Current trends in capillary isoelectric focusing of proteins

Deciphering nanoparticle protein coronas by capillary isoelectric focusing-mass spectrometry-based top-down proteomics

The nanoparticle (NP) protein corona significantly influences the outcome of nanomedicine. We present the first example of top-down proteomics (TDP) measurement of the protein corona using capillary isoelectric focusing-mass spectrometry, identifying seventy proteoforms of 16 cancer-related genes. This technique has the potential to revolutionize our understanding of the protein corona and advance nanomedicine.

Mobilization in two-step capillary isoelectric focusing: Concepts assessed by computer simulation

The mobilization step in a two-step capillary isoelectric focusing protocol is discussed by means of dynamic computer simulation data for systems without and with spacer compounds that establish their zones at the beginning and end of the focusing column. After focusing in an electroosmosis-free environment (first step), mobilization (second step) can be induced electrophoretically, by the application of a hydrodynamic flow, or by a combination of both means. Dynamic simulations provide insight into the complexity of the various modes of electrophoretic mobilization and dispersion associated with hydrodynamic mobilization. The data are discussed together with the relevant literature.

A Mini Review on Capillary Isoelectric Focusing-Mass Spectrometry for Top-Down Proteomics

Mass spectrometry (MS)-based top-down proteomics (TDP) requires high-resolution separation of proteoforms before electrospray ionization (ESI)-MS and tandem mass spectrometry (MS/MS). Capillary isoelectric focusing (cIEF)-ESI-MS and MS/MS could be an ideal method for TDP because cIEF can enable separation of proteoforms based on their isoelectric points (pIs) with ultra-high resolution. cIEF-ESI-MS has been well-recognized for protein characterization since 1990s. However, the widespread adoption of cIEF-MS for the characterization of proteoforms had been impeded by several technical challenges, including the lack of highly sensitive and robust ESI interface for coupling cIEF to MS, ESI suppression of analytes from ampholytes, and the requirement of manual operations. In this mini review, we summarize the technical improvements of cIEF-ESI-MS for characterizing proteoforms and highlight some recent applications to hydrophobic proteins, urinary albumin variants, charge variants of monoclonal antibodies, and large-scale TDP of complex proteomes.

Measuring protein isoelectric points by AFM-based force spectroscopy using trace amounts of sample

Protein charge at various pH and isoelectric point (pI) values is important in understanding protein function. However, often only trace amounts of unknown proteins are available and pI measurements cannot be obtained using conventional methods. Here, we show a method based on the atomic force microscope (AFM) to determine pI using minute quantities of proteins. The protein of interest is immobilized on AFM colloidal probes and the adhesion force of the protein is measured against a positively and a negatively charged substrate made by layer-by-layer deposition of polyelectrolytes. From the AFM force-distance curves, pI values with an estimated accuracy of ±0.25 were obtained for bovine serum albumin, myoglobin, fibrinogen and ribonuclease A over a range of 4.7-9.8. Using this method, we show that the pI of the 'footprint' of the temporary adhesive proteins secreted by the barnacle cyprid larvae of Amphibalanus amphitrite is in the range 9.6-9.7.

Isoelectric focusing in a silica nanofluidic channel: effects of electromigration and electroosmosis

Isoelectric focusing of proteins in a silica nanofluidic channel filled with citric acid and disodium phosphate buffers is investigated via numerical simulation. Ions in the channel migrate in response to (i) the electric field acting on their charge and (ii) the bulk electroosmotic flow (which is directed toward the cathode). Proteins are focused near the low pH (anode) end when the electromigration effect is more significant and closer to the high pH (cathode) end when the electroosmotic effect dominates. We simulate the focusing behavior of Dylight labeled streptavidin (Dyl-Strep) proteins in the channel, using a relationship between the protein's charge and pH measured in a previous experiment. Protein focusing results compare well to previous experimental measurements. The effect of some key parameters, such as applied voltage, isoelectric point (pI), bulk pH, and bulk conductivity, on the protein trapping behavior in a nanofluidic channel is examined.

cIEF for rapid pKa determination of small molecules: a proof of concept

A capillary isoelectric focusing (cIEF) method was developed for the determination of the ionization constants (pKa) of small molecules. Two approaches used to decrease the electroosmotic flow (EOF) were compared: (i) a hydroxypropylcellulose (HPC) coated capillary in aqueous medium and (ii) the addition of glycerol to act as a viscosifying agent. The cIEF method with the glycerol medium was selected, and the ionization constants of 22 basic and 21 acidic compounds, including 15 pharmaceutical drugs, were determined, resulting in pKa values from 3.5 to 7.4 and 6.4 to 9.3, respectively. cIEF offers an interesting alternative to other techniques for pKa determination with low sample consumption, high throughput and low cost.

