A chiral porous organic cage-modified restricted-access material achieves online analysis of serum samples containing enantiomers and positional isomers.

Restricted-access materials (RAMs) allow biological samples to directly enter the chromatographic column for analysis owing to the steric exclusion function ability for biomolecules and extraction function for small-molecule analytes, which promoting the development of rapid, efficient, and automated in vivo drug analysis. Few reports on chiral RAMs that have been used to analyze enantiomers and positional isomers in serum by direct injection in currently. In this study, a chiral porous organic cage material RCC3 was innovatively introduced into the inner surface of silica gel and modified the outer surface with polyethylene glycol to prepare a novel type of chiral RAM-RCC3, and reported the use of chiral RAM-RCC3 as a stationary phase for the separation of chiral compounds and positional isomers in blank serum using high-performance liquid chromatography. The novel RAM-RCC3 column exhibited good performance in the online analysis of nine enantiomers and five positional isomers in serum samples. The effects of analyte mass, temperature, and composition of the mobile phase on the separation of o-, m-, and p-nitrophenol in serum samples using the RAM-RCC3 column were also investigated. Even after 300 injections, the RAM-RCC3 column exhibited good reproducibility and stability. These results indicate the potential of the chiral RAM-RCC3 column as a stationary phase for direct injection analysis of both chiral separation and positional isomers in biological samples, which also rendering it suitable to be further developed as a new type of RAM for online analysis of various small molecules in biological samples.