Abstract:

Metal-organic frameworks (MOFs) are a class of porous crystalline materials composed of metal centers or clusters assembled with organic ligands. These materials possess excellent properties, such as large surface areas, high porosities, uniform pore sizes, and diverse structures. Thus, MOFs have been widely applied in various fields, including catalysis, adsorption, sensing, sample pretreatment, and chromatographic separation. The applications of MOFs as stationary phases for chromatographic separation and analysis have attracted considerable attention from the research community in recent years. Compared with traditional chromatographic stationary phases, such as mesoporous silica, nanoparticles, and porous layers, MOFs possess flexible and tunable pore sizes and structures, thereby enabling precise control over their intermolecular interactions. Furthermore, the wide range of functional ligands and topologies of MOFs could potentially facilitate the separation and analysis of complex samples. These unique advantages render MOFs highly suitable for constructing novel chromatographic stationary phases.
This article focuses primarily on the construction methods of MOFs as chromatographic stationary phases, and provides an overview of the latest research advancements in their applications in several chromatographic separation techniques such as high performance liquid chromatography (HPLC), gas chromatography (GC), and capillary electrochromatography (CEC). The existing methods for the preparation and construction of MOFs-based chromatographic stationary phases are classified and evaluated. The construction methods for MOFs as stationary phases for HPLC mainly include filling, precursor-doped polymerization, and post-modification. The construction methods for MOFs as stationary phases for GC predominantly include in situ growth, static coating, and dynamic coating. The stationary phases for CEC can be categorized into packed columns, monolithic columns, and open-tubular columns. Compared with monolithic and packed columns, open-tubular CEC (OT-CEC) offers numerous advantages, including a more flexible and convenient preparation method, enhanced compatibility with various separation media, and higher separation efficiency. Consequently, OT-CEC has emerged as an important method for investigating the preparation of stationary phases for CEC. Several methods such as physical adsorption, covalent attachment, and electrostatic interactions have been developed for the preparation and modification of MOFs-based CEC stationary phases, and extensive studies have been conducted to optimize the performance and applications of MOFs in OT-CEC. However, the existing methods for constructing MOFs-based chromatographic stationary phases present certain limitations. Therefore, the selection of the appropriate MOFs, optimization of their preparation methods, and examination of their performance in different separation modes have become the focus of intensive research.
This review also summarizes the different analytical targets (e. g., chiral small molecules, biomacromolecules, and nonchiral molecules) and corresponding separation effects achieved using various MOFs-based chromatographic stationary phases. Finally, future studies focusing on the development of MOFs as chromatographic separation media are discussed. Overall, this review provides a valuable reference for the rational construction and practical applications of advanced MOFs-based chromatographic stationary phases.

Key words: metal-organic frameworks (MOFs), chromatographic stationary phase, separation, review