Design of C₁₈ Organic Phases with Multiple Embedded Polar Groups for Ultraversatile Applications with Ultrahigh Selectivity

Abstract

For the first time, we synthesized multiple embedded polar groups (EPGs) containing linear C18 organic phases. The new materials were characterized by elemental analysis, IR spectroscopy, (1)H NMR, diffuse reflectance infrared Fourier transform (DRIFT), solid-state (13)C cross-polarization magic angle spinning (CP/MAS) NMR, suspended-state (1)H NMR, and differential scanning calorimetry (DSC). (29)Si CP/MAS NMR was carried out to investigate the degree of cross-linking of the silane and silane functionality of the modified silica. Solid-state (13)C CP/MAS NMR and suspended-state (1)H NMR spectroscopy indicated a higher alkyl chain order for the phase containing four EPGs than for the phase with three EPGs. To correlate the NMR results with temperature-dependent chromatographic studies, standard reference materials (SRM 869b and SRM 1647e), a column selectivity test mixture for liquid chromatography was employed. A single EPG containing the C18 phase was also prepared in a similar manner to be used as a reference column especially for the separation of basic and polar compounds in reversed-phase liquid chromatography (RPLC) and hydrophilic interaction liquid chromatography (HILIC), respectively. Detailed chromatographic characterization of the new phases was performed in terms of their surface coverage, hydrophobic selectivity, shape selectivity, hydrogen bonding capacity, and ion-exchange capacity at pH 2.7 and 7.6 for RPLC as well as their hydrophilicity, the selectivity for hydrophilic-hydrophobic substituents, the selectivity for the region and configurational differences in hydrophilic substituents, the evaluation of electrostatic interactions, and the evaluation of the acidic-basic nature for HILIC-mode separation. Furthermore, peak shapes for the basic analytes propranolol and amitriptyline were studied as a function of the number of EPGs on the C18 phases in the RPLC. The chromatographic performance of multiple EPGs containing C18 HILIC phases is illustrated by the separation of sulfa drugs, β-blockers, xanthines, nucleic acid bases, nucleosides, and water-soluble vitamins. Both of the phases showed the best performance for the separation of shape-constrained isomers, nonpolar, polar, and basic compounds in RPLC- and HILIC-mode separation of sulfa drugs, and other polar and basic analytes compared to the conventional alkyl phases with and without embedded polar groups and HILIC phases. Surprisingly, one phase would be able to serve the performance of three different types of phases with very high selectivity, and we named this phase the "smart phase". Versatile applications with a single column will reduce the column purchasing cost for the analyst as well as achieve high separation, which is challenging with the commercially available columns.

HPLC Separation Of Bioactive Components Of Anti-Inflammatory Syrup On Stationary Phases With Embedded Polar Groups

“…Це може бути амідна, карбаматна або етерна група. Таких полярних груп в одній іммобілізованій молекулі може бути декілька [16]. Як і у бімодальних фазах, полярний фрагмент знаходиться біля поверхні носія та блокує утворення водневих зав'язків між аналітами основної природи та силанольними групами поверхні, Рис.1.…”

Preparation and evaluation a mixed‐mode stationary phase with C18 and 2‐methylindole for HPLC

“…Recently, to advance the separation of polar (Han, Zhang, Lu, & Zhang, 2019), cationic (Cai et al, 2012) and anionic structures (Bäurer et al, 2019; Song, Zhao, Xia, Liu, & Bai, 2019), the silica in chromatography columns was modified with hydrophobic hydrocarbon chains bearing different properties. Mixed‐mode stationary phases were obtained by surface modification simultaneous C 18 hydrophobic chain and ion exchange chromatography, such as C18SAX stationary (C 18 and strong anion‐exchange; Wei et al, 2012), RPLC/HILIC (hydrophilic interaction liquid chromatography) C18‐DTT (dithiothreitol; Wang et al, 2016), C18‐diol (Wang, Ye, Xu, & Shi, 2015), C 18 and an aryl sulfonate group (Ren et al, 2018), C 18 ‐embedded polar groups (Mallik et al, 2015) and RPLC/CEC/AEC (anion exchange chromatography) (Liu & Pohl, 2012). To achieve modified columns, the influential step is bridging between silica and the organic function.…”

Fabrication of Carbon-Like, π-Conjugated Organic Layer on a Nano-Porous Silica Surface

“…For instance, significant selectivity enhancement is observed for structural isomers of polycyclic aromatic hydrocarbons when heteroatom-based non-ionic polar groups such as carbonyl units are integrated in polymer side chains that are in highly ordered states. Typical examples have been reported in long chain alkylated polyacrylate [ 11 , 12 , 13 ], alternating copolymer systems with phthalimides [ 14 ], polypeptide-based [ 15 , 16 , 17 , 18 ], and lipidic-ordered [ 19 , 20 , 21 ] organic phases. These successful results are because of the promotion of multiple carbonyl–π interactions [ 22 , 23 ] with guest molecules.…”

“…Other useful integrations and orientations of interaction sites can be obtained by π-electron-rich π-conjugated polymer systems. A π–π interaction is weaker than a carbonyl–π interaction [ 19 , 20 , 21 , 22 , 23 ], but π-electrons can be highly dense in a vast plane. Typical examples are graphene and its related materials.…”