Covalent cationic copolymer coatings allowing tunable electroosmotic flow for optimization of capillary electrophoretic separations

Highlights: • A surface for smooth tuning of electroosmotic flow in capillary electrophoresis. • Permanent covalent coatings based on cationic polyacrylamide-based co-polymers. • Anodic electroosmotic flow with mobility ranging from 0 to −40 × 10⁻⁹ m²V⁻¹s⁻¹. • Coating stability evaluated in the 2–10 pH interval. • Optimization of CE separations by balanced counter-current of electroosmotic flow. Electroosmotic flow (EOF) plays a pivotal role in optimization of capillary electrophoresis (CE) separations of (bio)molecules and (bio)particles. EOF velocity is directly related to analysis time, peak resolution and separation efficiency. Here, we report a concept of charged polymer coatings of the inner fused silica capillary wall, which allows anodic EOF with mobility ranging from 0 to ∼(30–40) × 10⁻⁹ m²V⁻¹s⁻¹. The capillary wall is modified by covalently bound cationic copolymer poly(acrylamide-co-(3-acrylamidopropyl)trimethylammonium chloride) (PAMAPTAC) containing variable ratio of the charged monomer in the 0–60 mol. % interval. The EOF mobility showed minor variability with composition of background electrolyte (BGE) and pH in the 2–10 interval. The coatings were evaluated by CE-UV and nanospray CE-MS in the counter-EOF arrangement for a series of basic drug molecules in acetic acid based acidic BGE. Tunable EOF velocity was demonstrated as a useful tool for optimization of peak resolution, separation efficiency and migration time of analytes. Electrostatic repulsion of positively charged capillary surface was shown as beneficial for suppression of analyte adsorption, notably for hydrophobic cationic analytes.