Critical parameters for highly efficient and reproducible polyelectrolyte multilayer coatings for protein separation by capillary electrophoresis

Surfactant-based coatings for protein separation by capillary electrophoresis - A review

BACKGROUND

Capillary electrophoresis (CE) is a highly efficient and versatile analytical method for the separation of biomacromolecules such as proteins and peptides. One major concern to reach high separation efficiency is the adsorption of analytes on the capillary wall and the heterogeneity of the capillary surface charge which generates hydrodynamic dispersion due to local electroosmotic (EOF) fluctuations.

RESULTS

Double chain surfactants have been described as potential interesting candidates for capillary coatings in CE. They are notably offering a very homogenous surface charge leading to very high separation efficiency with reported values up to 1 million plates per meter.

SIGNIFICANCE

This review provides an overview of double chain surfactant coatings used in CE with an emphasis on the coating protocol, the nature of the surfactant, the preparation of the coating solution (concentration, temperature, sonication or extrusion), the physicochemical parameters affecting their properties (pH, ionic strength, nature of the anion in the coating solution, coating additives, capillary internal diameter), and the coating stability/durability.

Charge variant analysis of monoclonal antibodies by CZE-MS using a successive multiple ionic-polymer layer coating based on diethylaminoethyl-dextran

The characterization of the impurities of pharmaceutical monoclonal antibodies (mAbs) is crucial for their function and safety. Capillary zone electrophoresis (CZE) is one of the most efficient tools to separate charge variants of mAbs; however, peak characterization remains difficult, since the hereby used background electrolytes (BGEs) are not compatible with electrospray ionization-mass spectrometry (ESI-MS). Here, a method that allows the separation of intact mAb charge variants is presented using CZE-ESI-MS, combining a cationic capillary coating and an acidic BGE. Therefore, a successive multiple ionic-polymer layer coating was developed based on diethylaminoethyl-dextran-poly(sodium styrene sulfonate). This coating leads to a relatively low reversed electroosmotic flow (EOF) with an absolute mobility slightly higher than that of antibodies, enabling the separation of variants with slightly different mobilities. The potential of the coating is demonstrated using USP mAb003, where it was possible to separate C-terminal lysine variants from the main form, as well as several acidic variants and monoglycosylated mAb forms. The presented CZE-MS method can be applied to separate charge variants of a range of other antibodies such as infliximab, NISTmAB (Reference Material from the National Institute of Standards and Technology), adalimumab, and trastuzumab, demonstrating the general applicability for the separation of proteoforms of mAbs.

Getting the Best out of Capillary Electrophoresis and Capillary Electrophoresis-Mass Spectrometry by Quantifying Sources of Peak Broadening for Proteins Using Polyelectrolyte Multilayer Coated Fused Silica Capillaries

Capillary electrophoresis (CE) has emerged as a relevant technique for protein and biopharmaceutical analysis, as it combines high separation efficiency, sensitivity, and versatility. The use of capillary coatings, including successive multiple ionic-polymer layers (SMILs), reduces interactions between analytes and the capillary, further improving the CE performance. Nevertheless, separations done on SMIL coatings rarely surpass 500 × 103 plates/m. To obtain the best out of the CE, it is interesting to have a detailed look at the sources of peak dispersion. Separations of a mix of model proteins were performed on (poly(diallyldimethylammonium chloride)/poly(styrenesulfonate))2.5-coated capillaries at different electrical field strengths, leading to plate height H against migration velocity u plots that enabled a quantitative analysis of each contribution. Using this model, capillary lengths and injected volumes were systematically varied. For the first time, the contribution of sample electrophoretic heterogeneity to the total peak dispersion was deciphered for model proteins and a monoclonal antibody. Dispersion due to electromigration was seen to have an impact on plate heights in the case of triangular peaks of small molecules but not for proteins under the present conditions. UV and mass spectrometry detections were compared on the same capillary, providing valuable information on the impact of the detection type on separation efficiency. Close to 1 million plates/m were reached in the best conditions.

