Dual hydrophilic interaction‐RP retention mechanism on polar columns: Structural correlations and implementation for 2‐D separations on a single column

Abstract

We investigated the retention of phenolic acid and flavone antioxidants on five polar columns in buffered aqueous ACN mobile phases. All columns show mixed retention mechanism: RP in highly aqueous mobile phases and normal phase (hydrophilic interaction LC, HILIC) in mobile phases with high concentration of ACN. The Silica Hydride and the ZIC HILIC sulfobetaine zwitterionic columns show rather limited retention in the RP mode. The Luna HILIC column shows higher retention in both the HILIC and the RP modes in comparison to the PEG and DIOL columns. We characterized the selectivity of various HILIC systems using linear solvation energy relationship model with molecular structure descriptors characterizing selective molecular size, dipole-dipole and proton-donor/proton-acceptor interactions and we investigated the effects of the mobile phase composition on the linear solvation energy relationship characteristics of the separation phase systems to select suitable conditions for orthogonal HILIC separations in combination with RP systems. Dual retention mechanism offers possibilities for using complementary selectivity in the HILIC and the RP modes for sequential 2-D separations of natural antioxidants on a single Luna HILIC column. Column equilibration time of 15 min between alternating RP and HILIC gradient runs is sufficient for reproducible results.

Hydrophilic interaction liquid chromatography (HILIC)—a powerful separation technique

“…Plots of retention factor versus binary aqueous–organic mobile phase composition show a “U shape” [97, 98]. Minimum retention at the “U turn” composition of the mobile phase corresponds to the transition from the RP to the NP (HILIC in an aqueous–organic mobile phase) mechanism, and the retention at this point is usually very low [94, 99]. The U shape of k versus the volume fraction of an aqueous buffer φ (BUF) can be described by the following equation:The parameters a 1 , m 1 and m 2 of Eq.…”

Hydrophilic-subtraction model for the characterization and comparison of hydrophilic interaction liquid chromatography columns

“…Based on this method, Quiming et al developed a HILIC retention prediction model for ginsenosides on a polyamine-bonded stationary phase [25], and adrenoreceptor agonists and antagonists on unmodified silica [26], diol-bonded [27] and polyvinyl alcohol-bonded [28] stationary phases. Although Michel et al [29,30], Buszewski et al [31] and Jandera et al [32] used linear solvation energy relationships (LSERs) to characterize and compare different HILIC stationary phases, this kind of characterization and comparison only focused on a specific class of analytes, such as peptides [29,31], pesticides [30], phenolic acids and flavone compounds [32]. Recently, two additional molecular descriptors on electrostatic interactions were introduced by Chirita et al [33] to the LSER model for the investigation of the chromatographic behaviors of zwitterionic stationary phases.…”

Tetrazole-Functionalized Silica for Hydrophilic Interaction Chromatography of Polar Solutes

“…At present, three models, partitioning mechanism [1], adsorption mechanism [8], or combination of them is often used to elucidate the retention behavior in HILIC [8][9][10]. As it is well known, mixed retention mechanism leading to ''U-shape'' retention curve was often found for the solutes in the wide concentration range of water in mobile phase [9].…”

“…The most important characteristic of HILIC is that the retention times of analytes increase as their polarities increase while they decrease as the polarity of mobile phase increases [1]. As for the mechanisms of solutes, it is difficult to definitely clarify the retention process due to the complex interactions among the analytes, mobile phase, and stationary phase, but partition, and surface adsorption or combination of them is regarded as the prevailing mechanisms at present [1,[8][9][10]. Numerous experiments have proved that the separation materials show different retention characteristics and separation selectivity, depending on the chemical structure of the surface of the stationary phase.…”