Protein analysis by desorption electrospray ionization mass spectrometry and related methods

Desorption electrospray ionization mass spectrometry (DESI-MS) requires little to no sample preparation and has been successfully applied to the study of biologically significant macromolecules such as proteins. However, DESI-MS and other ambient methods that use spray desorption to process samples during ionization appear limited to smaller proteins with molecular masses of 25 kDa or less, and a decreasing instrumental response with increasing protein size has often been reported. It has been proposed that this limit results from the inability of some proteins to easily desorb from the surface during DESI sampling. The present study investigates the apparent mass dependence of the instrumental response observed during the DESI-MS analysis of proteins using spray desorption collection and reflective electrospray ionization. Proteins, as large as 66 kDa, are shown to be quantitatively removed from surfaces by using spray desorption collection. However, incomplete dissolution and the formation of protein-protein and protein-contaminant clusters appear to be responsible for the mass-dependent loss in sensitivity for protein analysis. Alternative ambient mass spectrometry approaches that address some of the problems encountered by spray desorption techniques for protein analysis are also discussed.

Method for estimation of protein isoelectric point

Adsorption of sample protein to Eu(3+) chelate-labeled nanoparticles is the basis of the developed noncompetitive and homogeneous method for the estimation of the protein isoelectric point (pI). The lanthanide ion of the nanoparticle surface-conjugated Eu(3+) chelate is dissociated at a low pH, therefore decreasing the luminescence signal. A nanoparticle-adsorbed sample protein prevents the dissociation of the chelate, leading to a high luminescence signal. The adsorption efficiency of the sample protein is reduced above the isoelectric point due to the decreased electrostatic attraction between the negatively charged protein and the negatively charged particle. Four proteins with isoelectric points ranging from ~5 to 9 were tested to show the performance of the method. These pI values measured with the developed method were close to the theoretical and experimental literature values. The method is sensitive and requires a low analyte concentration of submilligrams per liter, which is nearly 10000 times lower than the concentration required for the traditional isoelectric focusing. Moreover, the method is significantly faster and simpler than the existing methods, as a ready-to-go assay was prepared for the microtiter plate format. This mix-and-measure concept is a highly attractive alternative for routine laboratory work.

On-line sample pre-concentration in microfluidic devices: a review

On-line sample preconcentration is an essential tool in the development of microfluidic-based separation platforms. In order to become more competitive with traditional separation techniques, the community must continue to develop newer and more novel methods to improve detection limits, remove unwanted sample matrix components that disrupt separation performance, and enrich/purify analytes for other chip-based actions. Our goal in this review is to familiarize the reader with many of the options available for on-chip concentration enhancement with a focus on those manuscripts that, in our assessment, best describe the fundamental principles that govern those enhancements. Sections discussing both electrophoretic and nonelectrophoretic modes of preconcentration are included with a focus on device design and mechanisms of preconcentration. This review is not meant to be a comprehensive collection of every available example, but our hope is that by learning how on-line sample concentration techniques are being applied today, the reader will be inspired to apply these techniques to further enhance their own programs.

Online CIEF-ESI-MS in glycerol-water media with a view to hydrophobic protein applications

A new online coupling of CIEF with ESI-MS has been developed in glycerol-water media. This improved protocol provides: (i) the electric continuity during the whole analysis by a discontinuous filling of the capillary with 60:40 (cm/cm) catholyte/proteins-ampholyte mixture; (ii) the use of an anticonvective medium, i.e. 30:70 glycerol/water, v/v, compatible with MS detection and as an aid to hydrophobic protein solubilization and (iii) the use of unmodified bare fused-silica capillaries, as the glycerol/water medium strongly reduces EOF. Focusing was performed in positive polarity and cathodic mobilization was achieved by both voltage and pressure application. The setup was optimized with respect to analysis time, sensitivity and precision on pI determination. The optimized anolyte and catholyte were composed of 50 mM formic acid/1 mM glutamic acid (pH 2.35) and 100 mM NH(3)/1 mM lysine (pH 10.6), respectively. The effects of ampholyte concentration, focusing time and ESI parameters were presented for model proteins and discussed. This new integrated protocol should be an easy and effective additional tool in the field of proteome analysis, providing a means for the characterization of a large number of hydrophilic and hydrophobic proteins.

