Performance of functionalized monolithic silica capillary columns with different mesopore sizes using radical polymerization of octadecyl methacrylate

Takeshi Hara; Gino V Baron; Kosuke Hata; Yoshihiro Izumi; Takeshi Bamba; Gert Desmet

doi:10.1016/j.chroma.2021.462282

Performance of functionalized monolithic silica capillary columns with different mesopore sizes using radical polymerization of octadecyl methacrylate

J Chromatogr A. 2021 Aug 16:1651:462282. doi: 10.1016/j.chroma.2021.462282. Epub 2021 May 26.

Authors

Takeshi Hara¹, Gino V Baron², Kosuke Hata³, Yoshihiro Izumi³, Takeshi Bamba⁴, Gert Desmet⁵

Affiliations

¹ Division of Metabolomics, Medical Institute of Bioregulation, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan; GL Sciences Inc., 237-2 Sayamagahara, Iruma, Saitama 358-0032, Japan.
² Vrije Universiteit Brussel, Department of Chemical Engineering, Pleinlaan 2, Brussels B-1050, Belgium.
³ Division of Metabolomics, Medical Institute of Bioregulation, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan.
⁴ Division of Metabolomics, Medical Institute of Bioregulation, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan. Electronic address: bamba@bioreg.kyushu-u.ac.jp.
⁵ Vrije Universiteit Brussel, Department of Chemical Engineering, Pleinlaan 2, Brussels B-1050, Belgium. Electronic address: gedesmet@vub.be.

PMID: 34144397
DOI: 10.1016/j.chroma.2021.462282

Abstract

We report on the possibility to enhance the phase ratio and retention factor in silica monoliths. According to pioneering work done by Núñez et al. [1], this enhancement is pursued by applying a stationary phase layer via radical polymerization with octadecyl methacrylate (ODM) as an alternative to the customary octadecylsilylation (C18-derivatization). The difference in band broadening, retention factor and separation selectivity between both approaches was compared. Different hydrothermal treatment temperatures for the column preparation were applied to produce monolithic silica structures with three different mesopore sizes (resp. 10, 13, and 16 nm, as determined by argon physisorption) while maintaining similar domain size (sum of through-pore and skeleton size). It has been found that the columns with the poly(octadecyl methacrylate)-phase (ODM columns) provided a 60 to 80% higher retention factor in methanol-water mixture compared to the octadecylsilylated (ODS) columns produced by starting from similar silica backbone structures. In acetonitrile-water mixture, the enhancement is smaller (15 to 30% times higher), yet significant. By adjusting the fabrication conditions (for both the preparation of the monolithic backbones and the surface functionalization), the achieved retention factors (up k = 4.89 for pentylbenzene in 80:20% (v/v) methanol/water) are obviously higher than obtained in the pioneering study on ODM monoliths of Núñez et al. [1], and column clogging could be completely avoided. In addition, also separation efficiencies were significantly higher than shown in Ref. [1], with plate heights as low as 5.8 μm. These plate heights are however inferior to those observed on the ODS-modified sister columns. The difference can be explained by the slower intra-skeleton diffusion displayed by the ODM-modified columns, in turn caused by the larger obstruction to diffusion originating from the thicker stationary phase layer.

Keywords: Column efficiency; Mesopore size; Monolithic silica; Phase ratio; Radical polymerization; Retention.

MeSH terms

Chromatography, High Pressure Liquid / methods*
Polymethacrylic Acids*
Porosity
Silicon Dioxide*

Substances

Polymethacrylic Acids
poly(octadecyl methacrylate)
Silicon Dioxide