Metal–organic framework-based sorbents in analytical sample preparation

In the last decade, metal–organic frameworks (MOFs) have been regarded as one of the most important classes of materials in analytical applications due to their several unique properties including diverse structural topologies, modifiable pore size, high porosity, tunable surface area, diverse composition, and versatile functionality. It is well known that the current limitation of MOFs in the field of separation is their chemical and thermal stabilities. Therefore, enhancing the structural strength of MOFs via ligand modification (by hydrophobic ligands to prevent moisture attack) or cooperative combination of MOFs with some materials including metal/metal oxide nanoparticles, carbon-based nanomaterials, monoliths, quantum dots, polyoxometalates, silica, and polymers can lead to improve structural stability. For a better understanding of MOFs as sorbents in sample preparation, we summarize their design strategies and synthetic routes followed by a discussion of the introduction of defects in their structures as well as MOF-based composites. The application of MOFs for analytical extraction in various sample pretreatment techniques including solid-phase extraction, dispersive solid-phase extraction, magnetic solid-phase extraction, and solid-phase microextraction with different types of modes (fiber, in-tube, stir, stir-bar, and thin-film) are surveyed. Finally, we highlight challenges and future developments in the field to look for new solutions to analytical sample preparation problems.