Influence of spacers and organic modifiers on chromatographic behaviors on chiral diamide stationary phase with N-(3,5-dimethylbenzoyl)-D-phenylglycine

A chiral diamide stationary phase (CSP) with different length of spacers has been synthesized by chemically bonding the N-(3,5-dimethylbenzoyl)-D-phenylglycine on the aminopropylsilica gel or silica gel bonded with different carbon chain length of spacers. These CSPs have successfully been used for the chiral resolutions of the benzoyl-DL-octylamine and benzoyl-DL-amino acid isopropyl esters in normal-phase liquid chromatography (NP-LC). The spacer length and the introduction of a secondary amine group in the CSPs have been investigated. It has been found that a long spacer of CSPs generally benefits on the enantioselectivity. The introduction of secondary amine group in the spacer leads to the decline of separation factors. Further, the effect of organic modifiers has been examined. Proper use of organic modifiers resulted in an interesting ʹmasking effectʹ on the residing silanol groups of the CSPs. The addition of suitable amount of organic modifiers improves the enantioselectivity, and enantioselectivity depends on the shape of organic modifiers in the mobile phases.