Comparative evaluation of a one-pot strategy for the preparation of β-cyclodextrin-functionalized monoliths: Effect of the degree of amino substitution of β-cyclodextrin on the column performance

To further evaluate the feasibility and applicability of the one-pot strategy in monolithic column preparation, two novel β-cyclodextrin-functionalized organic polymeric monoliths were prepared using two β-cyclodextrin derivatives, i.e. mono(6-amino-6-deoxy)-β-cyclodextrin and heptakis(6-amino-6-deoxy)-β-cyclodextrin. In this improved method, mono(6-amino-6-deoxy)-β-cyclodextrin or heptakis(6-amino-6-deoxy)-β-cyclodextrin reacted with glycidyl methacrylate to generate the corresponding functional monomers and were subsequently copolymerized with ethylene dimethacrylate. The polymerization conditions for both monoliths were carefully optimized to obtain satisfactory column performance with respect to column efficiency, reproducibility, permeability, and stability. The obtained poly(glycidyl methacrylate-mono(6-amino-6-deoxy)-β-cyclodextrin- co -ethylene dimethacrylate) and poly(glycidyl methacrylate-heptakis(6-amino-6-deoxy)-β-cyclodextrin- co -ethylene dimethacrylate) monoliths exhibited a uniform structure, good permeability, and mechanical stability as indicated by scanning electron microscopy and micro-high-performance liquid chromatography experimental results. Because of the probable existence of multi-glycidyl methacrylate linking spacers on the poly(glycidyl methacrylate-heptakis(6-amino-6-deoxy)-β-cyclodextrin- co -ethylene dimethacrylate) monolith, the effect of the ratio of glycidyl methacrylate/heptakis(6-amino-6-deoxy)-β-cyclodextrin was especially studied, and satisfactory reproducibility could still be achieved by strictly controlling the composition of the polymerization mixture. To investigate the effect of the degree of amino substitution of β-cyclodextrin on column performance, a detailed comparison of the two monoliths was also carried out using series of analytes including small peptides and chiral acids. It was found that the β-cyclodextrin-functionalized monolith with mono-glycidyl methacrylate linking spacers demonstrated better chiral separation performance than that with multi-glycidyl methacrylate linking spacers.