Use of full-column imaging capillary isoelectric focusing for the rapid determination of the operating conditions in the preparative-scale continuous free-flow isoelectric focusing separation of enantiomers

Separation of tetrahydrozoline enantiomers in capillary electrophoresis with cyclodextrin-type chiral selectors and investigation of chiral recognition mechanisms

The recognition power and affinity pattern of various cyclodextrins (CD) towards the enantiomers of tetrahydrozoline (THZ) were studied using capillary electrophoresis (CE). As expected, affinity of THZ enantiomers and selectivity of recognition towards CD derivatives was strongly dependent on the cavity size and substituent type and pattern on the CD rims. Not only were the affinity strength and selectivity of recognition affected by the size of the cavity and chemistry of the CDs but also the affinity pattern. Another interesting example of opposite affinity pattern of enantiomers towards α- and β-CD was observed here. In addition, opposite affinity pattern of THZ enantiomers was seen towards β-CD and its acetylated derivatives, while methylation of β-CD did not affect the affinity pattern of THZ enantiomers. In order to get more information about structural mechanisms of the multivariate dependences mentioned above, rotating frame Overhauser enhancement spectroscopy (ROESY) and computation techniques were used. Significant differences between the structure of THZ complexes with different CDs with both methods were encountered. Good correlations between experimentally determined and computed structure of complexes, as well as between computed complex stabilities and enantiomer migration order (EMO) in CE were observed.

Current advances and challenges in microfluidic free-flow electrophoresis-A critical review

The research field on microfluidic free-flow electrophoresis has developed vast amounts of devices, methods, applications and raised new questions, often in analogy to conventional techniques from which it derives. Most efforts have been employed on device development and a myriad of architectures and fabrication techniques have been reported using simple proof-of-principle separations. As technological aspects reach a quite mature state, researchers' new challenges include the development of protocols for the separation of complex mixtures, as required in the fields of application. The success of this effort is extremely dependent on the capability to transfer the device's fabrication to an industrial setting as well as to ensure interfacing simplicity, namely at the solutions' supply and collection, and actuation such as electric potential application and temperature control. Other advanced applications such as direct interfacing to downstream systems such as mass spectrometry, integration of sensing and feedback controls will require further development in the laboratory. In this review we provide an overview on the field, from basic concepts, through advanced developments both in the theoretical and experimental arenas, and addressing the above details. A comprehensive survey of designs, materials and applications is presented with particular highlights to most recent developments, namely the integration of electrodes, flow control and hyphenation of microfluidic free-flow electrophoresis with other techniques.

Application of polymeric surfactants in chiral micellar electrokinetic chromatography (CMEKC) and CMEKC coupled to mass spectrometry

The use of amino acid-based polymeric surfactants (a.k.a. molecular micelles) in chiral micellar electrokinetic chromatography (CMEKC) has been shown to be a successful separation mode for capillary electrophoresis (CE). In this mode, chiral compounds can be enantioseparated with high efficiency, high chiral selectivity, and versatility. This chapter describes the state-of-the art studies published in the past 5 years in CMEKC using polymeric surfactants. Recent trends in the compatibility of chiral polymeric surfactants with mass spectrometric (MS) detection suggest that this type of chiral selector may be the most promising ones for chiral CE-MS applications. The synthesis of new anionic and cationic MS-compatible polymeric surfactants and their utility in CMEKC and CMEKC-MS are demonstrated. Examples of how to run a typical CMEKC-MS experiment using univariate and multivariate optimization of CMEKC and MS parameters are discussed.

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.

Side-by-side comparison of disposable microchips with commercial capillary cartridges for application in capillary isoelectric focusing with whole column imaging detection

Simple-structured, well-functioned disposable poly(dimethylsiloxane) (PDMS) microchips were developed for capillary isoelectric focusing with whole column imaging detection (CIEF-WCID). Side-by-side comparison of the developed microchips with well-established commercial capillary cartridges demonstrated that the disposable microchips have comparable performance as well as advantages such as absence of lens effect and possibility of high-aspect-ratio accompanied with a dramatic reduction in cost.

Evaluation of the iCE280 Analyzer as a potential high-throughput tool for formulation development

The iCE280 Analyzer (iCE280) was evaluated for its potential application as a high-throughput tool to determine pI and separate charge related species using glycosylated, non-glycosylated and pegylated protein therapeutics as models. Resolution was achieved for glycosylated and non-glycosylated molecules, but remained a challenge for pegylated proteins. The sources of charge variants were determined to be the presence of C-terminal lysine residues, sialic acid content, and deamidation. Limited assay performance evaluation demonstrated that the method was linear in the concentration range of 2-333 microg/ml of IgG with linear regression coefficients of 0.984, 0.998, and 0.990 for acidic, main and basic species, respectively. Limit of detection and limit of quantitation were determined to be 3 and 11 microg/ml. The R.S.D. for intra- and inter-day precision as well as reproducibility was determined to be 0.2% or less for all pI values and 1.4% or less for acidic and main peak area distribution; the R.S.D. for basic peak area distribution was 5.7% or less. Robustness testing was performed by deliberately deviating +/-50% of pharmalyte concentration away from the desired condition. This deviation revealed a pI shift of only 0.06 units and resulted in no significant impact on area percent distribution. Utilization of iCE280 Analyzer eliminated the mobilization step associated with traditional capillary isoelectric focusing analysis and increased analytical throughput at least 2-fold.