Fatty acyl structures of mycobacterium tuberculosis sulfoglycolipid govern T cell response

CD1b-restricted T lymphocytes recognize a large diversity of mycobacterial lipids, which differ in their hydrophilic heads and the structure of their acyl appendages. Both moieties participate in the antigenicity of lipid Ags, but the structural constraints governing binding to CD1b and generation of antigenic CD1b:lipid Ag complexes are still poorly understood. Here, we investigated the structural requirements conferring antigenicity to Mycobacterium tuberculosis sulfoglycolipid Ags using a combination of CD1b:lipid binding and T cell activation assays with both living dendritic cells and plate-bound recombinant soluble CD1b. Comparison of the antigenicity of a panel of synthetic analogs, sharing the same trehalose-sulfate polar head, but differing in the structure of their acyl tails, shows that the number of C-methyl substituents on the fatty acid, the configuration of the chiral centers, and the respective localization of the two different acyl chains on the sugar moiety govern TCR recognition and T lymphocyte activation. These studies have major implications for the design of sulfoglycolipid analogs with potential use as tuberculosis subunit vaccines.

CIEF with hydrodynamic and chemical mobilization for the separation of forms of α-1-acid glycoprotein

Alpha-1-acid glycoprotein (AGP) is a protein that exists in different forms, which is due to variations in the amino acid sequence and/or in the glycosidic part of the protein. These differences confer to these forms, among other characteristics, diverse pIs. Changes in these forms of AGP have been correlated to modifications of the pathophysiological conditions of the individuals. One of the analytical techniques employed for their study has been IEF performed in slab gels. CIEF method with hydrodynamic and chemical mobilization, involving an isotachophoretic process, is developed in this work to separate up to 12 bands of forms of standard AGP, which is proposed as a more reproducible, quantitative, less sample-consuming, and more automated one than conventional IEF. The challenge of this work has been the development of a CIEF method for the separation of bands of a very acidic protein (pI range: 1.8-3.8) in a capillary. Intraday RSD values < or = 1.7% have been achieved for the relative migration time of the AGP bands to that of an internal standard. For intraday area precision, RSD (%) in the range of 2.70-22.71% for AGP zones accounting for more than 10% of total area of AGP sample has been obtained. As a proof of the potential of the methodology proposed, an AGP sample purified from a pool of sera of patients suffering from ovary cancer is analyzed by CIEF.

Dual-opposite-injection CZE: Theoretical aspects and application to organic and pharmaceutical compounds

Several important figures of merit (migration time, efficiency, resolution, resolution per unit time, and electrophoretic selectivity) are quantitatively compared for the first time for conventional CZE and dual-opposite-injection CZE (DOI-CZE). Aspects of DOI-CZE relevant to the separation of organic and pharmaceutical ions (MW>120 Da) are also discussed. Two new approaches to resolve the codetection of anions and cations, hydrodynamic flow-modified DOI-CZE and polarity reversal in combination with asymmetric detector window positioning, are compared with the method of preliminary transport, a variable procedure within sequential sample introduction, using a six-component sample of organic and pharmaceutical compounds. The advantages of DOI-CZE for the simultaneous analysis of organic/pharmaceutical anions and cations are illustrated in a direct comparison of conventional CZE and DOI-CZE for the separation of a ten-component mixture of pharmaceutical ions (five ionized acids and five ionized bases).

Isoelectric focusing technology quantifies protein signaling in 25 cells

A previously undescribed isoelectric focusing technology allows cell signaling to be quantitatively assessed in <25 cells. High-resolution capillary isoelectric focusing allows isoforms and individual phosphorylation forms to be resolved, often to baseline, in a 400-nl capillary. Key to the method is photochemical capture of the resolved protein forms. Once immobilized, the proteins can be probed with specific antibodies flowed through the capillary. Antibodies bound to their targets are detected by chemiluminescence. Because chemiluminescent substrates are flowed through the capillary during detection, localized substrate depletion is overcome, giving excellent linearity of response across several orders of magnitude. By analyzing pan-specific antibody signals from individual resolved forms of a protein, each of these can be quantified, without the problems associated with using multiple antibodies with different binding avidities to detect individual protein forms.

