High-performance liquid chromatography separation of unsaturated organic compounds by a monolithic silica column embedded with silver nanoparticles.

Article first published online: 15 JUL 2015The optimization of a porous structure to ensure good separation performances is always a significant issue in high-performance liquid chromatography column design. Recently we reported the homogeneous embedment of Ag nanoparticles in periodic mesoporous silica monolith and the application of such Ag nanoparticles embedded silica monolith for the high-performance liquid chromatography separation of polyaromatic hydrocarbons. However, the separation performance remains to be improved and the retention mechanism as compared with the Ag ion high-performance liquid chromatography technique still needs to be clarified. In this research, Ag nanoparticles were introduced into a macro/mesoporous silica monolith with optimized pore parameters for high-performance liquid chromatography separations. Baseline separation of benzene, naphthalene, anthracene, and pyrene was achieved with the theoretical plate number for analyte naphthalene as 36, 000 m(-1). Its separation function was further extended to cis/trans isomers of aromatic compounds where cis/trans stilbenes were chosen as a benchmark. Good separation of cis/trans-stilbene with separation factor as 7 and theoretical plate number as 76, 000 m(-1) for cis-stilbene was obtained. The trans isomer, however, is retained more strongly, which contradicts the long- established retention rule of Ag ion chromatography. Such behavior of Ag nanoparticles embedded in a silica column can be attributed to the differences in the molecular geometric configuration of cis/trans stilbenes

Synthesis of hierarchically porous polymethylsilsesquioxane monoliths with controlled mesopores for HPLC separation

Sol–gel synthesis of macroporous polymethylsilsesquioxane (PMSQ) monoliths has been successful over the past decade, and applications to separation media have been investigated. However, the control of mesopores to tailor hierarchical porosity, which is promising for improvement of the separation efficiency, remains challenging. In particular, an independent control of meso- and macropores has not been achieved in PMSQ. Herein we present a method to synthesize PMSQ monoliths with well-defined macropores and controlled mesostructure (pore size ranging from 10 to 60 nm, total pore volume from 0.2 to 0.6 cm[3] g[−1]) via sol–gel accompanied by phase separation. Different Pluronic-type nonionic surfactants were used to control phase separation of the hydrophobic PMSQ network in aqueous media. Due to different packing density of the colloidal PMSQ constituents in the continuous skeletons in the micrometer-scale (termed as macropore skeletons) and their rearrangements through the hydrothermal post-treatment under basic conditions, mesopore characteristics have been successfully controlled independently of the preformed macropore structure. Separation columns for high-performance liquid chromatography (HPLC) have been fabricated using the PMSQ monoliths, and acceptable separation performances in both the reversed-phase and normal-phase modes have been demonstrated due to the presence of both hydrophilic silanol groups and hydrophobic methyl groups