Application of a modified linear solvation energy relationship (LSER) model to retention on a butylimidazolium-based column for high performance liquid chromatography

Abstract

Previously, a new HPLC stationary phase based on n-butylimidazolium bromide was investigated using a linear solvation energy relationship (LSER) to systematically evaluate the intermolecular interactions between 32 test solutes and the stationary phase. The results and further comparisons with conventional reversed phase systems revealed that retention properties are similar to phenyl phases in both methanol/water and acetonitrile/water mixtures. In this work, the LSER model is extended by including the degree of ionization molecular descriptor, D, which takes into account the pK a of ionizable analytes and the pH of the mobile phase. The D molecular descriptor has been further divided into D + and D − components that separately account for the ionization of basic and acidic solutes, respectively. This is the first study where the ionization terms for weakly acidic solutes and weakly basic solutes have been separated. LSER results obtained with the expanded solute set with and without the inclusion of the D + and D − solute descriptors were compared. The improved correlation and standard error obtained for the expanded test set in the presence and absence of the D + and D − descriptors (R 2 : 0.987 vs 0.846; se: 0.051 vs 0.163 for 60% MeOH) supports inclusion of these additional terms. Further, the coefficients obtained from the multiple linear regression for the expanded test set with the D + and D − descriptors was more consistent with the coefficients obtained when the test set included just neutral analytes. In addition, the expanded LSER model did a better job of predicting elution order for the ionizable analytes. This work provides further supporting evidence for the multimodal nature of the butylimidazolium stationary phase.

Normal Phase Chiral Separation of Hexahelicene Isomers Using a Chiral Surface Confined Ionic Liquid Stationary Phase

“…[29][30][31][32][33][34][35] Capillary electrophoresis and NMR studies have revealed that under aqueous conditions, imidazolium cations interact with halophenols through p-p stacking. [36] Linear solvation energy relation (LSER) studies using neutral aromatics have confirmed that SCIL phases exhibit multimodal retention [37] and behaved somewhat like phenyl phases under reversed-phase conditions. [38] While ionic liquid-based chiral selectors have been used as additives in capillary electrophoresis, [39] as stationary phases in gas [40,41] and liquid chromatography, [42] most of this previous work has relied on ion-pairing or hydrogen-bonding secondary interactions.…”

Versatile ligands for high-performance liquid chromatography: An overview of ionic liquid-functionalized stationary phases

“…10 pHÀpKa 1 þ 10 pHÀpKa and 10 pKaÀpH 1 þ 10 pKaÀpH respectively for acidic and basic solutes [78]. The new form of the LSER model was:…”

A novel surface-confined glucaminium-based ionic liquid stationary phase for hydrophilic interaction/anion-exchange mixed-mode chromatography

“…Apart from the conventional monocationic ILs, our group recently prepared several imidazolium dicationic ILs-based stationary phases exhibiting considerably high column efficiency under HILIC mode [11]. All the studies indicated that ILs-modified HPLC columns could retain a wide range of solutes through multimodal retention mechanism such as electrostatic, ionic, -and dipole interactions [17,18,24], and are enjoying increasing popularity as a promising class of HPLC stationary phases.…”