Supraparticle powders as stationary phase materials for size-exclusion chromatography of nanoparticles

Designing tailored stationary phase materials is essential for extending chromatographic techniques from conventional molecular systems to the separation of (nano)particles. In this work, we investigate key aspects of the design of stationary phase materials using silica supraparticles. Supraparticles are defined spherical aggregates of sub-micron sized primary particles, which provide tunable pore sizes and thus form a variable model system to elucidate structure-property relations for the size-exclusion chromatography of colloidal nanoparticles. We fabricate supraparticles with tunable pore sizes (70-200 nm) and particle sizes (13-25 μm) and systematically enhance their mechanical stability through high-temperature sintering and binder reinforcement to ensure stability upon packing. Using gold nanoparticles (5-100 nm) as model analytes, we demonstrate pore size-dependent elution behavior, quantify accessible pore volume via the dimensionless distribution coefficient, and investigate the role of pore size and supraparticle size on column efficiency. We further demonstrate effective separation of nanoparticles from molecular impurities and agglomerates, as well as partial to near-complete separation of binary nanoparticle mixtures depending on their size differences. Moreover, we analyze the packing structure inside columns using X-ray micro-computed tomography, revealing packing defects as a key cause of moderate performance, underscoring the importance of optimized packing protocols. Using supraparticles as a versatile model system, our work offers practical insights into the design of tunable stationary phase materials for efficient nanoparticle separation via chromatography.