Preparation of a monolithic column with a mixed-mode stationary phase of reversed-phase/hydrophilic interaction for capillary liquid chromatography.

A monolithic capillary column with a mixed-mode stationary phase of reversed-phase/hydrophilic interaction chromatography was prepared for capillary liquid chromatography. The monolith was created by an in-situ copolymerization of a homemade monomer N,N-dimethyl-N-acryloxyundecyl-N-(3-sulfopropyl) ammonium betaine and a crosslinker pentaerythritol triacrylate in a binary porogen agent consisting of methanol and isopropanol. The functional monomer was designed to have a highly polar zwitterionic sulfobetaine terminal group and a hydrophobic long alkyl chain moiety. The composition of the polymerization solution was systematically optimized to permit the best column performance. The columns were evaluated by using acidic, basic, polar neutral analytes, as well as a set of alkylbenzenes and Triton X100. Very good separations were obtained on the column with the mixed-mode stationary phase. It was demonstrated that the mixed-mode stationary phase displayed typic dual retention mechanisms of reversed-phase/hydrophilic interaction liquid chromatography depending on the content of acetonitrile in the mobile phase. The method for column preparation is reproducible.