Connections between structure and performance of four cationic copolymers used as physically adsorbed coatings in capillary electrophoresis

In this work, the properties of four cationic copolymers synthesized in our laboratory are studied as physically adsorbed coatings for capillary electrophoresis (CE). Namely, the four copolymers investigated were poly(N-ethyl morpholine methacrylamide-co-N,N-dimethylacrylamide), poly(N-ethyl pyrrolidine methacrylate-co-N,N-dimethylacrylamide), poly(N-ethyl morpholine methacrylate-co-N,N-dimethylacrylamide) and poly(N-ethyl pyrrolidine methacrylamide-co-N,N-dimethylacrylamide). Capillaries were easily coated using these four different macromolecules by simply flushing into the tubing an aqueous solution containing the copolymer. The stability and reproducibility of each coating were tested for the same day, different days and different capillaries. It is demonstrated that the use of these coatings in CE can drastically reduce the analysis time, improve the resolution of the separations or enhance the analysis repeatability at very acidic pH values compared to bare silica columns. As an example, the analysis of an organic acids test mixture revealed that the analysis time was reduced more than 6-times whereas the separation efficiency was significantly increased to nearly 10-times attaining values up to 595,000 plates/m using the coated capillaries. Moreover, it was shown that all the copolymers used as coatings for CE allowed the separation of basic proteins by reducing their adsorption onto the capillary wall. Links between their molecular structure, physicochemical properties and their performance as coatings in CE are discussed.