The HPLC Column and Stationary Phases

Compare GC with HPLC. The typical capillary GC column has an internal diameter around 

Each LC phase molecule is bonded to its solid support surface, but is less often cross-linked. 

The HPLC phase is so thin that it is not a fully randomized fluid, like a GC polymer coating. 

Usually it is impossible, due to steric hinderance or increasing crowding, to attach a molecule [like the —O—Si—(CH3)2CigH37 group] to every free silanol bonding site on the silica surface. 

These unreacted silanol sites lie closer to the mobile phase than in GC, and can easily act as active sites degrading the chromatography as described in Section 11.4. 

---