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

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• 作者：Abul K. Mallik ; Hongdeng Qiu ; Tomohiro Oishi ; Yutaka Kuwahara ; Makoto Takafuji ; Hirotaka Ihara
• 刊名：Analytical Chemistry
• 出版年：2015
• 出版时间：July 7, 2015
• 年：2015
• 卷：87
• 期：13
• 页码：6614-6621
• 全文大小：521K
• ISSN：1520-6882

文摘

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, ¹H NMR, diffuse reflectance infrared Fourier transform (DRIFT), solid-state ¹³C cross-polarization magic angle spinning (CP/MAS) NMR, suspended-state ¹H NMR, and differential scanning calorimetry (DSC). ²⁹Si 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 ¹³C CP/MAS NMR and suspended-state ¹H 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鈥揾ydrophobic substituents, the selectivity for the region and configurational differences in hydrophilic substituents, the evaluation of electrostatic interactions, and the evaluation of the acidic鈥揵asic 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, 尾-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 鈥渟mart phase鈥? 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.