Silica Regeneration and Chiral Separation: Comparative Performance of (2-Hydroxyethyl)-β-Cyclodextrin-Grafted Superficially Porous Versus Fully Porous Particles in Reversed-Phase Liquid Chromatography and Supercritical Fluid Chromatography.

A wet oxidation method was developed to remove the bonded phase from silica-based packing materials in spent chromatographic columns, thereby regenerating sub-3 µm monodisperse superficially porous particles (SPPs). The (2-hydroxyethyl)-β-cyclodextrin was grafted onto the surface of the regenerated particles, creating a chiral stationary phase (CSP). For comparison, CSPs were also prepared based on commercially available fully porous particles (3 µm, FPPs) and commercially available SPPs (2.7 µm). The chiral separation performance of these CSPs was evaluated using nine racemic compounds in reversed-phase liquid chromatography (RPLC) and supercritical fluid chromatography (SFC). The results showed that the regeneration method effectively removed the bonded phase from the spent column packing materials while maintaining the structural integrity of the SPP. Under the same chromatographic conditions, the SPP-CSP achieved a comparable enantioselectivity relative to the FPP-CSP while demonstrating superior column efficiency. The SPP-CSP displayed higher enantioselectivity when chromatographic conditions were altered to yield equivalent analysis times. SFC and RPLC demonstrated complementary chiral recognition ranges. SFC achieved higher enantioselectivity and better chromatographic performance within their jointly effective separation ranges. Compared to commercially available (2-hydroxypropyl)-β-cyclodextrin column of identical structure and specifications, the (2-hydroxyethyl)-β-cyclodextrin SPP-CSP exhibits different enantioselectivity. CSPs prepared from regenerated SPPs exhibit no significant differences in chiral separation performance compared to commercially available SPPs of the same brand, structure, and specifications. The (2-hydroxyethyl)-β-cyclodextrin SPP-CSP, synthesized via a straightforward and uncomplicated method, demonstrates favorable stability and chiral resolution capabilities.