Surface Modification of Silica with β-Alanine Derivatives for Unique Applications in Liquid Chromatography

Isoniazid-Modified Silica for Hydrophilic Interaction Chromatography and as an Adsorbent for Dye Removal in Wastewater Samples

The new isoniazid-derived material was synthesized with a surface-immobilizable functional group by a reaction between isoniazid and succinyl anhydride and grafted onto silica surfaces. The material was designed so that multiple functional groups could interact with the guest molecules. Initially, the silica surface was modified with 3-amipropyltrimethoxysilane. Succinyl isoniazid (SID) was synthesized and then immobilized to 3-aminopropylsilica by an amide coupling reaction to obtain Sil-SID. The ATR-FTIR and 1H NMR were used to characterize the SID before immobilization. After grafting, Sil-SID was confirmed by elemental analysis, ATR-FTIR, scanning electron microscopy, and thermogravimetric analysis (TGA). The same material was finally used as a stationary phase in hydrophilic interaction chromatography (HILIC) to separate nucleosides and nucleobases and as an adsorbent for wastewater treatment for the first time. Due to the presence of multiple functional groups and a heteroaromatic ring in the phase, it exhibited excellent separation for polar analytes in HILIC and, at the same time, exceptionally high adsorption capacity and removal efficiencies for an anionic dye in wastewater. The maximum adsorption capacity reached 714.3 mg/g at pH 3. Here, a single material (Sil-SID) was used as a stationary phase and an adsorbent with excellent performance in both cases. This work is a good example of material development and its multiple applications. It will also reduce the design and production costs of novel materials for various applications. A single material can serve two or more purposes.

An adhesive hydrogel functionalized silica sphere for polar analytes separation and analysis

In response to the challenges associated with the chromatographic separation of polar compounds, this study aims to devise a solution by introducing a novel stationary phase. Hydrogels, characterized by a three-dimensional network structure, have aroused wide attention owing to its functional designability, multiple interaction sites and good adhesion, etc. In this work, an adhesive hydrogel functionalized silica stationary phase (Sil@PVA/TA) was synthesized using physical coating technique. Due to the co-existence of hydroxyl and benzene ring in the hydrogel structure, the obtained composites materials exhibited excellent separation performance for various of compounds and excellent column efficiency up to 71385.6 plates/m for thymidine. Furthermore, the hydrogel functionalized silica demonstrated superior selectivity to bare silica, diol-column and NH2-column for the separation of various of polar molecules, including, nucleosides/bases, alkaloids, organic acids, antibiotics and amino acids. Notably, for alkaloids, which frequently encounter peak tailing issues, Sil@PVA/TA demonstrated superior peak shape compared with C18 column. In short, this study successfully synthesized a hydrogel functionalized silica stationary phase, offering a novel method for the separation and analysis of polar compounds.

Facile preparation of embedded polar group-containing pentafluorophenyl stationary phases for highly selective separations of diverse analytes

Pentafluorophenyl (PFP) stationary phase is one of the most important phases after the C18 phase in terms of its applications. Three embedded polar groups (EPG)-containing stationary phases were newly synthesized to act the EPGs as additional interaction sites. The silica surface was initially modified with (3-aminopropyl)trimethoxysilane (APS). The APS-modified silicas were coupled with 2,3,4,5,6-pentafluorobenzoic acid, 2,3,4,5,6-pentafluorophenylacetic acid, and 2,3,4,5,6-pentafluoro-anilino(oxo)acetic acid to obtain Sil-PFP-BA, Sil-PFP-AA, and Sil-PFP-AN phases, respectively. The new phases were characterized by elemental analysis, ATR-FTIR, scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). The phases were evaluated with the Tanaka and Neue tests in reversed-phase liquid chromatography (RPLC). In addition, they were characterized as hydrophilic phases by the Tanaka test protocol used in hydrophilic interaction chromatography (HILIC) separation mode. The Sil-PFP-AA phase showed the highest molecular shape selectivity in RPLC, while Sil-PFP-AN achieved the highest separability in HILIC compared to the commercial PFP reference column. The Sil-PFP-AA phase was successfully applied for the analysis of capsaicinoids from real samples of fresh chili peppers (Capsicum spp.) in RPLC and the Sil-PFP-AN phase for vitamin C (ascorbic acid) in HILIC.