Optimization of the synthesis of a hyper‐crosslinked stationary phases: A new generation of highly efficient, acid‐stable hyper‐crosslinked materials for HPLC

Abstract

A new family of hyper-crosslinked (HC) phases was recently developed for use under very aggressive conditions including those encountered in ultra-fast, high-temperature two-dimensional liquid chromatography (2-DLC). This type of stationary phase has improved acid stability compared with the most acid-stable, commercial RPLC phases. Kinetic studies are here reported that allow optimization of reaction time and crosslinking reagent concentrations used to prepare such HC phases. We have determined that the Friedel-Crafts chemistry used to prepare HC phases is nearly complete within about 15 min. Thus, reaction time for each step of the synthesis was greatly reduced from the multihour reactions used previously without sacrificing the stationary phases' acid stability and separation performance. Results from elemental analysis of the finished particles were combined with LC data to provide insights regarding the properties of these HC phases. This new generation of acid stable HC phases, with their attractive chromatographic properties, should be very useful in the separations of bases or biological analytes in acidic media, especially at elevated temperatures.

Study of photorespiration in marine microalgae through the determination of glycolic acid using hydrophilic interaction liquid chromatography

“…Hydrolysis of the bonded phase at these low pH has been overcome by the use of sterically protected bonded phases that have been commercialized by Agilent and have been used for the separation of highly polar compounds such as peptides and proteins with mobile phases containing 0.1% m/v trifluoroacetic acid [29]. Another more recent approach to produce silica-based stationary phases stable under low pH is based on orthogonal polymerization reaction to prepare a monolayer of hyper-crosslinked aromatic network confined to the surfaces [30], resulting in stationary phases stable to media of 5% m/v trifluoroacetic acid at a temperature of 1501C [31]. These approaches, however, have not been used for the separation of low molar mass organic acids, probably because the pH around 2.5 that can be used with conventional RPLC columns is low enough to inhibit the ionization of most of these acids (Table 1).…”

Retention mechanism of hypercrosslinked polystyrene silica hybrid phase in normal phase chromatography

“…HC polystyrene silica hybrid phases can provide orthogonal selectivity in ultra-fast, 2D-LC [16]. A wide array of HC polystyrene silica hybrid phases have been developed, including HC-COOH [19], HC-C 8 [19], and HCTol [22]. Recently, our group observed that the HC-Tol phase provided unique and useful group-type selectivity for nitrogen containing compounds under normal phase conditions [23].…”

“…Recently, our group observed that the HC-Tol phase provided unique and useful group-type selectivity for nitrogen containing compounds under normal phase conditions [23]. In the HC-Tol phase, the silanized silica is primarily cross-linked, secondarily crosslinked and finally derivatized with toluene [24]. Despite the good reproducibility, high efficiency and better acid stability than most of the commercialized acid stable phases, these silica-base HC phases are not widely used [16].…”

“…The Carr group developed these polymer-silica hybrid phases as acid and thermal stable phases for RPLC [15][16][17][18][19][20][21][22]. The highly crosslinked aromatic network prevents loss of stationary phase under extreme conditions.…”

“…Normal phase HPLC separations have been performed with fully polymeric hypercrosslinked polystyrene [5,8] and with silica particles possessing a thin layer of highly crosslinked aromatic network [15][16][17][18][19][20][21][22]. The Carr group developed these polymer-silica hybrid phases as acid and thermal stable phases for RPLC [15][16][17][18][19][20][21][22].…”