Packing particles #
The vast majority of LC columns is packed with spherical particles with average diameters between 1.5 and 5 µm. Columns are fabricated using high-pressure slurry-packing techniques.
The particles tend to be highly porous, so as to yield a high surface area that offers sufficient retention and sample loadability. A narrow particle-size distribution is essential for achieving high chromatographic efficiencies (plate counts).
Surface homogeneity, chemical inertness and mechanical strengths are key properties of packing materials.
Core-shell particles #
Core-shell particles (a.k.a. superficially porous particles) have gained popularity in LC, because they offer higher efficiencies than fully porous particles. This is attributed to a narrower particle-size distribution.
Monoliths #
Contrary to packed-bed columns, a solid stationary phase is a single continuous element, which a high porosity and sufficiently large through pores to allow the mobile phase to be transported through the column. Monoliths can be created in-situ from low-molecular-weight chemicals in a sol-gel process.
Silica monolith may compete in efficiency with particle-packed columns, but high shrinkage during their formation restricts this advantage to narrow, capillary columns. Polymer monoliths are easier to prepare, but they show low efficiencies, especially for low-molecular-weight analytes in isocratic elution.