Dual Contributions of Analyte Adsorption and Electroosmotic Inhomogeneity to Separation Efficiency in Capillary Electrophoresis of Proteins

Improving separation efficiency in capillary electrophoresis (CE) requires systematic study of the influence of the electric field (or solute linear velocity) on plate height for a better understanding of the critical parameters controlling peak broadening. Even for poly(diallyldimethylammonium chloride) (PDADMAC)/poly(sodium styrenesulfonate) (PSS) successive multiple ionic-polymer layer (SMIL) coatings, which lead to efficient and reproducible separations of proteins, plate height increases with migration velocity, limiting the use of high electric fields in CE. Solute adsorption onto the capillary wall was generally considered as the main source of peak dispersion, explaining this plate height increase. However, experiments done with Taylor dispersion analysis and CE in the same conditions indicate that other phenomena may come into play. Protein adsorption with slow kinetics and few adsorption sites was established as a source of peak broadening for specific proteins. Surface charge inhomogeneity was also identified as a contribution to plate height due to local electroosmotic fluctuations. A model was proposed and applied to partial PDADMAC/poly(ethylene oxide) capillary coatings as well as PDADMAC/PSS SMIL coatings. Atomic force microscopy with topography and recognition imaging enabled the determination of roughness and charge distribution of the PDADMAC/PSS SMIL surface.

Investigating cationic and zwitterionic successive multiple ionic-polymer layer coatings for protein separation by capillary electrophoresis

Successive multiple ionic-polymer layers (SMILs) have long since proved their worth in capillary electrophoresis as they ensure stable electroosmotic flow (EOF) and relatively high separation efficiency. Recently, we demonstrated that plotting the plate height (H) against the solute migration velocity (u) enabled a reliable quantitative evaluation of the coating performances in terms of separation efficiency. In this work, various physicochemical and chemical parameters of the SMIL coating were studied and optimized in order to decrease the slope of the ascending part of the H vs u curve, which is known to be controlled by the homogeneity in charge of the coating surface and by the possible residual solute adsorption onto the coating surface. SMILs based on poly(diallyldimethylammonium chloride) (PDADMAC) and poly(sodium styrene sulfonate) (PSS) were formed and the effect of each polyelectrolyte molar mass and of the number of polyelectrolyte layers (up to 21 layers) was studied. The use of polyethylene imine as an anchoring first layer was considered. More polyelectrolyte couples based on PDADMAC, polybrene, PSS, poly(vinyl sulfate), and poly(acrylic acid) were tested. Finally, zwitterionic polymers based on the poly(α-l-lysine) scaffold were synthesized and used as the last layer of SMILs, illustrating their ability to finetune the EOF, while maintaining good separation efficiency.

Size-based characterization of dendrigraft poly(L-lysine) by free solution capillary electrophoresis using polyelectrolyte multilayer coatings

Dendrigraft poly(L-lysine) (DGL) constitutes a promising dendritic-like drug vehicle with high biocompatibility and straightforward access via ring-opening polymerization of N-carboxyanhydride in water. The characterization of the different generations of DGL is however challenging due to their heterogeneity in molar mass and branching ratio. In this work, free solution capillary electrophoresis was used to perform selective separation of the three first generations of DGL, and optimized conditions were developed to maximize inter-generation resolution. To reduce solute adsorption on the capillary wall, successive multiple ionic polymer layer coatings terminated with a polycation were deposited onto the inner wall surface. PEGylated polycation was also used as the last layer for the control of the electroosmotic flow (EOF), depending on the PEGylation degree and the methyl-polyethylene glycol (mPEG) chain length. 1 kDa mPEG chains and low grafting densities were found to be the best experimental conditions for a fine tuning of the EOF leading to high peak resolution. Molar mass polydispersity and polydispersity in effective electrophoretic mobility were successfully determined for the three first generations of DGL.