Solvent-coordination-triggered framework breathing enables rapid polychlorinated biphenyls elution from magnetic Fe3O4/MIL-88B(Fe) composites.

Elution is often a time-consuming step in solid-phase extraction because strongly retained analytes must be efficiently released from the sorbent before instrumental analysis. Here, we develop a magnetic Fe3O4/MIL-88B(Fe) composite that combines rapid magnetic separation with coordination-assisted elution for the preconcentration of polychlorinated biphenyls (PCBs) from water. In our design, superparamagnetic Fe3O4 nanoclusters in Fe3O4/MIL-88B(Fe) enable rapid recovery of the composites from aqueous suspensions, while the flexible MIL-88B(Fe) framework provided a solvent-responsive environment for PCB retention and release. After adsorption and vacuum drying, the PCB-loaded composites were treated with solvents of different electron-donating ability. Strong donor solvents, such as pyridine, provided substantially greater PCB release than weakly coordinating solvents. The elution behaviour was therefore more closely associated with solvent donor strength than with analyte solubility, consistent with coordination-assisted reopening of the MIL-88B(Fe) framework. Under optimized conditions, enrichment of trace PCBs from high volume tap water can be accomplished, affording recoveries of 70.9-90.5% and enrichment factors of 354-452. This study demonstrates that solvent coordination can facilitate analyte release from flexible MOF sorbents, providing a practical strategy for rapid magnetic sample preparation of trace hydrophobic organic pollutants.