Enantioseparation characteristics of biselector chiral stationary phases based on derivatives of cellulose and amylose

Abstract

Cellulose tris(4-methylphenylcarbamate) (CMPC) and cellulose tris(4-chlorophenylcarbamate) (CCPC) are well known for their powerful chiral recognition capability, and the chiral columns prepared from these two polymers have been commercialized. However, the chiral stationary phases (CSPs) can be only used in the mobile phases containing no more than 20% ethanol (referring to CMPC) or cannot be used in ethanol-containing mobile phases (referring to CCPC). In order to overcome the defect and to study the enantioseparation characteristics of biselector CSPs, CMPC, cellulose tris(phenylcarbamate) (CPC) and CCPC were, respectively, mixed with amylose tris(3,5-dimethylphenylcarbamte) (ADMPC) at a ratio of 1:1 (mol/mol) of glucose unit, and three new CSPs were prepared by coating the resulting blends on 3-aminopropyl silica gel. For the purpose of enantioseparation comparison, the corresponding single selector CSPs were also prepared with the individual derivatives of cellulose and amylose. The enantioseparation evaluation indicated that the biselector CSPs still bear excellent enantioseparation capability. The interaction between two polymers in each blend was investigated by using circular dichroism (CD) spectroscopy. Owing to the interaction, the durability of the biselector CSP derived from CMPC and ADMPC was significantly improved. The CSP could be analyzed with a mobile phase of 100% ethanol. And the biselector CSP derived from CCPC and ADMPC could safely work in a normal phase containing 30% ethanol. Therefore, the workable ranges of the mobile phases were broadened. The elution order on the biselector CSPs was generally dominated by the one on the corresponding single selector CSPs that provided a higher resolution. In addition, the suprastructure variation caused by the interaction between the individual polymers might also affect the enantioseparation of the biselector CSPs. The trends of the retention factors and the resolutions of partially racemic mixtures were discussed.