Original Mesogenic Citronellol-Based Stationary Phase for Both Normal- and Reversed-Phase HPLC Modes: Properties and Applications
Résumé
In this work, the synthesis, characterization and chromatographic performance of a silica material chemically bonded with a liquid crystal based on terminal citronellol for HPLC separation were investigated. This bonded liquid crystal stationary phase denoted as LC-LCC8 resulted from the grafting of a mesogenic carboxylic acid, 3′-((3,7-dimethyloct-6-en-1-y1)oxy)-[1,1′-biphenyl]-4-carboxylic acid (LCC8), on 4-(1,1-dimethyldisiloxanyl)butan-1-amine. LCC8 was previously synthesized and characterized by proton NMR, and a nematic mesophase at 127 °C was confirmed by differential scanning calorimetry and microscopy. The resulting stationary phase LC-LCC8 was characterized by using diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy and elemental analysis. The granulometric distribution was evaluated by scanning electron microscopy (SEM) before and after grafting. An analytical column (150 mm × 2.1 mm × 5 µm) was packed with the stationary phase for the chromatographic study. The chromatographic behaviour of the stationary phase was first characterized using the Tanaka test, exhibiting an exceptionally high shape selectivity (αT/O = 3.9). In normal-phase mode, using a 92/8 cyclohexane/tetrahydrofuran (THF) (v/v) mixture as the mobile phase, the isomeric mixture (Z and E) of crotamiton was well separated. In reversed-phase mode, good selectivity was observed towards organic pollutants [polycyclic aromatic hydrocarbons (PAHs)] and pharmaceutical compounds (xanthines, steroids and antihistamines). The new bonded phase showed satisfactory results both in normal- and reversed-phases modes except in terms of peak shape. The temperature effect on the selectivity and resolution of LC-LCC8 was estimated by injecting different isomers at various temperatures ranging from 293 to 333 K, demonstrating an improved resolution of solutes at high temperatures, which was probably due to a change in orientation order of the grafted ligands.