Hydroxyl-Functionalized Acicular Single-Crystalline Covalent Organic Frameworks as Liquid Chromatographic Stationary Phases for the High-Performance Separation of Isomers.

Single-crystalline covalent organic frameworks (SCOFs) represent an emerging class of stationary phases for high-performance liquid chromatography (HPLC), yet their functionality and morphological diversity remain limited. Herein, hydroxyl-functionalized acicular SCOFs (A-SCOFs) were facilely synthesized at room temperature with uniform acicular morphology and shortened synthesis cycle, which were directly employed as an HPLC stationary phase. Unlike the design concept of traditional spherical stationary phases, the A-SCOF-packed column demonstrated efficient separation of small molecules and achieved baseline resolution for a range of isomers, including nitrophenol isomers, dichlorophenol isomers, and halogenated aromatic isomers driven by shape-selective mechanisms. Especially, the separation of nitrophenol isomers resulted in remarkable column efficiencies of 41,500 to 45,000 plates/m, and the corresponding resolutions (Rs) for o-/m-nitrophenol and m-/p-nitrophenol were 1.93 and 3.25, respectively. Comparative studies revealed superior separation performance of the A-SCOF-packed column over the commercial C18 column, particularly for challenging isomers. Furthermore, practical applicability was validated through successful separation of quinoid compounds in textile wastewater and methoxypsoralen isomers in Angelica dahurica extract. This work not only demonstrates the great potential of nonspherical functionalized SCOFs as advanced stationary phases for challenging separations but also broadens their application scope in the field of analytical science.