical system indicated a tailing peak. CE-UV-ES-MS indicated a mixture whose two major components were of the same nominal molecular mass (within experimental error), suggesting the presence of an isomer or a deamidation product. The results show that CE-UV-ES-MS can be used as an orthogonal analytical technique to solve practical problems encountered in peptide synthesis laboratories.

A transient entanglement coupling mechanism for DNA separation by capillary electrophoresis in ultradilute polymer solutions

Using capillary electrophoresis, large DNA molecules (2.0-23.1 kbp) may be rapidly separated in ultradilute polymer solutions (< 0.002% w/w) under a high-voltage, steady field (265 V/cm). At this polymer concentration, the separation mechanism appears to be significantly different from that postulated to occur in crosslinked gels. Based on experimental results obtained with DNA restriction fragments and with negatively charged latex microspheres, we conclude that the Ogston and reptation models typically used to describe gel electrophoresis are not appropriate for DNA separations in such dilute polymer solutions. Electrophoresis experiments employing solutions of both small and large hydroxyethyl cellulose polymers highlight the importance of polymer length and concentration for the optimum resolution of DNA fragments varying in size from 72 bp to 23.1 kbp. A transient entanglement coupling mechanism for DNA separation in dilute polymer solutions is developed, which suggests that there is no a priori upper size limit to DNA that can be separated by capillary electrophoresis in a constant field.

Protein electrophoresis

Many significant advances have occurred recently in the field of protein electrophoresis and related technologies. Improvements have been made in capillary electrophoresis in apparatus design, detection, and capillary modification with coatings and fillers. The transfer of proteins to a blot, the capacity to analyze and detect proteins on it, and the ability to remove proteins from a blot, are also areas where important work has been done. Finally, gel electrophoresis has benefitted from new hardware, detergent and stain protocols, and matrices.