Mixed Metal–Organic Framework Stationary Phases for Liquid Chromatography

Strategic
design of the stationary phase in liquid chromatography
(LC) is crucial for modern separation science. Herein, a design approach
using mixed metal–organic frameworks (MOFs) as tunable LC stationary
phases is proposed. Three MOFs with an isostructural pillared-layer
structure are employed, with pore sizes tuned by the systematic design
of the constituent ligands, using 1,4-benzenedicarboxylate (bdc),
1,4-naphthalenedicarboxylate (ndc), and 9,10-anthracenedicarboxylate
(adc). Packed columns filled with the MOFs and their mixed-particle/solid-solution
stationary phases are prepared and examined for the retention capability
of polyethylene glycol (PEG) in LC. While the MOF-packed columns filled
with binary mixtures of different MOF particles provide good control
of the retention with respect to the particle mixing ratio, the columns
filled with mixed-linker solid-solution MOFs show a significant multicomponent
effect on the retention behavior. Specifically, mixed-linker solid-solution
MOFs consisting of bdc/ndc binary ligands are found to show a strong
retention that surpasses even their parent MOFs, namely, pure bdc-
and ndc-MOF stationary phases. The retention behavior on the MOF-packed
columns is explained by the specific nanostructures of the solid-solution
MOFs, which affects the balance between substrate affinity and adsorption
kinetics into the MOF pores, dictating the total retention capability.
The results provide an extra dimension for stationary phase design
using MOFs as a promising recognition medium for LC.