Fabrication of MOF-Functionalized Silica Monoliths and Their Unique Retention Behavior in HPLC

We report the development and characterization of stationary phases based on metal-organic frameworks (MOFs) composed of metal ions and organic ligands for use in high-performance liquid chromatography (HPLC). In particular, we focus on a subnanoporous MOF, [Zn₂(1,4-ndc)₂(ted)] _<i>n</i> (Zn-NDC; ndc = naphthalenedicarboxylate, ted = triethylenediamine), exploiting its intrinsic molecular adsorption and recognition capabilities to enhance chromatographic selectivity and efficiency. Zn-NDC was successfully immobilized onto silica monoliths through surface modification. The silica monolith substrate, functionalized with tertiary amine groups, enabled the stable and uniform attachment of Zn-NDC, leading to the successful preparation of a silica monolith modified with Zn-NDC (MOF-monolith). The MOF-monolith column exhibited distinct chromatographic behavior compared with a conventional packed-bed MOF column containing bulk Zn-NDC particles, suggesting that the continuous porous structure and surface chemistry of the silica monolith significantly influence analyte retention mechanisms. Furthermore, when C₁₈ fatty acid methyl esters were employed as analytes, the addition of ether compounds to a mobile phase dramatically altered their elution times and produced sharp, symmetric peak shapes. This phenomenon implies the existence of specific interactions between the ether functionalities and the Zn-NDC framework, highlighting the potential of MOF-silica hybrid monoliths as tunable and efficient stationary phases for advanced HPLC separations.