Room temperature fabrication of post-modified zeolitic imidazolate framework-90 as stationary phase for open-tubular capillary electrochromatography

Metal–organic frameworks (MOFs) are attractive as porous stationary phase for open-tubular capillary electrochromatography (OT-CEC) due to their fascinating structures and unusual properties. Here we report a directly covalent bonding approach to prepare uniform and dense MOF film on the inner wall of fused silica capillary at room temperature for OT-CEC. Zeolitic imidazolate framework-90 (ZIF-90) as a model MOF because it not only possesses large surface area and high stability but also provides the free aldehyde groups to bond to the inner surface of capillary via covalent bond. X-ray diffraction, scan electron microscopy, and UV–vis spectrophotometry were used to confirm the bonding of the ZIF-90 to the inner wall of the silica capillary. The ZIF-90 coating not only increased the phase ratio of open-tubular column, but also improved the interactions of tested analytes and the coating. Owing to the porous structure of ZIF-90 and hydrophobic interactions between the analytes and the organic ligands of ZIF-90, three groups of isomers, neutral and basic compounds and nonsteroidal anti-inflammatory drugs were well separated on the ZIF-90 bonded column. The precisions (relative standard deviation, RSD) of retention time, half peak width and peak area for three consecutive runs were 0.3–1.2%, 1.3–6.0% and 1.5–5.2%, respectively. The run-to-run, day-to-day, and column-to-column precisions (RSDs) for the electroosmotic flow of the ZIF-90 bonded column were 0.2%, 0.4%, and 1.9%, respectively. Moreover, the ZIF-90 bonded column could stand more than 230 runs without observable change in the separation efficiency.