Analysis of human blood serum using the off-line coupling of capillary isoelectric focusing to matrix-assisted laser desorption/ionization time of flight mass spectrometry

Off-line coupling of capillary IEF (CIEF) with matrix-assisted laser desorption/ionization mass spectrometry was utilized for the analysis of human blood serum. Serum proteins were initially separated by CIEF, and fractions of the isoelectric separation were eluted sequentially to a MALDI-TOF MS sample target. During pressure elution of the CIEF sample, voltage was maintained across the capillary system utilizing a sheath flow arrangement to minimize band broadening induced by the laminar flow field. Both pI and mass information were obtained from the complex biological sample, similar to traditional 2-DE techniques, and the platform was faster (hours versus days), more automatable, and simpler than 2-DE. The volume of raw sample present in the actual analysis was approximately 100 nL, making this technique well suited for very rare specimens. Additionally, the speed and simplicity of the technology make it an attractive technique for performing initial comparative analyses of complex samples.

Caillary electrophoresis for the analysis of meat authenticity

In this overview, different meat authenticity issues are presented, as well as a wide variety of methods available for meat authentication. Unlike chromatographic, traditional gel electrophoretic, or immunological methods, which have been routinely used in analytical laboratories, the application of capillary electrophoresis (CE) is relatively new in solving meat authentication issues. Several unique CE applications based on meat protein fingerprinting are discussed for the analysis of meat species in unheated meat products. For protein data interpretation, pattern recognition is used to account for the natural variability present within the same meat species. While gel DNA-based methods are widely used for determining meat species in heat processed products, few DNA-based methods utilizing CE have been reported. Moreover, the methods reported are qualitative or semiquantitative. Thus, the need for quantitative competitive PCR CE methods in the determination of meat species is addressed. For the determination of meat extenders, CE methods were either protein-based or based on specific markers. Polyphenols are used as specific markers for soy detection and hydroxyproline is used as a specific marker for collagen determination. Finally, the potential of electrophoretically mediated miroanalysis (EMMA) for the detection of meat that may have been previously frozen and retailed as "fresh" is highlighted.

Applications of capillary isoelectric focusing with liquid-core waveguide laser-induced fluorescence whole-column imaging detection

Capillary isoelectric focusing (CIEF) with liquid-core waveguide (LCW) laser-induced fluorescence (LIF) whole-column imaging detection (WCID) is a recently developed high-resolution, high-sensitivity, and high-speed analytical tool for protein analysis. Several potential applications of this system were demonstrated in this study. First, this system was employed to separate naturally fluorescent phycobiliproteins. Second, denaturing CIEF was suggested to study the conformational and chemical microheterogeneity and to characterize proteins with identical pI values. Third, a modified noncovalent fluorescent labeling procedure was presented, which allows the simple and effective labeling of proteins, antibodies, and viruses with reduced multiple labeling and preserved activity. Finally, extracellular proteins were suggested as signaling biomarkers for evaluation of cell viability. The separation of cyanobacteria and their extracellular phycoerythrins was demonstrated. The effectiveness of CIEF-LCW-LIF-WCID for the analysis of proteins, antibodies, viruses, and cells has been illustrated.

Determination of the isoelectric point of proteins by capillary isoelectric focusing

Different ways of determining isoelectric points (pI) of proteins in capillary isoelectric focusing are reviewed here. Due to the impossibility of direct pH measurements in the liquid phase, such assessments have to rely on the use of pI markers. Different types of pI markers have been described: dyes, fluorescently labelled peptides, sets of proteins of known pI values. It appears that, perhaps, the best system is a set of 16 synthetic peptides, trimers to hexamers, made to contain each a Trp residue for easy detection at 280 nm. By a careful blend of acidic (Asp, Glu), mildly basic, with pK around neutrality (His), and basic (Lys, Arg) amino acids, it is possible to obtain a series of pI markers with pI values quite evenly distributed along the pH scale, possessing good buffering capacity and conductivity around their pI values and thus focusing as sharp peaks. Another approach to pI determination is the monitoring of the current during mobilization: this allows, with the aid of known pI markers, to calibrate the system with a pI/current graph. Pitfalls and common errors in pI determinations are reviewed here and guidelines given for minimizing such errors in pI estimation.

