Novel Approach for the Separation of Shape-Constrained Isomers with Alternating Copolymer-Grafted Silica in Reversed-Phase Liquid Chromatography

Abstract

This paper describes a novel packing material for high selective reversed-phase high-performance liquid chromatography (RP-HPLC). The organic phase on silica is chemically designed in a way that the weak interaction sites are integrated with high orientation along the polymer main chain and high selectivity can be realized by multiple interactions with solutes. For the above purpose, we synthesized poly(octadecyl acrylate-alt-N-octadecylmaleimide)-grafted silica (Sil-poly(ODA-alt-OMI)) stationary phase. The alternating copolymerization was carried out from 3-marcaptopropyltrimethoxysilane (MPS)-modified silica via surface-initiated radical-chain transfer reaction. Elemental analysis, diffuse reflectance infrared Fourier transform (DRIFT),(1)H NMR, solid-state (13)C cross polarization magic angle spinning (CP/MAS) NMR, and suspended-state (1)H NMR were used to characterize the new organic phase. Aspects of shape selectivity was evaluated with Standard Reference Material (SRM 869b), Column Selectivity Test Mixture for Liquid Chromatography. Enhanced molecular shape selectivity was observed, that lead to the separation of SRM 1647e (16 polycyclic aromatic hydrocarbons, PAHs) in an isocratic elution. The effectiveness of this phase was also demonstrated by the separation of several beta-carotene and tocopherol isomers. The complete baseline separation of the tocopherol isomers was achieved using the Sil-poly(ODA-alt-OMI) phase. Chromatographic study revealed that Sil-poly(ODA-alt-OMI) has extremely high separation ability compared to monomeric and polymeric C(18) columns. Higher shape selectivity of the new RP material can be explained by a pi-pi and dipole-dipole interaction mechanism.

Selectivity enhancement for the separation of tocopherols and steroids by integration of highly ordered weak interaction sites along the polymer main chain

“…Improvement in approaches used to characterize and design chemically modified surfaces have resulted in increased understanding of stationary-phase morphology, which in turn has permitted development of novel stationary phases with properties tailored for specific applications. Many groups including us have developed various special adsorbents and used in HPLC separation [3][4][5][6][7][8][9][10][11]. However, still the demands of developing new organic phases are necessary for many complex isomer separations.…”

“…On the other hand, we have been developing polymer or gel forming compound-grafted silica stationary phases based on carbonyl-π interaction mechanism [3,9,10]. Recently, we found that N-substituted maleimide-based alternating copolymer-grafted silica phase showed very good molecular-shape selectivity as well as the enhancement of separation selectivity [10,22,23].…”

A Facile and Specific Approach to New Liquid Chromatography Adsorbents Obtained by Ionic Self‐Assembly

“…[10] The term "molecular shape selectivity" is commonly used to refer to a chromatographic quality exhibited by certain stationary phases for enhanced separations of geometric isomers, depending on their molecular structure. [11] One successful means to achieve high selectivity for isomers is the use of liquid-crystalline stationary phases. [12] In GC, liquid crystals can be coated directly onto a solid support or capillary wall.…”

Preparation of high‐selective HPLC packing materials based on alternating copolymer‐grafted silica

“…Alternating copolymerization mediated by electron donor-acceptor interactions remains a popular approach for obtaining special materials with different functionalities in a wide range of scientific fields, including nanotechnology [31] and drug delivery [32]. Very recently, we reported the first application of an alternating copolymer, namely poly(ODA-alt-N-octadecylmaleimide (OMI)), grafted on silica for use in HPLC [33]. Here, styrene (ST) (p-electron rich) and N-methylmaleimide (MMI)/OMI (different alkyl chain lengths) monomers were chosen to verify the effect of p-electrons and alkyl chain length on selectivity enhancement in comparison with that of ODA, i.e.…”