The use of multilayered capillaries for chiral separation by electrochromatography

Fused-silica capillaries were modified by the successively multiple ionic-polymer layer (SMIL) coating technique for a capillary electrochromatography (CEC) analysis of binaphthyl enantiomers. The SMIL coating capillaries consisting of three different polymers (A+–B−–C+ coating) were prepared by the alternative deposition of positively charged chiral or achiral polymers and negatively charged DNA. Previous studies have indicated that DNA–cationic polypeptide or synthetic polymer complexes immobilized onto the inner surface of the capillary worked as the chiral stationary phases for 1,1′-binaphthyl-2,2′-diyl hydrogen phosphate (BNP). In this study, to investigate the chiral recognition mechanism and optimize the CEC separation condition in the DNA–cationic polymer coating, effects of the chirality of the polymer unit, the strand of DNA, and the number of layer pairs on the separation were investigated. It should be noted that, since single stranded DNA (ssDNA) was more suitable to immobilize cationic polymers than double stranded DNA, the ssDNA–cationic polymer immobilized capillaries gave a stable electroosmotic flow and reproducible CEC analyses. As a result, a poly(ethyleneimine)–ssDNA–protamine (Prt) coating provided the best chiral separation of BNP. The high separation performance of the prepared capillary is discussed in terms of DNA/polycations interaction.