Layer‑by‑Layer Assemblies Based on a Cationic β‑Cyclodextrin Polymer: Chiral Stationary Phases for Open‑Tubular Electrochromatography

Non-covalent chiral stationary phases for open-tubular capillary electrochromatography (OT-CEC) were developed using polyelectrolyte multilayer (PEM) coatings. These chiral coatings were made by alternately flushing the separation capillary with cationic and anionic polymers using a polymer of trimethylammonium-β-CD (pCD+) as a chiral selector. The layer-by-layer construction was monitored by EOF measurements. To our knowledge, it is the first OT-CEC chiral stationary phase based on a layer-by-layer assembly including an ionic cyclodextrin polymer. The composition of PEM coating was optimized as regards chiral separation. Thus, the influence of the nature of the first adsorbed cationic polymer (pCD+, polyethyleneimine or poly(diallyldimethyl ammonium chloride)) and the influence of the anionic polymer (poly(sodium 4-styrenesulfonate), polycarboxymethyl-β-CD or chondroitin sulfate) were studied with regard to the apparent surface charge and the enantioselective properties of the coatings. Interactions between the studied enantiomers and the internal layers of the stationary phase were pointed out. We found that the optimal stationary phase was based on a pCD+/poly(sodium 4-styrenesulfonate)/pCD+ three-layer coating. This optimal coating was found to be stable as evidenced by the RSD of 2.2 % for the EOF values calculated from five independent analyses. It was effective for the chiral separation of both neutral and anionic solutes.