Abstract: Metal-organic frameworks (MOFs) have attracted substantial attention as prospective media for next-generation chromatographic stationary phases and sample pretreatment matrices. Their utility is primarily attributed to their exceptional specific surface area, highly ordered and tunable pore architectures, and versatile surface chemistry, which theoretically enable precise molecular sieving and specific recognition. Nevertheless, the practical implementation of pristine MOFs is frequently constrained by intrinsic physicochemical defects, particularly the profound conflict between thermodynamic affinity and kinetic mass transfer. From a kinetic perspective, the exclusive microporous nature of most MOFs imposes excessive mass transfer resistance, especially for bulky analytes, leading to peak broadening and low column efficiency as described by the resistance to mass transfer term in the Van Deemter equation. Such kinetic limitations are particularly detrimental when analyzing macromolecules or performing high-speed separations, thereby hindering the throughput required for modern analytical workflows. Furthermore, practical deployment is often plagued by inadequate mechanical stability under high-pressure conditions, irregular crystal morphologies that induce significant eddy diffusion, and poor chemical stability in acidic or basic eluents, which significantly limits their direct utility in the high-efficiency analysis of complex matrices. To overcome these obstacles, the fabrication of MOF-based composites has evolved into a pivotal strategy within separation science. By integrating functional components through precise structural engineering, this approach exploits the synergistic complementarity of distinct materials to mask defects while amplifying advantages. This review systematically classifies current construction strategies into three primary architectures including core-shell structures, host-guest encapsulation, and skeleton hybridization. In core-shell architectures, MOF crystals are epitaxially grown on or chemically bonded to rigid microspheres such as silica or magnetic particles. This configuration effectively decouples the mechanical stability provided by the core from the separation performance governed by the shell. This design not only enhances mechanical robustness to withstand high backpressures but also shortens the diffusion path length to significantly improve mass transfer kinetics. Host-guest encapsulation strategies leverage the confinement effect of MOF cavities to act as nanocontainers for enzymes, chiral selectors, or metal nanoparticles. This approach effectively prevents the leaching and aggregation of active guests, thereby preserving their catalytic or recognition activities in complex matrices. Skeleton hybridization strategies, such as the construction of MOF-on-MOF or MOF-COF heterostructures, focus on lattice matching to ensure continuous pore channels across interfaces. This creates complex microenvironments that enhance selectivity through distinct steric and electronic interactions at the interface. In terms of applications, this review critically assesses the performance of these composites across various chromatographic modes. In high-performance liquid chromatography (HPLC), composites featuring hierarchical pore structures are shown to significantly ameliorate peak shapes and separation factors for challenging isomers and chiral drugs. For capillary electrochromatography (CEC), the review highlights how composites allow for the precise regulation of electroosmotic flow (EOF) through surface charge modulation, facilitating the separation of complex biological samples. Regarding gas chromatography (GC), where thermal stability is paramount, composite strategies involving covalent bonding or protective shelling are demonstrated to bolster structural integrity and effectively suppress column bleeding under rigorous thermal gradients. This enhancement is vital for maintaining baseline stability and detector sensitivity during high-temperature programming. Additionally, the role of these composites in sample pretreatment is also discussed, emphasizing their high enrichment factors and anti-interference capabilities in extracting trace targets from complex biological or environmental matrices. Finally, the review envisions future directions for this field. While current research has validated the concept of MOF-based composites, persistent challenges remain regarding the precision synthesis of defect-free interfaces, the enhancement of batch-to-batch reproducibility for commercial-grade production, and the development of smart stimuli-responsive separation media. Moreover, interdisciplinary collaboration between crystal engineering and chromatographic theory is essential to tailor these materials for specific, real-world separation challenges. Addressing these issues will be instrumental in realizing the full potential of MOF-based composites as high-performance separation media.

Key words: metal-organic frameworks, composites, chromatographic stationary phase, separation mechanism, review