Metal-organic framework mixed-matrix disks: versatile supports for automated solid-phase extraction prior to chromatographic separation

We present for the first time the application of metal-organic framework (MOF) mixed-matrix disks (MMD) for the automated flow-through solid-phase extraction (SPE) of environmental pollutants. Zirconium terephthalate UiO-66 and UiO-66-NH₂ MOFs with different size (90, 200 and 300 nm) have been incorporated into mechanically stable polyvinylidene difluoride (PVDF) disks. The performance of the MOF-MMDs for automated SPE of seven substituted phenols prior to HPLC analysis has been evaluated using the sequential injection analysis technique. MOF-MMDs enabled the simultaneous extraction of phenols with the concomitant size exclusion of molecules of larger size. The best extraction performance was obtained using a MOF-MMD containing 90 nm UiO-66-NH₂ crystals. Using the selected MOF-MMD, detection limits ranging from 0.1 to 0.2 μg L⁻¹ were obtained. Relative standard deviations ranged from 3.9 to 5.3% intra-day, and 4.7–5.7% inter-day. Membrane batch-to-batch reproducibility was from 5.2 to 6.4%. Three different groundwater samples were analyzed with the proposed method using MOF-MMDs, obtaining recoveries ranging from 90 to 98% for all tested analytes.