Highly efficient protein separations in capillary electrophoresis using a supported bilayer/diblock copolymer coating

A surfactant/polymer wall coating consisting of the doubly chained cationic surfactant dimethyldioctadecylammonium bromide (DODAB) and polyoxyethylene (POE) 40 stearate is investigated. The coating is formed by simply rinsing a capillary with a solution containing DODAB and POE 40 stearate. The resultant coating is semi-permanent—demonstrating stable electroosmotic flow (EOF) even after a 60 min high pressure rinse with buffer. The EOF (−0.45 ± (0.23) × 10−4 cm2 V−1 s−1 at pH 7.4) is suppressed by more than a factor of ten compared to that observed for DODAB alone. Model protein mixtures were separated over a pH range of 3–10 with efficiencies of up to greater than 1 million plates/m for the basic proteins cytochrome c, lysozyme, ribonuclease A and α-lactalbumin, and the acidic proteins insulin chain A, trypsin inhibitor, and α-chymotrypsinogen A. Migration time reproducibility was 0.5–4.0% from run to run and 0.6–4.3% from day to day. Protein recoveries with this coating ranged from 84% to 97%.