Characterization of surface-confined ionic liquid stationary phases: impact of cation and anion identity on retention

Abstract

A series of surface-confined ionic liquid (SCIL) stationary phases for high-performance liquid chromatography were synthesized in-house. The synthesized phases were characterized by the linear solvation energy relationship (LSER) method to determine the effect of residual linking ligands and the role of the cation and the anion on retention. Statistical analysis was utilized to determine whether the system coefficients returned from multiple linear regression analysis of chromatographic retention data for a set of 28 neutral aromatic probe solutes were significantly different. Examination of the energetics of retention via kappa-kappa plots agrees with the results obtained from the LSER analysis. Residual linking ligands were determined to contribute reversed-phase-type retention character to the chromatographic system. Furthermore, retention on the SCIL phases was observed to be more profoundly affected by the identity of the anion than by that of the cation.

Ionic Liquid Applications in Peptide Chemistry: Synthesis, Purification and Analytical Characterization Processes

“…The commonly used ILs for this purpose are based on 1,3-dialkylimidazolium or N -alkylpyridinium cations with variably associated anions [ 91 , 93 ]. In 2010, the first example of SCIL applied to the separation of small peptides was reported by Chitta et al .…”

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

“…To gain more insights into the retention characteristics of SCIL SPs, Stalcup et al conducted a series of systematic studies on the RP retention mechanisms involved in the SCIL SP (Sil-C 8 ImC x -Br)-MP system via LSER model [74][75][76]. The chromatographic evaluations revealed that the e, v terms were always positive, while s negative, a and b fluctuated around zero.…”

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

“…Recently, HPLC stationary phases have been reported in which aromatic cations (e.g., alkyl imidazolium or pyridinium) cations, with a variety of associated anions (e.g., bromide, chloride, tetrafluoroborate) have been attached to silica sorbents, forming surface-confined ionic liquid (SCIL) stationary phases. [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.…”