Separation methods that are capable of revealing blood–brain barrier permeability

The objective of this review is to emphasize the application of separation science in evaluating the blood-brain barrier (BBB) permeability to drugs and bioactive agents. Several techniques have been utilized to quantitate the BBB permeability. These methods can be classified into two major categories: in vitro or in vivo. The in vivo methods used include brain homogenization, cerebrospinal fluid (CSF) sampling, voltametry, autoradiography, nuclear magnetic resonance (NMR) spectroscopy, positron emission tomography (PET), intracerebral microdialysis, and brain uptake index (BUI) determination. The in vitro methods include tissue culture and immobilized artificial membrane (IAM) technology. Separation methods have always played an important role as adjunct methods to the methods outlined above for the quantitation of BBB permeability and have been utilized the most with brain homogenization, in situ brain perfusion, CSF sampling, intracerebral microdialysis, in vitro tissue culture and IAM chromatography. However, the literature published to date indicates that the separation method has been used the most in conjunction with intracerebral microdialysis and CSF sampling methods. The major advantages of microdialysis sampling in BBB permeability studies is the possibility of online separation and quantitation as well as the need for only a small sample volume for such an analysis. Separation methods are preferred over non-separation methods in BBB permeability evaluation for two main reasons. First, when the selectivity of a determination method is insufficient, interfering substances must be separated from the analyte of interest prior to determination. Secondly, when large number of analytes is to be detected and quantitated by a single analytical procedure, the mixture must be separated to each individual component prior to determination. Chiral separation in particular can be essential to evaluate the stereo-selective permeation and distribution of agents into the brain. In conclusion, the usefulness of separation methods during BBB permeability evaluation is immense and more application of these methods is foreseen in the future.

Advantages and limitations of coupling isotachophoresis and comprehensive isotachophoresis-capillary electrophoresis to time-of-flight mass spectrometry

Capillary isotachophoresis (ITP) and comprehensive isotachophoresis-capillary electrophoresis (ITP-CE) were successfully coupled to electrospray ionization (ESI) orthogonal acceleration time-of-flight mass spectrometry (TOF-MS) using angiotensin peptides as model analytes. The utility of ITP-TOF-MS and ITP-CE-TOF-MS for the analysis of samples containing analyte amounts sufficient to form flat-top ITP zones (30 microM) as well as for samples with trace analyte amounts (0.3 microM) was studied. Separations were performed in 150 microm internal diameter (I.D.) capillaries for the ITP experiments, and in 200 microm I.D. (ITP) and 50 microm I.D. (CE) capillaries for ITP-CE experiments. The fused-silica columns were coated with poly(vinyl alcohol) to suppress electroosmotic flow that can disrupt ITP zone profiles. The sample loading capacity in both ITP and comprehensive ITP-CE was greatly enhanced (up to 10 microl) compared with typical nanoliter-sized injection volumes in CE. It was concluded that ITP-TOF-MS alone was adequate for the separation and detection of high concentration samples. The outcome was different at lower analyte concentrations where mixed zones or very sharp peaks formed. With formation of mixed zones, ion suppression and discrimination could occur, complicating quantitative determination of the analytes. This problem was effectively overcome by inserting a CE capillary between the ITP and TOF-MS. In such an arrangement, samples were preconcentrated in the high load WTP capillary and then injected into a CE capillary where they were separated into non-overlapping peaks prior to their detection by TOF-MS. The advantage of this comprehensive arrangement, which we have described previously, is that there is no need to discard portions of the sample in order to avoid overloading of the CE capillary. The whole sample is analyzed by multiple injections from ITP to CE. Thus, this method can be used for the analysis of complex samples with wide ranges of component concentrations.

