Pressure-based approach for the analysis of protein adsorption in capillary electrophoresis

Protein adsorption to inner capillary walls creates a major obstacle in all applications of capillary electrophoresis involving protein samples. The problem is especially severe in kinetic capillary electrophoresis (KCE) techniques, which are used to study protein-ligand interactions at physiological conditions and, thus, cannot utilize extreme pH. A variety of coatings exist to reduce protein adsorption in CE, each expressing a unique surface chemistry that interacts with individual proteins differently. Here we introduce a simple pressure-based method for the qualitative assessment of protein adsorption that can facilitate the direct antiadhesive ranking of several coatings toward a protein of interest. In this approach, a short plug of the protein is injected into a capillary and propagated through with a pressure low enough to ensure adequate Taylor dispersion. The experiment is performed with a nonmodified commercial instrument in a pseudo-two-detector approach. The two detectors are mimicked by using two different distances from the capillary inlet to a single detector. If the peak area and shape do not change with changing distance, the protein does not adsorb appreciably, while a decreasing peak area with increasing distance infers inner surface adsorption. The magnitude change of the peak area between the two distances along with the overall peak shape is used to gauge the extent of protein adsorption. By using this method, we ranked antiadhesive properties of different wall chemistries for a series of proteins. The described method will be useful for optimizing protein analysis by CE and, in particular, for KCE experiments that investigate how proteins interact with their respective ligands.