Characterization of plant growth-promoting rhizobacteria using capillary isoelectric focusing with whole column imaging detection

Capillary isoelectric focusing (cIEF) can be a useful tool for the characterization and identification of microbes. Based on the whole column imaging detection (WCID) technique and using plant growth-promoting rhizobacteria (PGPR) as test microbes, we present a two-level cIEF characterization method for the characterization and identification of bacteria. Intact bacteria were first characterized according to their apparent isoelectric points measured by cIEF-WCID and then lysed bacteria were further characterized by cIEF profiling of the intracellular proteins. Cellular clustering was found to be the main experimental barrier for the characterization of intact bacteria. The addition of sodium chloride (100mM) to the sample mixture was found to be an effective way to reduce clustering. Due to the high efficiency and high resolution of cIEF-WCID, characterization of bacteria according to their intracellular proteins can be implemented simply and quickly without optimization of the experimental conditions. To improve the detection sensitivity with laser induced fluorescence (LIF)-WCID, the possibility to label bacteria with a non-covalent fluorescent dye, NanoOrange, was explored.

Preparative-scale isoelectric trapping separations in methanol–water mixtures

The typically low aqueous solubilities of small, hydrophobic organic ampholytic molecules limit the production rates that can be achieved in their isoelectric trapping (IET) separations and call for the use of hydro-organic mixtures as solvents. The compatibility of methanol-water mixtures and poly(ethylene terephthalate) substrate-supported isoelectric polyacrylamide hydrogels, developed for binary IET separations in a Gradiflow BF200IET unit, was investigated. The isoelectric polyacrylamide-based hydrogels retained their functional and mechanical integrities when the methanol concentration in the hydro-organic solvent mixture was kept at or below 25% (v/v). The utility of the hydro-organic media was demonstrated in the purification of a hydrophobic ampholytic compound, technical grade 4-hydroxy-3-(morpholinomethyl) benzoic acid. Production rates as high as 7 mg/h were achieved using small, 15 cm2 active surface area isoelectric membranes.

Continuous Electrophoretic Purification of Individual Analytes from Multicomponent Mixtures

Individual analytes can be isolated from multicomponent mixtures and collected in the outlet vial by carrying out electrophoretic purification through a capillary column. Desired analytes are allowed to migrate continuously through the column under the electric field while undesired analytes are confined to the inlet vial by application of a hydrodynamic counter pressure. Using pressure ramping and buffer replenishment techniques, 18% of the total amount present in a bulk sample can be purified when the resolution to the adjacent peak is approximately 3. With a higher resolution, the yield could be further improved. Additionally, by periodically introducing fresh buffer into the sample, changes in pH and conductivity can be mediated, allowing higher purity (>or=99.5%) to be preserved in the collected fractions. With an additional reversed cycle of flow counterbalanced capillary electrophoresis, any individual component in a sample mixture can be purified providing it can be separated in an electrophoresis system.

Positively Charged Sol−Gel Coatings for On-Line Preconcentration of Amino Acids in Capillary Electrophoresis

A novel on-line method is presented for the extraction and preconcentration of amino acids using a sol-gel-coated column coupled to a conventional UV/visible detector. The presented approach does not require any additional modification of the commercially available standard CE instrument. Extraction, stacking, and focusing techniques were used in the preconcentration procedures. Sol-gel coatings were created by using N-octadecyldimethyl[3-(trimethoxysilyl)propyl]ammonium chloride (C18-TMS) in the coating sol solutions. Due to the presence of a positively charged quaternary ammonium moiety in C18-TMS, the resulting sol-gel coating carried a positive charge. For extraction, the pH of the samples was properly adjusted to impart a net negative charge to amino acids. A long plug of the sample was then passed through the sol-gel-coated capillary to facilitate extraction via electrostatic interaction between the positively charged sol-gel coating and the negatively charged amino acid molecules. Focusing of the extracted amino acids was accomplished through desorption of the extracted amino acid molecules carried out by local pH change. Two different methods are described. Both methods showed excellent extraction and preconcentration effects. Preconcentration results obtained on sol-gel-coated columns were compared with the CZE analysis performed on bare fused-silica columns with traditional sample injections. The described procedure provided a 150,000-fold enrichment effect for alanine. The two methods provided acceptable repeatability in terms of both peak height and migration time.

Preparative-scale isoelectric trapping enantiomer separations

The new Gradiflow BF200 IET unit, developed for isoelectric trapping protein separations has been modified and used to carry out preparative-scale enantiomer separations. Hydroxypropyl beta-cyclodextrin was used as the chiral resolving agent to induce an isoelectric point difference between the enantiomers. Three isoelectric membranes with isoelectric points below, in between and above the isoelectric points of the complexed enantiomers were used to trap the separated enantiomers in the anodic and cathodic separation compartments of the Gradiflow BF200 IET apparatus, respectively. The production rates were about 15 times higher than those previously obtained with another isoelectric trapping device and about 30% higher than those obtained in a continuous free-flow electrophoretic device operated in the isoelectric focusing mode. The remarkable separation speed observed in the modified Gradiflow BF200 IET unit is attributed to the favorable interplay of the short electrophoretic transfer distance, the high electric field strength and the large effective surface areas of the isoelectric membranes.

Effect of feed zone width on product purity in preparative-scale, continuous free-flow isoelectric focusing separation of enantiomers

The effects of the increased width of the sample feed stream upon the purity of the collected fractions were examined in the continuous free-flow isoelectric focusing separation of the enantiomers of dansyl-tryptophan. Compared to the reference separation obtained with a narrow feed stream introduced through the central sample feed port of the continuous free-flow isoelectric focusing separation unit, the final pH gradient, the position of the enantiomer band centroids and the values of the cumulative product recoveries and cumulative product purities remained essentially identical as the width of the feed band of the racemic sample dissolved in the carrier ampholyte was increased up to the full width of the separation chamber suggesting that the current, limiting practice of narrow, central feed bands can be safely abandoned and dilute feedstock solutions can be utilized in preparative-scale isoelectric focusing enantiomer separations.