Abstract:

Chromatography remains a cornerstone technique in analyzing chiral compounds. The development and selection of chiral stationary phases （CSPs） are central to achieving high-resolution enantiomeric separation. This study presents a novel regeneration and functionalization strategy for the preparation of high-performance superficially porous particle （SPP）-CSP， offering a promising alternative to conventional fully porous particle （FPP）-CSP. First， bonded phases on the surface of spent chromatographic column silica packing materials were removed using ultraviolet light （λ=254 nm） and hydrogen peroxide solution （3%， mass fraction）， thereby obtaining sub-3 μm regenerated SPP. The regenerated SPP were then amino-functionalized. Subsequently， under mild reaction conditions， carbonyldiimidazole-activated （2-hydroxyethyl）-β-cyclodextrin （HE-β-CD） was bonded onto the surface of the amino-functionalized SPP to prepare the SPP-CSP. For comparative evaluation， a CSP based on 3 μm commercial FPPs was prepared. Additionally， a commercial （2-hydroxypropyl）-β-cyclodextrin （Hp-β-CD） chiral column with identical particle size and structure was selected as a reference. This commercial column was used to investigate the selectivity differences among different cyclodextrin derivatives. The enantioseparation and overall chromatographic performance of the CSPs were systematically evaluated under both supercritical fluid chromatography （SFC） and reversed-phase liquid chromatography （RPLC） modes. The evaluation was performed using ten chiral molecular probes： zopiclone， equol， 2-phenylpropionic acid， dobutamine， flutriafol， miconazole， folic acid， catechin， valacyclovir， and chlorphenamine. Results revealed that， under identical chromatographic conditions， the SPP-CSP consistently outperformed the FPP-CSP in terms of enantiomeric resolution， peak sharpness， theoretical plate number， and retention time efficiency. More importantly， the FPP-CSP exhibited a significant loss in resolution when chromatographic conditions were altered to yield equivalent analysis times. In contrast， the SPP-CSP showed only minor adverse effects on resolution when the flow rate was increased to shorten analysis time， highlighting its inherent suitability for ultrafast separations. Moreover， SFC and RPLC modes displayed complementary chiral recognition ranges. Within the overlapping separation scope of both modes， SFC mode achieved higher enantiomeric resolution and superior chromatographic performance. Notably， under RPLC mode， catechin showed high enantiomeric resolution on both CSPs， underscoring system-dependent selectivity differences. Multiple factors—including mobile phase composition （particularly the additive type）， and the stereochemical structure of the analytes—were found to significantly influence enantioseparation outcomes. Under SFC mode， none of the analytes could be eluted when acetonitrile was used as the mobile phase modifier， whereas alcohols effectively enabled elution， with weaker hydrophobicity correlating to stronger elution strength. Among the alcohols tested， methanol offered distinct advantages over isopropanol by maintaining lower backpressure and superior chromatographic performance without compromising resolution. Under RPLC mode， although isopropanol as a mobile phase component provided higher enantiomeric resolution， it resulted in relatively poorer chromatographic performance and higher column pressure drop. Using acetonitrile offered limited flexibility in adjusting elution strength. In both chromatographic modes， the influence trends of mobile phase additives on enantioseparation performance and overall column performance were generally consistent. Mobile phases with acidic additives were more suitable for analyzing acidic analytes such as 2-phenylpropionic acid and folic acid. Mobile phases with ammonium formate were better suited for analyzing basic analytes like chlorphenamine and flutriafol， as well as analytes with pK_a values near 7， such as zopiclone. In contrast， NH₃ as an additive yielded unsatisfactory results. Compared with the commercial Hp-β-CD chiral column of the same particle size and structure， the SPP-CSP exhibited different selectivity， which varied with the chromatographic mode. Under RPLC mode， the SPP-CSP showed higher resolution for zopiclone， dobutamine， and folic acid. Under SFC mode， it demonstrated higher resolution for equol， folic acid， and valacyclovir. Despite these advances， the study has certain limitations. To enhance compatibility with mass spectrometric detection， normal-phase mode was not investigated. Additives commonly used in chiral compound analysis， such as triethylamine and ammonium trifluoroacetate， were also not employed. Polar organic solvent mode was not investigated either. Additionally， peak symmetry and theoretical plate numbers on the SPP-CSP were generally inferior to those observed on the commercial Hp-β-CD chiral column across both chromatographic modes.

Key words: superficially porous particles, fully porous particles, chiral stationary phase, supercritical fluid chromatography （SFC）, reversed-phase liquid chromatography （RPLC）