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)] n (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.