Preparation and evaluation of tert-leucine derivative functionalized polymeric monoliths for micro-liquid chromatography

In this study, a novel functional monomer N -[1-( α -naphthyl)ethylaminocarbonyl]-D- tert -leucine-[2-(methacryloyloxy)ethyl] amide (NA-D- tert -Leu-MA) was synthesized, and then employed to prepare polymeric monoliths (240 mm × 100 μm id) functionalized with tert -leucine derivative through a single step thermo-initiated co-polymerization approach or a multi-step post-modification approach. The multi-step approach involves the post-modification of a thiol-containing monolith with NA-D- tert -Leu-MA via “thiol-ene”click reaction. The physicochemical properties of the resulting monoliths were characterized by scanning electron microscopy, energy-dispersive X-ray spectrometry and micro-liquid chromatography. Good column stability, permeability, efficiency and reproducibility were obtained for the optimized monoliths. The poly (NA-D- tert -Leu-MA- co -ethylene dimethacrylate) monolith prepared through the single step co-polymerization approach exhibited satisfactory achiral separation performance for various analytes, including phenols, aniline derivatives and intact proteins, while its enantioseparation ability is rather poor. In contrast to that, the monolith prepared through the multi-step post-modification approach showed much higher enantioselectivity for 7-nitro-2,1,3-benzoxadiazole (NBD)-derivatized amino acids. Three NBD-derivatized amino acids (theanine, proline and norleucine) could be baseline enantioseparated.