Editorial on “Non-covalent capillary coatings for protein separations in capillary electrophoresis” by C.A. Lucy, A.M. MacDonald and M.D. Gulcev

Abstract

The use of coatings applied to the surface of the capillary is a common technique used in capillary electrophoresis. Such coatings can be applied either by covalent binding to the capillary wall, or by physical (non-covalent) binding. In the latter method, the normal approaches are either to flush the capillary with the coating material prior to filling it with the background electrolyte to be used in the separation (the “static coating” or “semi-permanent coating” approach), or to include the coating material as a component of the electrolyte itself (the “dynamic coating” approach). Typically, such capillary coatings are used to modify the separation by manipulating the electroosmotic flow or in some cases, to induce selectivity changes resulting from interaction of analytes with the coating. However, when proteins are to be separated, the capillary coating serves the specific purpose of inhibiting interactions between the proteins and the capillary wall. Without this inhibition, poor peak shapes are frequently obtained. The very high propensity with which proteins, especially basic proteins, adsorb to negatively charged silanol groups on the fused-silica capillary wall has long been a major impediment to the achievement of highly efficient and reproducible separations of these species by capillary electrophoresis. Overcoming this impediment has generated intense research activity, such that there is now a very extensive range of additives available. These include a wide array of surfactants (non-ionic, cationic and zwitterionic, having single or double aliphatic chains) and both dynamic and static polymer coatings employing a very diverse range of polymers. Users of capillary electrophoresis who wish to achieve the separation of a particular set of target proteins are therefore faced with an enormous set of possible coating materials, each with specific characteristics and performance. The choice of the correct coating can therefore be a difficult task. Professor Charles Lucy and his co-workers at the University of Alberta have made major contributions to the study of capillary coating materials and I was therefore delighted that he agreed to accept my invitation to prepare a review. The review which follows is an excellent overview of the field, it provides a comprehensive evaluation of the literature, a systematic classification of capillary coating materials (including their structures, properties and effects on separation characteristics), and also includes detailed descriptions of methods for the measurement of protein adsorption. This outstanding article will be of immense value to both experts and novices in the field of protein separations using capillary electrophoresis and I am sure that it will provide an outstanding resource of information on this topic.