Protein analysis by isoelectric focusing in a capillary array with an absorption imaging detector

Analysis of therapeutic monoclonal antibodies by imaged capillary isoelectric focusing (icIEF)

Imaged capillary isoelectric focusing (icIEF) is a preferred analytical method for determining isoelectric points (pIs) and charge heterogeneity profiles in biotherapeutic proteins. In this study, we optimized the icIEF method for an in-house IgG1κ monoclonal antibody (mAb-1) and assessed its reproducibility, robustness, and autosampler stability. The optimized method was used to evaluate batch-to-batch consistency in pIs for multiple lots of mAb-1 and determine the relative percentages of charge variants. We also tested the method's performance using multiple lots of another IgG1 mAb, commercially available as Herceptin (trastuzumab). Additionally, we designed and assessed native and denaturing platform icIEF methods for 11 other marketed mAbs, with pIs ranging from 6.0 (eculizumab) to 9.22 (tocilizumab).

Synthesis of UV-absorbing and fluorescent carrier ampholyte mixtures and their application for the determination of the operational pH values of buffering membranes used in isoelectric trapping separations

Success in isoelectric trapping separations critically depends on the knowledge of the accurate operational pH value of the buffering membranes used. Currently, due to a lack of easy, rapid, accurate methods that can be used for the post-synthesis determination of the operational pH value of a buffering membrane, only nominal pH values calculated from the amounts of the reagents used in the synthesis of the membranes and their acid-base dissociation constants are available. To rectify this problem, UV-absorbing and fluorescent carrier ampholyte mixtures were prepared by alkylating pentaethylenehexamine with a chromophore and a fluorophore, followed by Michael addition of acrylic acid and itaconic acid to the resulting oligoamine. Carrier ampholyte mixtures, with evenly distributed absorbance values across the 3<pI<10 range, were prepared by blending. The master blend served as the feed mixture in binary isoelectric trapping separations that used the buffering membrane to be characterized. The pI value of the most basic UV-absorbing or fluorescent carrier ampholyte collected in the anodic separation compartment, determined by full-column imaging capillary isoelectric focusing analysis, indicates the operational pH value of the separation membrane.

CE-based analysis of hemoglobin and its applications in clinical analysis

This review focuses on the developments and trends in CE including CIEF, CZE, MEKC, two-dimensional conjunction of CIEF-capillary gel electrophoresis, and MEKC-CZE on microfluidic devices coupled to different detection approaches, such as UV absorbance, LIF, MS, and chemiluminescence etc. for performing analysis of hemoglobin (Hb), also with an emphasis on its applications in clinical analysis. Analysis of human Hb is of important clinical sense for numerous hemoglobinopathies associated with the congenital defects and abnormal contents of Hb. The diversiform modes render CE a comprehensive primary clinical tool for Hb analysis, which is rapid, sensitive, high-resolution, and not labor-intensive.

Conductivity properties of carrier ampholyte pH gradients in isoelectric focusing

The conductivity properties of natural pH gradient created by carrier ampholytes were studied during the process of isoelectric focusing (IEF). IEF was performed in capillaries (10-30 mm long) or in microchips with the same channel length. A 10-30x reduction of the conductivity of the separation medium was observed during the establishment of pH gradient. Results obtained using different IEF voltages indicate that there is a nonlinear relationship between the conductivity of an established pH gradient and the applied electric field. Our theoretical analysis using a simplified model generated values that reasonably agree with the experimental data. In addition, we found that above a certain electric field ( approximately 300 V/cm), resolution does not increase with the applied voltage as predicated; we observed band-broadening and gel breakdown. The approach presented in this work can be used for optimization of the IEF separation and judicious selection of IEF conditions.

On-line coupling of high performance gel filtration chromatography with imaged capillary isoelectric focusing using a membrane interface

A high performance liquid chromatography system, a sample preparation device, and an imaged capillary IEF (CIEF) instrument are integrated and multiplexed on-line. The system is equivalent to two-dimensional polyacrylamide gel electrophoresis (2-D PAGE), by transferring the principle of 2-D separation to the capillary format. High performance liquid chromatography (HPLC) provides protein separation based on size using a gel filtration chromatography (GFC) column. Each eluted protein is sampled and directed to a novel microdialysis hollow fiber membrane device, where simultaneous desalting and carrier ampholyte mixing occurs. The sample is then driven to the separation column in an on-line fashion, where CIEF takes place. The fluidic technology used by our 2-D system leads to natural automation. The coupling of the two techniques is simple. This is attributed to high speed and efficiency of the sample preparation device that acts as an interface between the two systems, as well as the speed and simplicity of our whole column absorption imaged CIEF instrument. To demonstrate the feasibility of this approach, the separation of a mixture of two model proteins is studied. Sample preparation and CIEF were complete in just 4-5 min, for each of the eluted proteins. Total analysis time is about 24 min. Three-dimensional data representations are constructed. Challenges and methods to further improve our instrument are discussed, and the design of an improved horseshoe-shaped sample preparation sample loop membrane interface is presented and characterized.

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.

New set-up for capillary isoelectric focusing in uncoated capillaries

Substituted aminomethylphenol dyes, low-molecular-mass isoelectric point (pI) markers and hemoglobin samples from normal individuals and diabetic patients were used to test a new set-up of capillary isoelectric focusing (cIEF) in uncoated capillaries. In previous cIEF methods, a mixture of sample components and carrier ampholytes was applied in the capillary and analyzed. In the new set-up a fractionated injection protocol is used to apply a 'sandwich' ampholyte-sample-ampholyte plug in the capillary for analysis. This new set-up allows the separation of amphoteric compounds having pI values outside the pH region of the ampholytes applied in the capillary with high precision. The high resolution power of this technique was proven with the analysis of hemoglobin variants.