One-step capillary isoelectric focusing for the separation of the recombinant human immunodeficiency virus envelope glycoprotein glycoforms

One-step capillary isoelectric focusing was investigated as a rapid method to resolve the glycoforms of the heterogeneous recombinant human immunodeficiency virus (HIV) envelope glycoprotein (rgp 160sMN/LAI). The separation was performed in a poly(vinyl alcohol) (PVA) coated capillary using a mixture of ampholyte of narrow and wide pH range. A combination of saccaharose and 3-(cyclohexylamino)-1-propanesulfonic acid was shown to be the most efficient additive to avoid protein precipitation which occurs at a pH close to its pI. Although the calibration curve [isoelectric point (pI) vs. migration times] showed a non-linear relationship, an adequate linearity could be yielded for short pI ranges permitting to exhibit the acidic character of the different glycoforms of the rgp 160s MN/LAI (pI from 4.00 to 4.95). Reproducibility evaluated by comparing the performance of a polyacrylamide and a PVA coated capillary showed that low RSD values were obtained for intra-day (0.5 to 1.9%) and inter-day (1.6 to 7.6%) measurements using the PVA capillary. Moreover, the long term stability of the PVA capillary was demonstrated by measuring the variation of migration times of the protein markers for a long period of use. Finally, this method was able to differentiate the glycoform pattern of two close glycoproteins such as the rgp 160 of two sub-populations of the virus HIV-1.

Enantioseparation of derivatized amino acids by capillary isoelectric focusing using cyclodextrin complexation

Enantioseparation of dansylated as well as 6-aminoquinolyl-N-hydroxysuccinimidylcarbamate (AQC)-derivatized amino acids by means of capillary isoelectric focusing using various cyclodextrin derivatives is demonstrated. Separation is based on the enantioselective shift of the isoelectric points upon complexation with the chiral selectors. The zwitterionic, diastereomeric analyte-cyclodextrin complexes exhibited differences in the pI values up to more than 0.25 pI units. Enantioresolution was achieved for a number of derivatized amino acids and various selectors added to the carrier ampholyte solution. The hydroxypropyl-beta-cyclodextrin proved to be the best selector for this purpose. Enantioseparation as dependent on the selector concentration was evaluated in a range between 5 and 30 mM. Separation could be attained down to selector concentrations corresponding to a degree of complexation as low as 30%. The peaks appear according to the degree of complexation between the positions adopted without and with full complexation. The kinetics of complex formation and dissociation was fast enough in most instances to produce single peaks, even with complexation degrees near 0.5 and significant pI shifts. Peak widths were slightly enlarged in these instances. The method offers excellent perspectives for preparative applications.

Capillary isoelectric focusing with whole column imaging detection for analysis of proteins and peptides

Whole column imaging detection has been developed for capillary isoelectric focusing (CIEF) of proteins and peptides. In this imaged C1EF technique, a solution of sample and ampholytes was introduced into a short (4-5 cm), internally coated capillary stabilized by a cartridge. After applying high DC voltage, the isoelectric focusing process takes place and the focused zones are monitored in a real-time mode using the imaging detectors developed. Three types of imaging detectors have been developed including refractive index gradient, laser-induced fluorescence (LIF), and absorption. Of these, absorption imaging detection is the most practical at the present time due to its quantitative ability and universal characteristics. Whole column imaging detection eliminates the mobilization step required for single point detection after the focusing process. Therefore, it provides a fast analysis speed (3-5 min for each sample), and avoids the disadvantages associated with the mobilization process, such as distortion of pH gradient and loss in resolution. In this paper, we review the methodology of imaged CIEF as well as progress in instrumental development, IEF performed on a microchip, and the application to protein and peptide analysis.

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.

Electrophoretic methods for process monitoring and the quality assessment of recombinant glycoproteins

In many ways electrophoretic techniques appear ideal for quality monitoring of proteins and are thus well suited for the analysis of recombinant glycoproteins. The requirements of high throughput, comparative analysis and resolution of many variants are met by several electrophoretic techniques. A wide variety of such techniques are available to biotechnologists in the rapidly developing area of recombinant glycoproteins. It is the aim of this review to specifically cover recent work which has been applied to the analysis of DNA-derived glycoproteins, both from a process control standpoint and final product validation. All major areas of electrophoresis including sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), isoelectric focusing and techniques utilizing capillary electrophoresis are covered, with emphasis on analysis of glycoforms and oligosaccharide profiles of recombinant glycoproteins. As illustration, actual examples rather than standard glycoproteins are given to indicate the potential and limitations which may be encountered. It is anticipated that this review will prove a useful and practical guide to the latest developments by indicating the relevant merits of different methods.