Chitosan/polyacrylic acid/octadecene double-crosslinked network hydrogel functionalized porous silica microspheres for multimode liquid chromatographic separation

In this study, chitosan (CS) and polyacrylic acid (PAA) were used to construct a double-crosslinked network hydrogel, which was employed as the functional material for silica microspheres to prepare a CS/PAA hydrogel modified liquid chromatographic stationary phase. During preparation, octadecene (ODE) was introduced into the CS/PAA hydrogel to improve its hydrophobicity and separation ability. The electrostatic interaction between the amino group of CS and the carboxyl group of PAA effectively prevented the swelling of the CS/PAA hydrogel, which ensured the successful application of the obtained CS/PAA hydrogel@SiO2 in chromatographic analysis. Polar nucleosides/bases and B-vitamins were selectively separated using hydrophilic interaction liquid chromatography. Hydrophobic polycyclic aromatic hydrocarbons and alkylphenols were effectively separated through reversed-phase liquid chromatography. Moreover, the effective separation of aromatic positional isomers and chiral enantiomers was achieved. This study confirms the potential application of the CS/PAA hydrogel in chromatographic separation. What is noteworthy is that the method developed in this study also provides a feasible strategy to solve the swelling issue associated with the hydrogel-based liquid chromatographic stationary phase.

Study on the graft modification mechanism of macroporous silica gel surface based on silane coupling agent vinyl triethoxysilane

In this research, the graft modification mechanism of coupling agent vinyl triethoxysilane (KH-151) to macroporous silica gel was studied using a combination of multiple methods. SEM, FTIR, RAMAN, NMR and XPS were used to characterize the silica gel before and after grafting, determining the mechanism of the grafting reaction of the silane coupling agent. On this basis, the grafting rate of the coupling agent was accurately calculated by TGA weight loss. From the results of characterization, it can be seen that the coupling agent molecules have two connection types on the surface of silica gel, and the ratio of the two types is 43.51% and 56.49% respectively. The influences of hydration degree of the silica gel, coupling agent dosage and reaction temperature on the grafting rate were explored, and the optimal reaction conditions for the modification of macroporous silica gel were determined by the coupling agent through orthogonal experiments, that is, the hydration degree of silica gel of 10%, a coupling agent dosage of 12 mL, and a reaction temperature of 80 °C. Under optimal reaction conditions, the average grafting rate of the coupling agent vinyl triethoxysilane (KH-151) on macroporous silica gel is as high as 91.03%.

Study on the mechanism of the alkylation reaction on the surface of porous silica gel.

One-pot hydrothermal cross-linking preparation of poly(vinylpyrrolidone) immobilized silica stationary phase for hydrophilic interaction chromatography

Hydrothermally cross-linked polyvinylpyrrolidone (PVP) immobilized SiO₂ stationary phase (CPVP-Sil) was prepared via a green and facile one-pot method which was demonstrated for hydrophilic interaction liquid chromatography (HILIC) as well as reverse phase chromatography(RP). A water or organic solvent-insoluble permanent CPVP immobilizing on the silica particle surface can be formed simply by dipping silica particles into PVP solution and low temperature hydrothermal treatment. The cross-linked PVP network coating on SiO₂ endow it ring lactam functional groups which exhibited excellent separation ability of polar compounds by a typical HILIC retention mechanism at higher organic solvent contents (>55% ACN) and additionally polyvinyl groups for separation of alkylbenzenes in RP mode(<25% ACN). A high column efficiency of about 7 × 10⁴ plates per meter was obtained for the test catechol compound. Remarkably, the CPVP-Sil packing materials showed good stability in acid (at pH 3.5) or basic (at pH 9.5) conditions, with 5400-fold column volumes and 3500-fold column volumes respectively.

The preparation of a core–shell stationary phase by the in situ polymerization of a hydrophilic polymer on the surface of silica and its chromatographic performance

A method for the in situ polymerization of polymers on a silica surface was developed.

High efficiency and simple preparation of polyacrylamide coated silica stationary phase for hydrophilic interaction liquid chromatography

A polyacrylamide (PAM)-coated silica packing as a novel stationary phase for hydrophilic interaction liquid chromatography (HILIC) was produced firstly by thermal immobilization. The coated layer was formed by a simple and facile physical method that dipping silica spheres into a PAM solution and then stirring the mixture until the solution was evaporated absolutely, leaving a certain amount of PAM on the silica particles. Although there are no chemical bonds involved, the bleeding measurement and the background noise are acceptable. Polyacrylamide coated silica (PAM-Sil, mean diameter: 5 μm) demonstrated a good hydrophilic property and excellent separation efficiency, which was observed especially for several high polar analytes such as saccharides. It is much higher than bare silica or amino columns under the same conditions. Moreover the obtained stationary phase demonstrated good stability under our operation conditions. The specific preparing method offers an easy and economical way to manipulate the thickness of PAM coating and can be extended as a universal way to produce various polymer coated stationary phases with dipping-heating/stirring-evaporating procedure.

Nanogold hybrid silica gel and its 1-octadecanethiol self-assembled modified composite as a stationary phase for liquid chromatography

Au nanoparticle-hybridized silica (Au@sil) spheres were synthesized in one step as a liquid chromatographic stationary phase for the first time.

Poly(vinyl alcohol)–cationic cellulose copolymer encapsulated SiO2 stationary phase for hydrophilic interaction liquid chromatography

A poly(vinyl alcohol)–cationic cellulose copolymer encapsulated SiO₂ HILIC stationary phase is described, which exhibits excellent separation for various analytes.

Recent development in liquid chromatography stationary phases for separation of Traditional Chinese Medicine components

Traditional Chinese Medicine (TCM) is an ancient medical practice which has been used to prevent and cure diseases for thousands of years. TCMs are frequently multi-component systems with mainly unidentified constituents. The study of the chemical compositions of TCMs remains a hotspot of research. Different strategies have been developed to manage the significant complexity of TCMs, in an attempt to determine their constituents. Reversed-phase liquid chromatography (RPLC) is still the method of choice for the separation of TCMs, but has many problems related to limited selectivity. Recently, enormous efforts have been concentrated on the development of efficient liquid chromatography (LC) methods for TCMs, based on selective stationary phases. This can improve the resolution and peak capacity considerably. In addition, high-efficiency stationary phases have been applied in the analysis of TCMs since the invention of ultra high-performance liquid chromatography (UHPLC). This review describes the advances in LC methods in TCM research from 2010 to date, and focuses on novel stationary phases. Their potential in the separation of TCMs using relevant applications is also demonstrated.